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Infection,  Immunity 

AND 

Serum  Therapy 


In  Relation  to  the  Infectious  Diseases 
of  Man 


By 
H.   T.    RiCKETTS,  M.D. 

LATE  ASSISTANT   PROFESSOR   OF    PATHOLOGY,  UNIVERSITY    OF    CHICAGO 


SECOND  EDITION 

Revised  and  Enlarged  by  the  Author  and  by  Geo.  F.  Dick,  M.D., 

Instructor  in  Pathology,  University  of  Chicago,  with 

Preface  by  Ludvig  Hektoen,  M.D 


CHICAGO 

American  Medical  Association  Press 
535  dearborn  avenue 

I9I3 


Copyright^  1913 
By    the    American    Medical    Association 


"PREFACE  TO  THE  SECOND  EDITION 


The  circumstances  that  led  to  the  first  publica- 
tion of  this  book  as  well  as  its  general  scope  and 
character  are  explained  fully  by  Dr.  Eicketts  in 
the  preface  to  the  first  edition.  The  book  met 
with  such  favorable  reception  that  the  edition  was 
exhausted  while  the  demand  continued  active. 
This  indicated  that  an  actual  want  had  been  met 
and  so  it  was  determined  to  publish  a  new  edition, 
revised  and  enlarged,  and  for  some  time  previous 
to  his  greatly  lamented  and  untimely  death  Dr. 
Ricketts  gave  freely  of  his  already  heavily  taxed 
energies  and  strength  to  the  work  of  revision. 

Surely  a  simple  word  or  two  in  tribute  to  the 
memory  and  achievements  of  Dr.  Eicketts  are  not 
out  of  place  at  this  point.  He  died  in  Mexico  City,. 
May  3,  1910,  at  the  age  of  39,  from  typhus  fever 
which  he  was  investigating  with  splendid  success 
when  he  was  taken  ill.  Thus  a  noble  and  inspiring 
career  of  large  service  to  humanity  and  of  rich 
promise  came  to  a  sudden  and  heroic  end.  During 
his  short  but  intensely  active  life  as  an  investi- 
gator in  the  field  of  infectious  diseases  Dr.  Eick- 
etts made  important  contributions  of  permanent 
value  to  medical  science :  he  greatly  advanced  our 
knowledge  of  blastomycosis;  he  solved  the  most 
important  problems  in  the  cause  and  transmission 
of  Eocky  Mountain  spotted  fever,  and  discovered 
that  this  disease  is  conveyed  by  a  tick  (Derma- 
centor  venustus  and  D.  modestus),  in  which  the 


iv  PREFACE  TO  THE  SECOND  EDITION. 

infection  is  hereditary,  thereby  enlarging  our 
understanding  of  the  part  insects  may  take  as 
carriers  of  disease;  he  demonstrated  that  the 
typhus  fever  of  the  Mexican  plateau,  tabardillo,  is 
carried  by  the  body  louse  (Pediculus  vestimenti). 
and  the  results  of  his  work  on  this  disease,  which 
he  had  only  just  begun,  will  be  of  fundamental 
significance  in  its  prevention  and  in  all  future 
investigation  as  to  its  cause  and  nature.  In  his 
death  "on  the  firing  line"  we  lost  an  investigator 
of  the  first  rank  whose  name  through  these  achieve- 
ments will  live  in  the  history  of  medical  science. 

When  the  papers  and  manuscripts  left  by  Dr. 
Eicketts  came  to  be  examined  it  was  found  that 
while  the  work  of  revision  and  enlargement  of  this 
book  was  very  far  from  complete  yet  he  had  car- 
ried it  so  far  that  it  seemed  unwise  not  to  attempt 
to  carry  it  through  to  completion.  Fortunately 
Dr.  George  F.  Dick  was  willing  to  take  up  the 
unfinished  task,  which  proved  to  be  a  much  larger 
one  than  was  anticipated  for  the  reason  that,  in 
addition  to  completing  the  revision  and  adding  a 
considerable  amount  of  new  material,  it  was  neces- 
sary also  to  secure  proper  coordination  and  balance 
between  the  different  parts  of  the  book. 

The  book  is  now  divided  into  an  introduction 
and  three  parts  instead  of  two  as  in  the  first  edi- 
tion. The  Introduction  and  Part  I  were  prepared 
by  Dr.  Eicketts  and  the  chapters  on  ^'^Sources  of 
Pathogenic  Micro-organisms"  and  on  "Special 
Features  of  Infection"  are  new.  Part  II  contains 
new  chapters  on  "Complement-Deviation,"  "Opso- 
nins," and  "Anaphylaxis,"  and  Part  III  chapters 
on  "Epidemic  Poliomyelitis,"  "Noma,"  and  "Kala- 
Azar,"  all  bv  Dr.  Dick.    The  old  chapters  in  Parts 


PREFACE  TO  THE  SECOND  EDITION.  v 

II  and  III  have  been  revised  by  Dr.  Dick  in  the 
light  of  recent  work  and  some  of  them  largely  or 
wholly  rewritten,  notably  those  on  "Syphilis"  and 
"Spotted  Fever."  As  a  result  the  size  of  the  book 
has  been  increased  nearly  200  pages.  It  has  been 
the  aim  throughout  to  follow  the  lines  laid  down 
by  Dr.  Eicketts  in  order  to  secure  an  adequate 
presentation,  suitable  for  physicians  in  general, 
of  the  large  subjects  of  infection  and  immunity 
as  illustrated  by  the  human  infectious  diseases  in 
the  light  of  modern  knowledge.  The  present 
intense  and  widely  spread  activity  of  investigation 
in  these  fields,  with  its  many  discoveries,  is  giving 
us  new  principles  and  methods  of  treatment,  cura- 
tive as  well  as  preventive,  and  of  diagnosis,  which 
require  a  thorough  mastery  by  the  physician  in 
order  that  they  may  be  used  to  the  best  advantage.^ 
It  is  my  belief  that  this  book  by  Dr.  Eicketts  as 
revised  and  enlarged  by  himself  and  Dr.  Dick  will 
be  of  real  service  to  the  physician  who  desires  a 
reliable  guide  to  a  helpful  understanding  of  the 
subjects  with  which  it  deals.  May  the  use  to 
which  it  is  put  show  that  the  labor  expended  on 
it  shall  not  have  been  in  vain. 

LuDviG  Hektoen. 
Chicago,  May  5,  1911. 


"PREFACE  TO  THE  FIRST  EDITION 


Immunity,  in  its  present  state  of  development, 
with  its  manifold  new  terms  and  special  methods 
of  experimentation,  is  a  subject  which  appears 
difficult  to  one  who  has  not  studied  the  newer 
literature  assiduously  and  grown  into  a  knowledge 
of  the  conditions  through  actual  work  in  the  lab- 
oratory. Much  of  the  literature  is  technical  in 
character  and  appears  in  journals  not  commonly 
found  in  the  hands  of  the  physician  and  student. 
Much  of  it  also  is  comparatively  recent,  and  its 
"essence'^  has  not  yet  appeared  in  books  which  are 
in  general  use.  The  literature  of  immunity,  more- 
over, grows  so  amazingly  that  the  analysis  even  of 
current  works  is  a  task  of  no  mean  proportions. 

At  the  same  time,  the  subject  is  one  of  great 
interest  and  importance,  and  there  exists  a  gen- 
eral wish,  frequently  expressed,  to  know  more 
about  the  recent  advances  and  the  conditions  which 
have  operated  against  the  success  of  serum  therapy 
on  a  broader  scale. 

The  editor  of  The  Journal  of  the  American 
Medical  Association,  appreciating  the  need  which 
seemed  to  exist,  requested  me  to  prepare  a  series 
of  articles  on  the  subject  of  '^Immunity,"  which 
should  present  the  general  principles  and  the 
important  theories  and  facts,  in  as  simple  a  man- 
ner as  possible.  These  articles  appeared  from  week 
to  week  during  1905  in  The  Journal  of  the  Amer- 
ican Medical  Association,  and  after  revision,  and 


viii  PREFACE  TO  THE  FIRST  EDITION. 

with  such  additions  as  would  contribute  to  tlie 
completeness  of  the  work,  they  are  now  collected, 
in  larger  type,  in  the  present  volume  and  under  a 
more  suitable  title. 

It  was  thought  best  to  treat  the  subject  broadly, 
to  begin  with  the  fundamental  principles  of  infec- 
tion and  resistance  and  to  introduce  the  reader  to 
the  more  complex  conceptions  of  the  present  time 
by  taking  him  briefly  over  the  main  historical  and 
developmental  steps. 

It  will  be  obvious  that  the  views  of  Ehrlich, 
concerning  the  production  of  antibodies,  the  nature 
of  the  reactions  into  which  the  latter  enter,  and  the 
methods  by  which  bacteria  produce  disease,  have 
been  utilized  extensively.  This  course  demands  no 
justification,  when  it  is  appreciated  that  by  no 
other  means  can  one  at  the  present  time  correlate 
a  multitude  of  well-established  facts  which  bear 
on  the  problems  of  immunity.  Whatever  may  be 
the  eventual  fate  of  the  side-chain  theory — and 
certain  phases  of  it  carry  the  aspect  of  finality — w^ 
should  appreciate  as  much  as  possible  the  extent  to 
which  it  has  shaped  modern  thought,  and  recognize 
that  it  has  won  an  imperishable  place  in  the  his- 
tory of  biologic  progress. 

It  should  also  be  understood  that  the  utilization 
of  the  side-chain  theory  in  no  sense  carries  with  it 
a  negation  of  the  importance  of  phagocytosis,  a 
fact  which  is  plainly  set  forth  on  pages  356-7. 
Without  doubt  the  role  of  the  phagocytes  in  recov- 
ery from  a  large  gropp  of  infections  is  on  a  better 
and  truer  basis  than  it  has  ever  been  before,  and 
for  this  condition  the  recent  work  on  opsonins  has 
been  most  significant. 


PREFACE   TO    THE  FIRST  EDITION.  ix 

In  relation  to  the  grouping  of  the  infectious 
diseases  adopted  in  Part  III,  attention  is  called 
to  the  explanatory  paragraph,  page  398. 

It  will  be  noted  that  a  bibliography  of  the  sub- 
ject of  immunity  has  not  been  added,  and  this 
needs  no  explanation  to  one  who  is  conscious  of 
the  massive  proportions  of  the  literature.  A  crit- 
ical analysis  of  the  entire  literature,  which  would 
not  have  been  in  harmony  with  the  endeavor  to 
present  the  topics  briefly  and  clearly,  and  which 
would  have  made  detailed  references  essential,  has 
not  been  attempted.  The  most  recent  literature 
on  the  various  subjects  is  accessible  through  the 
Index  Medicus,  or  the  index  prepared  semi- 
annually by  The  Journal  of  the  American  Medical 
Association. 

The  index  at  the  close  of  this  volume  serves  as 
a  glossary  of  terms,  the  explanations  of  which  may 
be  found  on  the  pages  referred  to. 

H.    T.    ElCKETTS. 

Chicago,  February,  1906. 


CONTENTS. 


Introduction:       Historical     and     Developmental 
Data    1-  12 


PART  ONE— PRINCIPLES  OF  INFECTION 

Chapter  I. 
Parasitism,  Infectiousness,  Contagiousness 13-  21 

Chapter  II. 
Infectious  Etiology 22-  32 

Chapter  III. 

Infection    Atria    and    the    Excretion    of    Micro- 
organisms       33-  40 

Chapter  IV. 

Sources  of  Pathogenic  Micro-Organisms : 

1.  Earth,    Etc 41-42 

2.  Food    Substances 42-  43 

3.  Animals     43-  45 

4.  Body  Surfaces  of  the  Individual 45-  46 

Chapter  V. 

Sources    of    Pathogenic    Micro-Organisms     (con- 
tinued) : 

5.  From   Man  to   Man 47-  63 

Chapter  VI. 

Sources    of    Pathogenic    Micro-Organisms     (con- 
cluded) : 

6.  Dissemination      and      Transmission      by 

Insects : 

A.  Dissemination    64-  67 

B.  Transmission   67-  87 


xii  CONTENTS. 

Chapter  VII. 

Special  Features  of  Infection: 

1.  Virulence,  Toxicity,  Etc 88-  94 

2.  Types  of  Infection 94-102 

3.  Nature  and  Mechanism  of  Infection 102- 127 


PART  TWO. 

Chapter  VIII. 
Types    of    Immunity 128-136 

Chapter  IX. 

Natural    Immunity 137 

1.  Protection  Afforded  by  the  Body  Surfaces.  .  137-143 

2.  Internal  Protective  Agencies: 

A.  Inflammation    143-149 

B.  Properties  of  the  Serum  and  Plasma.  .149-160 

Chapter  X. 
Acquired     Immunity 161-175 

Chapter  XI. 
Toxins  and  Antitoxins 176-190 

Chapter  XII. 

The  "Structure"   of   Toxins   and   Antitoxins    and 

the  Nature  of  the  Toxin- Anti-Toxin  Reaction.  .191-205 

Chapter  XIII. 
The  Phenomenon  of  Agglutination 206-218 

Chapter  XIV. 

The    Nature    of    the    Substances    Concerned     in 

Agglutination    219-233 

Chapter  XV. 
Precipitins    234-244 

Chapti.k  XVI. 

A.  General  Properties  of  Bactericidal  Serums.  .  .245-256 

B.  Hemolysins     256-278 


CONTENTS.  xiii 

Chapter  XVII. 
Complement   Deviation 279-291 

Chapter  XVIII. 
Cytotoxins    292-305 

Chapter  XIX. 
Phagocytosis    306-323 

Chapter  XX. 
Opsonins     324-338 

Chapter  XXI. 

The  Side-Chain  Theory  of  Ehrlich  and  Its  Rela- 
tion to  the  Theory  of  Phagocytosis 339-361 

Chapter  XXII. 
Principles   of   Serotherapy 362-380 

Chapter  XXIII. 
Anaphylaxis     381-397 


PART  THREE—SPECIAL. 

Chapter  XXIV. 
Group      I. — Diseases,     Natural     or     Experimental, 
Caused  by  Soluble  Toxixs  of  Bacterial,   Animal 
OR  Plant  Origin: 

A. — Bacterial  Diseases: 

Diphtheria    398-408 

Tetanus     408-419 

Botulism     419-422 

Bacillus   Pyocyaneus 422-425 

Other  Soluble  Bacterial  Toxins 425 

B. — Intoxication  hy  Soluble  Plant  Toxins: 

Hay  Fever 425-427 

Other    Plant    Toxins 427-428 

C. — Intoxication   hy  Soluble  Animal  Toxins: 

Poisoning  by  Snake  Bites 428-431 

Other    Zootoxins 431-432 


xiv  CONTENTS. 

Chapter  XXV. 
Group  II. 

A. — The  Serum  in  Acquired  Immunity  is  Increased  in 
Bactericidal  and  Opsonic  Power: 

Typhoid    Fever 433-449 

Paratyphoid    Fever 449-453 

Acute  Epidemic  Dysentery 453-459 

Meat  Poisoning  by  Bacillus  Enteritidis 459-463 

Bacillus    Coli 463-469 

Cholera  469-480 

Plague    481-492 

B. — Diseases  in  Which  Acquired  Immunity  is  Not  Due 
to  Increased  Bactericidal  Power  of  the  Serum,  or 
Knowledge  on  this  Point  is  Deficient: 

Anthrax    492-498 

Malta    Fever 498-500 

Chapter  XXVI. 

Grol'p    III. — Acute    Infections    in    Which    Lasting 
Immunity    is    Not    Established. 

Pneumococcus    Infections — Pneumonia 501-515 

Streptococci     515-537 

Staphylococci    537-550 

Micrococcus  Catarrhalis 550-551 

Gonorrhea   and  Other  Infections   with  the  Gono- 

coccus    551-556 

Epidemic    Cerebrospinal    Meningitis 556-563 

Influenza     563-569 

Soft  Chancre 569-571 

Bacillus   of   Friedlander   and   Other  Members   of 

the  Capsule-Forming  Group 571-572 

Chapter  XXVII. 

Group    IV. — Chronic   Infections    in    Which    Lasting 

Immunity  is  Not  Established. 

Tuberculosis     573-615 

Leprosy     615-623 

Glanders     623-629 

Rhinoscleronia    629 

Actinomycosis    629-633 


CONTENTS.  XV 

Madura    Foot 633-634 

Infections      by      Streptothrix,      Cladothrix      and 

Leptothrix    634-635 

Oidiomycosis    635-641 

Chapter  XXVIII. 
Group  V. — Diseases  Due  to  Spirilla. 

Relapsing  Fever 642-646 

Syphillis     646-652 

Frambesia     652 

Other    Spirochetes 653 

Chapter  XXIX. 
Group   VI. — Protozoon   Infections. 

Malaria     654-670 

Trypanosomiasis   670-684 

Texas    Fever 684-686 

Amebic   Dysentery 686-690 

Sarcosporidia     690-691 

Balantidium  Coli 691-692 

Cercomonas  Intestinalis 692-693 

Trichomonas 693-694 

Coccidiosis    694-695 

Kala-Azar    696 

Chapter  XXX. 

Group  VII. — Diseases  of  Doubtful  or  Unknown 
Origin. 

Hydrophobia    697-710 

Yellow    Fever 711-720 

"Spotted  Fever"  of  the  Rocky  Mountain  States .  .  720-725 

Typhus   Fever 725-728 

Dengue  Fever 728-729 

Acute  Articular  Rheumatism 729 

Smallpox  and   Vaccinia 729-743 

Chickenpox    (Varicella ) 743-744 

Scarlet    Fever 744.747 

Measles   747-750 

German  Measles   ( Rotheln ) 750 

Whooping  Cough 750-755 

Mumps    755-756 

Epidemic  Poliomyelitis 756-758 

Noma    758-759 


INTRO'DUCTION 


HISTORICAL  AND   DEVELOPMENTAL. 

The  conception  of  the  nature  of  immunity  Early  Times 
which  was  current  at  one  period  or  another  of  ticesr*****^" 
history  had  some  relationship  to  the  conception 
of  the  etiology  of  diseases  at  those  times.  It  will 
be  remembered  that  at  one  time  diseases  were 
supposed  to  be  imposed  by  an  angry  deity,  and  to 
avert  them  various  mysticisms  were  resorted  to^ 
such  as  the  utterance  of  incantations  and  the 
wearing  of  talismans.  On  the  other  hand,  a  more 
logical  attempt  to  explain  the  natural  immunit}' 
of  the  Psylli  against  snake  poison  was  made  by 
Pliny,  who  suggested  that  it  might  be  due  to  their 
habit  of  drinking  water  from  wells  in  which  pois- 
onous snakes  dwelt.  This  is  not  unlike  our  pres- 
ent conception  of  active  immunization. 

Von  Behring  quotes  literature  to  show  that 
among  some  primitive  races  of  to-day,  artificial 
immunization  is  carried  on;  a  Mozambique  tribe 
is  said  to  inoculate  against  snake  poison  by  rub- 
bing into  a  small  cutaneous  incision  a  paste  which 
contains  venom.  Probably  non-fatal  quantities 
are  introduced  in  this  way,  resulting  in  the  forma- 
tion of  venom  antitoxin,  a  method  comparable  to 
that  used  in  the  production  of  diphtheria  anti- 
toxin. 

At  a  very  early  period  the  possibility  of  habitua- 
tion to  poisonous  drugs  was  recognized.  We  learn 
that  Mithridates  by  taking  gradually  increasing 
doses  of  poisons  established  in  himself  resistance 


2  INFECTION    AND    IMMUNITY. 

of  this  sort.  It  is  stated  also  that  he  fed  ducks 
with  poisons  and  then  proposed  to  use  their  blood 
as  an  antidote  (serum  therapy).  The  importance 
of  antidotes  in  the  minds  of  the  ancients  may  be 
appreciated  from  the  fact  that  epidemic  diseases, 
such  as  plague,  cholera  and  smallpox,  were  at  one 
time  considered  as  due  to  unknown  poisons,  which 
might  be  comparable  in  nature  to  some  known 
poisons,  as  aconite.  Mercury  for  syphilis,  quinin 
for  malaria,  and  salicylic  acid  for  rheumatism 
would  certainly  have  fallen  into  the  category  of 
antidotes,  and  mercury  may  have  been  so  con- 
sidered. 

A  historic  illustration  of  the  treatment  of  dis- 
ease on  a  supposed  etiologic  basis  is  found  in  a 
theory  which  was  prevalent  in  the  seventeenth 
century,  according  to  which  diseases  were  either 
acid  or  basic  in  character,  and  hence  should  be 
treated,  the  one  with  an  alkali,  the  other  with  an 
acid.  Sylvius  considered  plague  to  be  of  acid 
nature  and  administered  alkalies,  while  Etmiiller 
took  the  opposite  view. 

Manifestly,  rational  treatment  and  prophylaxis 
of  the  infectious  diseases  could  not  be  undertaken 
until  their  etiology  was  correctly  understood.  Yet 
here,  as  so  often  happens  in  medicine,  empiricism 
preceded  rationalism.  For  example,  protective 
inoculation  did  not  become  a  principle  until  the 
time  of  Pasteur,  yet  it  had  been  practiced  against 
smallpox  for  centuries,  and  the  method  put  on 
its  present  basis  by  Jenner  long  before  there  was 
any  idea  as  to  the  principles  involved  in  the  pro- 
tection. 
Micro-  The  belief  that  invisible  "animalcules"  are  able 
to  cause  morbid  processes  m  man  is  a  very  old 


TEE   MICROSCOPE.  3 

one.  A  passage  from  Varro  (116-27  B.  C.)  reads 
as  follows:  "There  are  swampy  places  in  which 
grow  animals  never  so  small  which  may  not  be 
recognized  by  the  eye,  and  which  gain  access  to  the 
body  through  the  air  and  bring  about  severe 
diseases.'*^ 

The  discovery  and  use  of  the  compound  micro-  The 
scope  in  the  seventeenth  century  disclosed  the 
reality  of  the  minute  living  forms  which  had  been 
suspected  so  often.  Kircher,  with  his  first  crude 
microscope  (1646),  examined  the  tissues  of  va- 
rious diseases,  and  was  the  author  of  many  the- 
ories as  to  their  etiology.  It  is  now  believed  that 
the  magnification  of  Kircher's  microscope  was  so 
small  that  many  of  the  "worms"  which  he  saw 
were  really  larger  fungous  cells  and  in  some  in- 
stances the  as  yet  unidentified  blood  and  pus  cells. 

Leeuwenhoek  (1632-1723),  a  Dutch  naturalist, 
with  his  compound  microscope  magnifying  1,000 
diameters,  observed  accurately  many  microscopic 
forms,  but  made  no  application  of  his  discoveries 
to  medical  problems;  nevertheless,  such  applica- 
tion was  not  wanting,  and  the  succeeding  century 
and  a  half  saw  such  voluminous  descriptions  of 
microbes,  so  many  contradictory  theories  and 
statements  concerning  their  relationship  to  in- 
fections, that  the  "infinitesimally  smalP'  fell  into 
disfavor  in  many  quarters  as  the  causes  of  diseases. 
The  attractions  and  reasonableness  of  the  theory, 
however,  were  such  that  it  continued  to  gain  ex- 
ponents, and  in  the  early  part  of  the  nineteenth 
century  reached  a  degree  of  definiteness.  In  1855, 
the  great  French  physician,  Bretonneau,  afiirmed 
that  a  specific  germ  was  the  cause  of  every  con- 


Microscope, 


INFECTION    AND    IMMUNITY. 


Anthrax. 


Fernienta- 
tions. 


Mlcrolilo 
Specificity,    jtv 


tagious  disease:  "An  epidemic  disease  can  orig- 
inate and  extend  only  through  the  agency  of  the 
germ  producing  it."  Yet  at  this  time  no  infec- 
tion had  been  definitely  proved  to  be  of  microbic 
origin. 

In  1850  Raver  and  Devaine  made  an  observa- 
tion, which  might  have  fallen  into  the  oblivion  of 
many  preceding  ones  had  it  not  been  confirmed  by 
later  investigators.  They  found  "small  filiform 
bodies"  in  the  blood  of  sheep  which  had  died  of 
anthrax,  and  were  naturally  inclined  to  believe 
that  these  forms  caused  the  disease.  Other  scien- 
tists, especially  Pasteur  and  Koch,  soon  took  up 
the  study  of  anthrax,  with  the  result  that  the 
small  rods  of  Devaine  were  scientifically  proved  to 
be  its  cause. 

Tw^o  great  minds  dominated  medical  research 
at  this  time — Pasteur  and  Koch.  Pasteur,  in  his 
early  career  as  a  chemist,  had  had  his  attention 
called  to  the  processes  of  fermentation.  He  re- 
curred to  this  subject  at  a  time  when  the  theory 
of  the  spontaneous  generation  of  small  living 
form>^  was  widely  discussed,  and  in  1857-1861 
proved  beyond  any  possibility  of  doubt  that  lactic 
acid,  alcoholic  and  butyric  acid  fermentations  are 
due  to  the  action  of  minute  living  cells;  and,  fur- 
thermore, that  each  particular  kind  of  fermenta- 
tion has  its  own  peculiar  microbe  as  the  cause. 
This  was  an  example  of  what  we  term  to-day  mi- 
crobic specificity,  in  marked  contrast  to  views 
which  were  then  prevalent  regarding  the  variabil- 

Pasteur   then   applied 


of  micro-organisms.* 


*  "Thp  followlnj?  citation  from  NSgell  Illustrates  clearly 
this  Idoa  of  nnlimlfpd  variability  of  microbes :  'In  the 
coiirso  of  Kf'nf'ations  the  same  speclos  assumes  alternat 
Ingly  different  morpholojjkal  and  physiological  forms  which, 
as    years    and    periods    of    years    pass    by,    may    canse    now 


VACCINATION.  5 

what  he  had  learned  about  fermentations  to  the 
study  of  the  diseases  of  wines  and  beers»  He  found 
their  causes,  and  devised  a  preventive  measure, 
which  consisted  merely  in  the  destruction  of  the 
germs  by  heating  the  wine  to  a  suitable  tempera- 
ture before  it  was  stored.  At  the  instance  of  the 
French  government,  he  then  studied  certain  dis- 
eases of  silkworms.  His  success  in  discovering 
their  causes  and  prevention  must  always  remain  for 
us  one  of  the  landmarks  of  the  world's  progress. 
It  was  during  the  latter  investigations  that  he 
took  up  the  study  of  anthrax.  The  specific  mi- 
crobe having  been  discovered,  and  the  methods  of 
transmission  of  the  malady  having  been  made 
clear  through  investigations  by  both  Pasteur  and 
Koch,  Pasteur  turned  his  attention  to  methods 
of  prevention  and,  if  possible,  of  cure. 

Pasteur  pondered  the  question  of  smallpox  vac-  vaccina- 
cination.  He  came  to  believe  that  vaccinia  is 
smallpox,  the  virus  of  which  has  been  attenuated 
by  its  passage  through  the  cow,  and  that  conse- 
quently when  man  undergoes  vaccination  he  there- 
by is  inoculated  with  a  benign  form  of  the  disease. 
Might  not  this  be  an  example  of  a  law  which  would 
be  general  in  its  application  ?  The  protective  inoc- 
ulation (active  immunization)  against  the  pleuro- 
pneumonia of  cattle  which  had  long  been  prac- 
ticed gave  encouragement  to  this  hope.  Some 
work  by  Toussaint  was  important  in  the  answer 
to  this  question.  It  was  evident  that  a  weakening 
or  attenuation  of  the  bacteria  or  virus  must  first 

souring  of  milk,  now  the  formation  of  butyric  acid  in  sauer- 
kraut, now  the  fermentation  of  wine,  now  the  decomposition 
of  albuminous  matters,  now  the  splitting  up  of  urea,  now 
the  red  color  of  starchy  food,  and  give  rise  now  to  diphtheria, 
now  to  typhoid  fever,  now  to  recurrent  fever,  now  to 
cholera,  now  to  malarial  fever.'  "  (Cited  from  Hektoen,  in 
Osier's  System  of  Modern  Medicine,  Vol.  I.) 


6  INFECTION    AND    IMMUNITY. 

be  obtained  before  it  could  be  safely  injected  into 
animals  for  the  purpose  of  producing  immunity, 
for  if  the  unaltered  virus  were  injected  the  viru- 
Antiirax.  lent  iufcction  would  result.  Accordingly,  Tous- 
saint  heated  the  blood  of  a  sheep  which  had  died 
of  anthrax,  to  a  temperature  of  55°  C.  for  ten 
minutes,  then  injected  it  into  a  number  of  sheep. 
Some  of  the  animals  died  of  anthrax,  while  others 
suffered  only  a  mild  attack  from  which  they  re- 
covered; the  latter  were  found  to  be  immune  to 
a  subsequent  inoculation  with  virulent  blood.  In- 
asmuch, however,  as  some  of  Toussaint's  animals 
had  died  of  anthrax,  Pasteur  concluded  that  there 
was  some  grave  error  in  technic.  He  considered 
that  Toussaint's  method  probably  killed  or  atten- 
uated the  fully-developed  bacilli,  but  did  not  in- 
jure the  spores  of  the  parasite  (Koch  had  pre- 
viously shown  the  existence  of  anthrax  spores). 
After  much  experimentation,  Pasteur  hit  on  the 
plan  of  growing  the  bacillus  at  a  temperature  of 
42°  C,  obtaining  in  this  way  a  culture  of  the 
fully  developed  organism  which  had  a  low  viru- 
lence, but  which  did  not  form  the  dangerous 
spores.  When  sheep  were  inoculated  with  the 
proper  amount  of  this  culture,  which  became 
known  as  anthrax  vaccine,  they  had  a  mild  attack 
of  the  disease,  which  rendered  them  immune  to 
virulent  inoculations. 
Hydro-  With  the  possibility  of  protective  inoculation 
phoiiin.  ^^-^1^  ^  known  virus  actually  demonstrated,  sim- 
ilar procedures  were  tried  with  other  animal  dis- 
eases of  known  bacterial  etiology,  with  the  result 
that  successful  vaccines  against  chicken  cholera 
and  swine  plague  were  developed.  Somewhat 
later,  having  failed  in  their  attempts  to  discover 


THEORIES    OF   IMMUNITY.  7 

the  microbes  of  plague  and  cholera,  Pasteur  and 
his  co-workers  turned  to  the  study  of  hydropho- 
bia. All  efforts  to  cultivate  the  virus  from  the 
spinal  cord  of  rabid  dogs  failed,  although  inocula- 
tion experiments  proved  its  presence  in  this  struc- 
ture. The  unique  idea  then  occurred  to  consider 
the  infected  spinal  cord  as  a  fully  developed  cul- 
ture of  the  virus.  It  remained  to  subject  such  a 
culture  to  the  proper  attenuating  conditions  for 
the  purpose  of  weakening  or  actually  destroying  its 
virulence  in  order  to  make  it  fit  for  protective  in- 
jections. This  was  accomplished  by  drying  the 
cords  in  a  closed  vessel  over  a  hygroscopic  sub- 
stance (solid  potassium  h3'droxid),  the  final  viru- 
lence of  the  cord  depending  on  the  length  of  time 
it  had  been  subjected  to  the  drying  process.  The 
technic  of  the  protective  injections,  the  success  of 
which  is  household  knowledge,  will  be  a  subject  for 
later  consideration. 

Of  primary  importance,  during  this  period,  was  ttvo 
the  w^ork  of  Koch  on  the  specific  bacteria  of  tu-  p*I?i^*IS^es. 
berculosis,  cholera,  typhoid  and  the  pyogenic  dis- 
eases; and  not  least  his  improved  methods  of  ob- 
taining pure  cultures  through  the  "use  of  solid 
media  (gelatin)  on  plates.  Through  his  work  and 
that  of  Pasteur  two  great  principles  had  been 
set  in  motion ;  the  microbic  specificity  of  infectious 
diseases,  and  protective  inoculation  in  its  general- 
ized form,  through  the  "use  of  attenuated  virus. 

The  scientific  mind  turned  at  once  to  the  in-  Theories  of 
quiry.  What  changes  in  an  animal  body  are  re-  of  immnnity. 
sponsible  for  the  immunity  which  is  acquired  as 
the  result  of  protective  inoculations?     Also,  upon 
what  properties  of  the  tissues  or  body  fluids  does 
the  natural  immunity  of  an  animal  depend,  and 


8  IXFECTIOX    AXD    IMMUyiTY. 

cxiianstion  cloes  the  susceptibilitj  of  one  species  depend  on 
Theory.  ^|^g  absencc  of  those  properties  which  characterize 
the  natural  immunity  of  another  species?  Pas- 
teur had  observed  that  if  he  grew  the  microbe  of 
chicken  cholera  in  a  liquid  medium  for  some  time, 
then  removed  the  bacteria  by  filtration,  the  fluid 
became  unfit  for  the  further  growth  of  the  organ- 
ism on  subsequent  reinoculation.  That  is,  the 
nutrient  material  had  been  used  up;  and  he  sug- 
gested that  this  is  the  case  in  the  body  of  an  ani- 
mal. Having  undergone  the  infection,  suitable 
nutrient  material  for  the  microbe  is  used  up,  and 
recovery  ensues.  The  prolonged  absence  of  the 
proper  nutritious  substances  would  account  for 
the  more  or  less  permanent  nature  of  the  acquired 
immunity.  This  conception,  the  exhaustion 
theory,  at  one  time  shared  by  Koch  and  Klebs,  is 
still  represented  in  an  altered  form  by  Baumgar- 
ten,  who  speaks  of  an  unfavorable  culture  medium 
as  representing  the  condition  of  the  immune  body, 
which,  of  course,  is  broadly  true. 
\oxionN  Chauveau  was  the  author  of  another  historic 
^T?ieo*ry!  thcory  of  acquired  immunity  (the  noxious  reten- 
tion theory),  which  maintained  that  during  the 
course  of  a  disease  the  bacteria  produce  substances 
in  the  presence  of  which  they  can  not  develop 
further;  consequently  recovery  takes  place,  and 
the  continued  presence  of  these  noxious  substances 
renders  another  attack  of  the  disease  impossible. 
Although  it  is  true  that  bacteria  do  not  grow  well 
in  their  own  metabolic  products,  theories  of  im- 
munity on  this  and  similar  bases  arc  not  in  ac- 
cord with  the  fact  that  immunity  may  be  of  great 
duration,   and    that  it   may   be  conferred  by  the 


rROI'EUTIE^    OF    SERUMS.  9 

injection  of  the  killed  bacteria;,  or,  in  some  cases, 
of  their  non-living  soluble  products. 

Metchnikoff  mav  be  credited  with  having  first  Fnagoc^- 
offered  a  plausible  explanation  of  natural  resist- 
ance, founded  on  observation.  As  a  zoologist  he 
had  studied  the  subject  of  intracellular  digestion 
in  the  lower  animals,  and  it  was  while  working  on 
this  problem  that  he  observed  the  fate  of  a  yeast 
fungus  {Monospora),  which  caused  epidemics 
among  the  daphnia,  small,  transparent  animals 
with  which  he  was  working.  iSTear  the  alimentary 
tract,  which  was  the  infection  atrium,  some  large 
mesoblastic  cells,  which  are  perhaps  analogous  to 
the  white  blood  cells,  were  seen  to  ingest  the  para- 
sites and  dissolve  them.  If  this  took  place  to  a 
sufficient  extent  the  animals  recovered;  if,  how- 
ever, the  infecting  organisms  were  too  numerous 
or  the  reaction  on  the  part  of  the  animal  insuffi- 
cient, the  body  became  overwhelmed  with  para- 
sites and  death  resulted.  Since  that  time  Metch- 
nikoff  has  evolved  his  well-known  theory  of  pha- 
gocytosis as  the  essential  factor  in  both  natural 
and  acquired  immunity,  a  theory  which  Pasteur, 
in  his  later  years,  looked  on  with  favor.  We  may 
speak  of  this  as  the  cellular  theory  of  immunity; 
a  theory  which  has  had  to  undergo  important 
modications  in  order  to  bring  it  into  accord  with 
new  facts. 

Considering  that  natural  or  acquired  immunity  investisa- 
must  exist  because  of  certain  qualities  of  the  body  p^  "pertiis^ 
cells,  or  of  the  body  fluids,  or  possibly  of  both,  of  serums. 
investigators  began  to  make  analyses  of  the  tis- 
sues; and  of  all  the  analyses,  that  which  we  may 
term  the  biologic  has  been  the  most  fruitful.     In 
this  case  biolos^ic  analvsis  means  the  detection  of 


10  IXFECTKjy    AXD    IMMUXITY. 

reactions  which  may  occur  when  bacteria  or  their 
products  are  placed  in  contact  with  tissue  cells 
or  fluids,  either  in  the  living  animal  or  in  test- 
glass  experiments.  The  chief  of  these  are  the  de- 
Bacterici-  termination  of  the  ability  of  the  serum  of  an  ani- 
ower.  ^^^^  ^^   ^^-^^  bacteria  or  to    neutralize    bacterial 

toxins.  These  important  investigations  were  in- 
augurated by  the  findings  of  Fodor,  Nuttall,  Nis- 
sen,  V.  Behring  and  Buchner,  which  showed 
that  fresh  defibrinated  blood,  and  the  blood 
serum  of  various  animals,  are  able  to  kill  bac- 
teria in  the  reagent  glass.  In  contrast  to  the 
action  of  ordinary  antiseptics,  this  power  is 
often  selective,  killing  one  variety  of  bacterium 
and  leaving  another  unharmed.  This  was  of  enor- 
mous importance,  as  it  seemed  to  identify  the 
factor  on  which  natural  antibacterial  immunity 
depends.  Then  followed  the  discovery  of  Nissen 
and  V.  Behring  (Vibrio  metchniJcovi) ,  and  of 
Bouchard  (B.  pyocyaneus),  that  if  an  animal  is 
systematically  injected,  i.  e.,  immunized,  with  a 
micro-organism,  the  power  of  its  serum  to  kill 
the  bacterium  used  in  the  immunization  is  greatly 
increased ;  from  which  it  would  seem  that  acquired 
immunity  depends  on  the  increase  of  powers  which 
are  normally  present  to  a  certain  degree.  These 
observations  have  to  do  with  the  bactericidal  power 
of  serum. 
ToxiiiM  and  Further  progress  was  made  through  the  discov- 
eries that  the  tetanus  bacillus  (Brieger  and  Friin- 
kel)  and  the  diphtheria  bacillus  (Roux  and  Yer- 
sin)  secrete  each  a  powerful,  speciilc,  soluble  toxin, 
which  may  be  separated  from  the  bacteria  by  fil- 
tration. Immunization  with  these  bacterium-free 
toxins   was   undertaken    (Behring   and    Kitasato, 


TOXINS    AND    ANTITOXINS.  11 

1890)  with  the  familiar  result  of  the  production 
of  the  specific  antitoxins.  Other  investigations  in 
this  direction  soon  showed  the  independence  of 
the  antibacterial  and  the  antitoxic  properties  of 
serums. 

With  these  facts  in  hand,  the  vigor  with  which 
investigations  have  been  pushed  may  be  readily 
imagined.  The  hope  naturally  prevailed  that  phy- 
sicians might  become  the  masters  of  all  infectious 
diseases,  through  the  possession  of  specific  anti- 
bacterial and  antitoxic  serums.  But  failures,  with 
which  we  are  only  too  familiar,  met  the  attempts 
to  produce  adequate  antiserums  for  many  diseases. 
Nevertheless  these  failures,  through  stimulation 
to  closer  study,  have  resulted  in  the  accumulation 
of  much  additional  knowledge  concerning  the 
pathogenic  properties  of  different  bacteria,,  the 
nature  of  the  immune  serums  and  the  various  pro- 
tective factors  of  the  bodv.  Ehrlich  has  evolved 
a  new  theory  of  immunity  from  facts  which  were 
discovered  in  his  laboratory,  the  "side-chain" 
theory,  which  it  is  the  purpose  to  utilize  in  the 
interpretation  of  many  reactions  which  will  come 
up  for  consideration. 

W'^right  in  England,  Neufeld  in  Germany,  and 
Hektoen  in  America  more  recently  have  led  in  a 
revival  of  interest  in  phagocytosis  as  a  factor  in 
natural  and  acquired  immunit}^,  with  the  result 
that  there  can  no  longer  exist  any  doubt  that  pha- 
gocytosis plays  an  important  role  in  protection 
against  and  in  recovery  from  many  infections. 
Thus  the  opsonins  of  Wright,  and  the  bacterio- 
tropic  substances  of  Neufeld,  have  served  to  bridge 
any  chasm — never  a  real  chasm — which  seemed  to 
exist  between  the  so-called  humoral  and  cellular 


12  INFECTION    AND    IMMUNITY. 

theories  of  immunity.  The  study  of  opsonins  has 
also  served  to  renew  interest  in  a  much-neglected 
field  of  specific  prevention,  namely,  bacterial  vac- 
cination, one  of  the  most  gratifying  results  of 
which  has  been  a  return  to  the  tuberculin  therapy 
of  Koch. 

However,  with  all  our  resourcefulness,  it  is  pos- 
sible that  our  limitations  may  soon  be  reached  re- 
garding the  serum  and  vaccinal  therapy  of  many 
infections,  and  we  shall  be  forced  to  try  other  prin- 
ciples of  prevention  and  cure.  In  connection  with 
this  point,  the  newer  chemotherapy,  which  has 
been  developed  in  so  brilliant  a  manner  by  Ehr- 
lich  and  others  in  relation  to  trypanosomiasis,  is 
of  the  highest  interest.  It  may  be  hoped  that  this 
work  represents  only  the  beginning  of  a  new  direc- 
tion of  research,  which  will  be  of  ultimate  value  in 
various  bacterial  as  well  as  protozoan  infections. 


PART  ONE 
PRINCIPLES  OF  INFECTION. 


CHAPTEE  I. 


Disease. 


PARASITISM,    INFECTIOUSNESS,    CONTAGIOUSNESS. 

Parasitism  is  the  condition  in  which  a  plant,  or  parasitii 
an  animal  being,  lives  on  or  within  another  living 
organism.    A  true  parasite  always  derives  its  sus- 
tenance from  the  tissues  of  its  host. 

An  infectious  disease  is  one  which  is  caused  by  infectious 
living  organisms  which  in  some  way  have  entered 
the  body,  where  they  multiply  and  liberate  poison- 
ous substances.  Accordingly  the  word  has  refer- 
ence to  the  nature  of  the  cause  of  the  disease.  It 
is  from  the  Latin  inficere,  meaning  to  place  in  or 
into. 

Some  parasites  may  live  on  a  host  without 
causing  appreciable  damage;  they  are  non-patho- 
genic parasites.  In  this  case  they  may  derive 
their  nutrition  from  some  of  the  excreted  non-liv- 
ing products  of  the  host,  living  as  pure  sapro- 
phytes/ or  the  amount  of  nutritious  substance 
which  they  obtain  from  the  host  may  be  so  little 
that  the  health  of  the  latter  is  not  impaired.  This 
is  true  of  organisms  which  normally  inhabit  the 
intestinal  tract. 

1.  A  saprophyte  is  defined  as  a  vegetable  organism 
which  lives  on  dead  organic  matter.  An  organism  which  is 
habitually  saprophytic  may  become  .pathogenic  under  the 
proper  conditions  (bacillus  of  malignant  edema).  And,  od 
the  other  hand,  a  pathogenic  parasite  lives  a  saprophytic 
life,  when  it  grows  in  our  artificial  culture  media. 


14 


INFECTION    AND    IMMUNITY. 


Infestation 
and    Infec- 
tion. 


Bactcrin       nnd 
ProtoKon. 


There  is  another  large  class  of  parasites,  how- 
ever, which  under  proper  conditions  cause  severe 
diseases  in  the  host.  Many  pathogenic  microbes  live 
in  and  on  the  skin  and  mucous  membranes  with- 
out doing-  harm,  but  if  certain  ones  reach  the 
deeper  tissues,  they  may  institute  pathoh^gic  proc- 
esses (e.  g.,  staphylococci,  streptococci,  pneumococ- 
ci,  diphtheria  bacilli  and  meningococci).  Any  or- 
ganism which  is  able  to  cause  pathologic  tissue 
changes,  to  disturb  functions,  and  to  set  up  ab- 
normal symptoms  is  classed  as  a  pathogenic  para- 
site. The  abnormal  processes  which  they  institute 
are  our  infectious  diseases. 

Where  certain  comparatively  large  organisms 
(macroparasites)  exist  on  a  body  surface,  as  the 
skin  or  intestinal  tract,  the  surface  is  said  to  be 
infested;  tlie  skin,  for  example,  is  infested  with 
pediculi.  One  may  also  say  that  the  intestinal 
tract  is  infested  with  tapeworms,  but  here  the  dis- 
tinction between  infestation  and  infection  is  not  to 
be  drawn  so  sharply;  surely  when  the  larvae  pene- 
trate the  intestinal  wall  and  reach  the  circulation 
or  distant  organs  we  must  speak  of  infection.  But 
even  the  adult  tenia  as  it  exists  in  the  intestines 
may  cause  erosions  of  the  mucous  membrane  or 
may  perhaps  burrow  a  slight  distance  into  the 
wall,  a  condition  which  approximates  the  action  of 
the  larva?  in  passing  through  the  wall;  accordingly 
at  some  point  the  distinction  between  infestation 
and  infection  becomes  an  arbitrary  one. 

The  known  pathogenic  micro-organisms  are 
grouped  among  the  fungi,  the  l)acteria  and  the  pro- 
tozoa. Both  the  l)acteria  and  fungi  are  vegetable 
in  nature,  complexity  in  form  and  methods  of 
growth  characterizing  the  latter,  whereas  the  life 


BACTERIA    AyD     PROTOZOA.  15 

history  of  the  former  is  simpler,  and  they  multi- 
ply only  by  fission  (fission  fungi).  Forms  occur 
which  appear  to  be  intermediate  between  the  true 
fungi  and  the  true  bacteria.  The  protozoa,  the 
lowest  forms  of  animal  life,  vary  greatly  in  form 
and  in  the  complexity  of  their  life  cycles.  The 
highest  protozoa  lead  an  intricate  existence  in 
which  sexuality  and  alternation  of  hosts  are  some- 
times conspicuous  features,  as  in  the  case  of  the 
parasites  of  malarial  fevers,  and  possibly  in  that  of 
yellow  fever.  In  some  instances  the  alternation 
of  hosts  is  purely  a  facultative  property,  and  not  a 
necessity  for  the  perpetuation  of  the  species,  al- 
though it  is  part  of  the  natural  cycle;  this  is  the 
case  with  some  of  the  trypanosomes,  which  can  be 
transferred  from  animal  to  animal  artificially  for 
an  indefinite  period. 

There  are  certain  infections,  the  causes  of  which 
are  not  known,  and  in  some  instances  the  organ- 
isms are  considered  as  ultramicroscopic  because 
they  pass  through  bacteriologic  filters.  Theoretic- 
ally they  may  be  either  bacteria  or  protozoa. 

The  known  pathogenic  micro-organisms  may  Types  of^^Mi- 
also  be  placed  in  one  of  the  following  three  groups : 
1.  Obligate  parasites,  which  are  capable  of  growth 
only  in  a  living  organism  (the  bacillus  of  leprosy 
and  the  organisms  of  malaria).  2.  Facultative 
saprophytes,  which  usually  exist  as  parasites  but 
may  multiply  on  inanimate  material  under  proper 
conditions.  This  group  includes  most  of  the  path- 
ogenic microparasites.  3.  Facultative  parasites, 
which  are  saprophytic  organisms  living  readily  on 
inanimate  material,  but  which  may  produce  dis- 
ease when  thev  reach  suitable  tissues  in   a  host 


cro-para  sites. 


iNniN. 


16  INFECTION    AND    IMMUNITY. 

{Bacillus  tdani,  bacillus  of  malignant  edema, 
Amwha  dy sentence) . 
Origin  and  It  is  futilc  to  Speculate  on  the  ultimate  origin  of 
in  orj^nn-  oui'  various  micro-organisms.  It  is  sufficient  to 
appreciate  that  the  principles  of  biology  and  evolu- 
tion are  broad  enough  to  permit  us  to  assume  that 
some  of  the  species  which  we  now  recognize  may 
have  arisen  through  the  influences  of  environment 
and  selection  from  other  more  or  less  closely  re- 
lated species.  However,  investigations  have  shown 
that  the  essential  characters  of  bacterial  species  are 
fixed  more  or  less  fimily,  suggesting  that  new  spe- 
cies are  likely  to  be  developed  only  through  a  long 
course  of  time,  or.  if  more  quickly,  through  rare 
chance  variations.  Koch  has  suggested  that  among 
the  trypanosomes  found  in  different  diseases  some 
may  still  be  too  young  in  their  differentiation  to 
represent  fixed  species,  although  this  cannot  apply 
to  the  whole  group  of  tiypanosomes. 

Many  micro-organisms  do,  indeed,  show  a  great 
deal  of  flexibility  in  their  physiology  and  viru- 
lence, with  the  result  that  they  may  approximate 
species  which  are  usually  recognized  as  being  dis- 
tinct. Thus  a  strain  of  the  diphtheria  bacillus 
which  loses  its  virulence  is  similar  to  a  pseudo- 
diphtheria  bacillus,  and  the  cholera  vibrio  which 
has  become  avirulent  resembles  a  number  of  other 
vibrios.  The  plague  bacillus,  whereas  it  commonly 
causes  acute  death  in  rats,  may  undergo  such  a 
change  in  the  character  of  its  virulence  that  it 
causes  a  chronic  nodular  inflammation.  Some 
strains  of  the  tetanus  bacillus,  which  is  habitually 
anaerobic,  acquire  the  power  of  growing  in  the 
presence  of  atmospheric  oxygen.  By  suitable 
passage  a  species  of  the  tubercle  bacillus  may  be 


VARIETIES    OF   ORGANISMS.  17 

made  to  resemble  very  closely  in  its  cultural  as- 
pects another  species  of  this  organism.  On  the 
whole,  these  are  not  large  variations,  and  identifi- 
cation can  be  accomplished  by  one  or  more  of  the 
biologic  reactions,  such  as  the  agglutination,  bac- 
teriolytic or  opsonic  tests. 

In  some  instances  the  conditions  are  such  that  varieties. 
different  species  appear  to  represent  only  differ- 
ent grades  or  types  of  virulence  of  the  same  or- 
ganism. Those  acid-fast  bacilli  which  resemble 
the  bacillus  of  tuberculosis  form  the  most  striking 
example  of  this.  Bacilli  of  this  character  are  com- 
monly found  in  various  grasses  or  clover,  which 
are  used  as  food  by  cattle.  Such  organisms  have 
a  low  grade  *of  virulence,  and  when  injected  into 
animals  cause  the  formation  of  only  a  nodule  of 
granulation  tissue,  sometimes  with  the  presence 
of  giant  cells,  and  the  process  heals  readily.  It  is 
possible  that  certain  of  these  organisms  of  more 
than  usual  virulence,  or  which  may  have  acquired 
such  virulence  by  residence  in  the  alimentary  tract 
of  the  ox,  have  retained  their  new  pathogenic 
power  as  a  permanent  character,  and  that  bovine 
tuberculosis  originated  in  this  way.  It  would  be 
none  the  less  logical  to  assume  that  the  bacillus 
of  human  tuberculosis  was  derived  from  the  bo- 
vine type  in  a  similar  manner.  This  can  only  be 
a  subject  for  speculation,  however. 

Bacteriologists  frequently  are  able  to  place  a 
number  of  species  in  a  "group,"  the  members  of 
'  which  resemble  each  other  more  or  less  closely,  as 
the  colon  group,  or  the  dysentery  group.  The 
members  of  a  group  may  ysltj  widely  in  their 
pathogenic  power,  whereas  in  other  instances  they 
produce  similar  diseases.     Thus,  ^ovy  has  shown 


18  INFECTION    AND    IMMUNITY. 

that,  although  the  spirilla  which  cause  the  various 
relapsing  fevers  are  very  similar,  they  can  be  dif- 
ferentiated by  means  of  immunity  reactions,  such 
as  the  agglutinating  or  protective  powers  of  im- 
mune serums. 

A  more  detailed  discussion  of  this  aspect  of 
general  bacteriology  would  carry  us  too  far  afield. 
"Infectious"  Confusion  sometimes  arises  concerning  the  sig- 
*?aKions""  nificancc  of  the  words  infectious  and  contagious 
and  other  words  having  similar  roots.  This  con- 
fusion is  due  in  large  part  to  the  fact  that  they 
have  grown  into  a  usage  varying  somewhat  from 
that  which  originally  adhered  to  them,  and  the 
dictionaries,  even  those  which  are  medical  in  char- 
acter, have  hardly  kept  pace  with  the  transition. 

The  significance  of  infectious  is  indicated  in  the 
definition  of  an  infectious  disease  as  given  above. 
The  word  contagious,  on  the  other  hand,  relates 
to  a  method  by  which  some  of  the  infectious  dis- 
eases are  transmitted  from  an  infected  person  or 
animal  to  the  healthy,  namely,  contact,  direct  or 
indirect.  Not  all  infections  are  transmitted  by 
contact,  however,  hence  we  may  divide  them  into 
those  which  are  contagious  and  those  which  are 
not.  Communicable  is  often  used  as  synonymous 
with  contagious. 

Contniriousncss  is  all  the  more  striking  in  the 
case  of  acute  infections  which  develop  rapidly  and 
soon  after  exposure.  On  the  other  hand,  it  is  not 
so  stnking  in  a  disease  such  as  pulmonary  tuber- 
culosis, which  develops  slowly  and  perhaps  only 
after  repeated  exposures. 

The  following  rather  general  arrangement  of 
the  infectious  diseases  into  groups  according  to 
the  methods,   and    at   the   same  time  facility,  of 


DISSEMINATION    OF    ORGANISMS. 


19 


transmission  is  given   in  order  to   illustrate   the 
idea  and  limits  of  contagiousness. 

1.  Those  which  are  characterized  by  ready  trans- 
mission through  the  air.  The  micro-organisms  are 
discharged  into  the  air  from  the  respiratory 
passages,  or  from  the  skin  in  desquamative  infec- 
tions, and  it  is  only  necessary  for  a  susceptible 
person  to  come  within  the  zone  of  infected  air 
which  surrounds  the  patient  in  order  to  acquire 
the  disease.  Actual  contact  with  the  patient  may 
facilitate  transmission  in  some  instances,  but  is 
not  necessary,  and  many  of  them  are  transmitted 
by  indirect  contact,  i.  e.,  through  the  agency  of 
intermediate  persons,  through  food  contamination 
(scarlet  fever  in  milk),  or  through  inanimate  sub- 
stances which  have  been  in  contact  with  the  pa- 
tient. These  are  all  highly  contagious  "air-borne" 
diseases,  which  probably  use  the  respiratory  pas- 
sages as  their  infection  atrium.  Diphtheria,  scar- 
let fever,  measles,  rotheln,  smallpox,  influenza,  tu- 
berculosis, and  plague  in  plague  pneumonia  are  of 
this  type. 

2.  Transmission  occurs  almost  exclusively  by 
personal  contact,  and  usually  a  special  form  of 
contact,  never  through  the  air:  gonorrhea,  syph- 
ilis, soft  chancre,  and  perhaps  dourine  in  horses. 
Syphilis  occasionally  is  transmitted  by  indirect 
contact,  the  free  period  being  a  short  one.  These 
are  contagious  diseases. 

3.  Transmission  is  chiefly  by  indirect  contact, 
or  through  food  or  water.  Direct  contact  plays  a 
role  in  some  instances,  and  rarely  the  air  may  be 
a  means  of  conveyance.  The  members  of  this 
group  are  not  highly  contagious  in  the  sense  of 
transmission  directly  from  one  individual  to  anoth- 


Facility       and 
Means    of 
Transmission. 


Personal 
Contact. 


Indirect 
Contact. 


20  IXFECTION    AND    IMMUNITY. 

er.  The  micro-organisms  are  excreted  mainly  by 
the  feces,  and  typhoid  and  paratyphoid  by  the 
urine.  As  a  rule  they  are  acquired  indirectly,  as 
through  a  water  supply  or  milk  which  have  been 
infected  from  discharges,  contamination  of  the 
hands  from  the  excreta  to  food.  Examples  are  ty- 
phoid, paratyphoid,  cholera  and  dysentery. 
Insects.  4.  Transmission  by  means  of  insects.  Some  of 
these  diseases,  as  malaria,  yellow  fever,  and  Eocky 
Mountain  spotted  fever,  are  not  contagious  at  all, 
but  are  nevertheless  communicable  through  the 
medium  of  the  proper  insect,  mosquitoes  or  ticks. 
South  African  tick  fever,  ordinary  relapsing  fever, 
plague  in  some  instances,  trypanosomiasis,  and 
probably  t3'phus  are  other  examples.  The  steps 
in  transmission  are  sometimes  very  complex,  and 
vary  a  great  deal*,  as  will  be  pointed  out  later. 

\ot  Trans-       5.  Trausmissiou    from   man   to   man    does   not 
missibie.   ^j^j.g  place  at  all  under  ordinary  conditions :  tet- 
anus, hydrophol)ia,  and  other  wound  infections. 

It  is  thus  seen  that  these  five  divisions  consti- 
tute a  series  in  which  contagiousness  finally  disap- 
pears.    The  subject  of  transmission  will  receive 
further  consideration  later. 
iiifectionN       It  has  been  stated  above  that  infectious  diseases 

sni>Ntnnee.«.  ^^^  causcd  by  living  pathogenic  organisms.  In- 
vestigations have  shown,  however,  that  the  toxic 
products  of  some  organisms  can  be  prepared  and 
separated  from  the  organisms  themselves  by  filtra- 
tion, and  that  such  microbe-free  toxins  when  in- 
jected into  animals  may  cause  the  same  symptoms 
that  are  produced  by  the  bacteria  themselves  (teta- 
nus and  diphtheria).  Accordingly,  for  the  sake  of 
convenience,  the^e  toxins  also  may  be  considered 
among  the  infectious   agents,  even   though   sepa- 


CLASSIFICATION   OF   ORGANISMS,  21 

rated  from  their  corresponding  bacteria.  The  va- 
rious infections  agents,  including  these  toxins,  find 
their  j)roper  places  in  the  following  classification, 
which,  for  the  most  part,  is  that  of  von  Behring: 

I.  Living  (i.  e..  pathogenic  parasites). 

A.  Macroparasites    (e.    g.,   intestinal   worms, 

pediculi  filarise,  uncinaria). 

B.  Microparasites. 

1.  Bacteria  (fission  fungi :  each  cell  di- 

vides into  two  in  proliferating) . 

2,  Fungi  of  more  complex  organization 

(e.  g.,  aspergillus,  oidia). 

3.  Protozoa    (e.  g.,  Plasmodium   mala- 

rice,  Amccha  coli). 

4.  Filterable,  ultramicroscopic  or  un- 
known micro-organisms. 

II.  Non-living  (i.  e.,  toxins) . 

A.  Animal  toxins  (e.  g.,  snake  venom). 

B.  Vegetable  toxins. 

1.  Non-bacterial  (e.  g.,  abrin.  from  the 

jequirity  bean;  ricin,  from  the  cas- 
tor oil  bean;  the  toxins  of  hay 
fever). 

2.  Bacterial. 

a.  Soluble  bacterial  toxins    (diph- 

theria and  tetanus) . 

b.  Intracellular  bacterial  toxins, 
which  are  not  secreted  by  the 
cells  in  a  soluble  form. 

In  the  subjects  to  be  considered  we  shall  deal 
chiefly  with  microparasites  and  the  diseases  which 
thev  cause. 


INFECTION    AND    IMMUNITY. 


Koch*H  La'v^'s. 


CHAPTER  11. 


INFECTIOUS   ETIOLOGY. 

It  is  evident  that  the  discoven-  of  the  specific 
organism  of  an  infectious  disease  is  of  the  great- 
est importance  for  purposes  of  serum  therapy,  vac- 
cination and  hygienic  prevention.  For  the  demon- 
stration of  a  virus,  it  is  not  in  all  cases  necessary, 
though  desirable,  that  the  organism  be  cultivated 
artificially,  nor  that  it  be  recognized  visually.  The 
conditions  in  rinderpest  may  be  cited  in  which  the 
body  fluids  of  a  diseased  animal,  known  to  contain 
the  infectious  agent,  are  used  for  immunization, 
although  the  microbe  itself  can  not  as  yet  be  culti- 
vated or  recognized. 

There  are  so  many  possibilities  of  error,  and  so 
many  errors  have  actually  been  made  in  regard  to 
infectious  etiology,  that  certain  requirements  in 
the  way  of  proof  are  now  habitually  demanded  be- 
fore a  particular  organism  can  be  accepted  as  the 
cause  of  a  disease.  These  requirements  are  most 
frequently  expressed  in  the  form  of  Koch's  laws, 
which  may  be  stated  as  follows  1.  The  suspected 
organism  must  be  found  constantly  in  the  proper 
tissues  of  an  animal  suffering  from  the  disease,  or 
which  has  died  from  it.  2.  The  organism  must  be 
cultivated  artificially  in  a  pure  state.  3.  It  must 
be  possible  to  reproduce  the  disease  in  a  suitable 
animal  by  inoculation  with  the  pure  culture.  4. 
The  organism  must  again  be  cultivated  in  a  pure 
state  from  the  tissues  of  the  experiment  animal. 


KOCH'S    LAWS.  23 

Since  these  laws  were  formulated  another  proce-  Assiutina- 

tion     Test. 

dure  has  been  evolved  which  may  give  valuable 
evidence  as  to  etiology.  This  pertains  to  the  ag- 
glutination test,  or,  as  we  speak  of  it  in  connection 
with  typhoid  fever,  the  Gruber-Widal  reaction. 
This  principle,  that  in  the  acquiring  of  immunity 
to  a  microbic  infection  the  serum  of  an  individual 
gains  in  agglutinating  power  for  the  micro-organ- 
ism, has  been  found  to  hold  true  in  many  infec- 
tions. Consequently,  if  one  has  in  hand  the  speci- 
fic micro-organism  for  a  disease,  he  would  expect 
the  serum  of  a  patient  sick  of  this  disease  to  have  a 
stronger  agglutinating  power  for  this  micro-or- 
ganism than  for  others  which  were  accidentally 
present ;  and  this  power  w^ould  also  be  greater  than 
that  possessed  by  the  serum  of  one  who  had  not 
had  this  particular  disease.  In  spite  of  some  pos- 
sibilities of  error  the  agglutination  test  has  been 
of  distinct  value  in  the  recognition  of  the  specific 
micro-organisms  in  certain  diseases,  as  in  the  case 
of  the  germ  of  epidemic  dysentery  (Shiga). 

Also  the  more  recent  development  of  the  opso- 
nins and,  particularly,  of  the  phenomenon  of  fixa- 
tion of  complement,  promise  to  be  of  value  in  the 
recognition  of  specific  micro-organisms. 

All  Koch's  laws  have  not  been  complied  w^ith  in  obstacles 
certain  cases,  because  of  various  difficulties  Laws.***^**'** 
w^hich  have  been  encountered.  First,  the  patho- 
genic protozoa  can  not  be  cultivated  on  artificial 
media  (we  must  except  the  success  of  'Noyj  and 
McISTeal  with  certain  tr3^panosomes,  and  of  Mus- 
grave  and  Clegg  with  the  Amceha  coli  under  sym- 
biotic conditions)  ;  second,  certain  bacteria  which 
may  be  found  constantly  in  a  given  disease  have 
not  been  cultivated  artificially  (spirillum  of  recur- 


24  INFECTWS^    AND    IMMUNITY. 

rent  fever)  ;  third,  there  are  a  few  diseases  which 
are  peculiar  to  man  and  accordingly  can  not  be  re- 
produced in  experiment  animals  (lepros}^,  scarlet 
fever,  measles,  etc.)  ;  fourth,  some  infectious  agents 
are  pathogenic  for  experiment  animals,  but  do  not 
reproduce  in  them  a  clinical  or  anatomic  condition 
identical  with  that  found  in  the  original  animal 
(typhoid). 

Furthermore,  failure  to  comply  with  all  the  re- 
quirements enumerated  does  not,  in  some  cases, 
disqualify  the  organism  as  the  causal  factor.  If 
an  organism  is  found  constantly  in  characteristic 
sites  in  a  given  disease  and  not  in  other  infections, 
and  if  at  the  same  time  other  microbes  are  not 
present  or  are  present  inconstantly  or  through  ac- 
cident, there  could  be  little  or  no  hesitation  in  ac- 
cepting this  organism  as  the  cause  of  the  disease, 
even  if  it  were  impossible  to  cultivate  it  or  to  trans- 
fer the  disease  to  animals.  The  typhoid  bacillus 
has  been  cultivated  from  characteristic  foci  (stools, 
blood,  spleen,  urine,  rose  spots)  in  such  a  large 
number  of  cases,  and  the  bactericidal  and  agglu- 
tinating powers  of  the  patient's  serum  against  this 
organism  are  so  distinctive,  that  compliance  with 
the  third  law,  though  desirable,  is  not  now  essen- 
tial. The  conditions  are  similar  in  reference  to 
cholera  and  the  cholera  vibrio. 

The  conditions  are  so  unique  in  some  diseases 
that,  although  all  Koch's  laws  have  not  been  met 
literally,  certain  equivalents  have  been  met.  To 
illustrate,  we  may  consider  an  anopheles  mosquito 
which  has  become  infected  with  the  plasmodium 
of  malaria  by  biting  a  malarial  patient,  as  a  cul- 
ture medium  ;  and  the  transferring  of  the  infection 


INFECTIOUS  DISEASES. 


25 


to  another  patient  by  the  bite  of  this  mosquito  as 
the  inoculation  experiment  which  is  desired. 

The  term  "specific  infectious  disease"  has  come  specific 

^  ■,.-,,  Infectious 

to  have  a  very  special  meaning.  It  is  applied  to  a  Diseases. 
disease  having  characteristic  clinical  and  anatomic 
phenomena,  which  can  be  caused  only  by  one  par- 
ticular micro-organism.  Among  the  diseases 
which  come  mthin  the  limits  of  this  brief  defini- 
tion, the  following  may  be  enumerated  (the  micro- 
organism which  is  the  cause  of  each  disease  being 
also  given),  for  the  sake  of  illustration. 


Diphtheria 

Tetanus 

Typhoid  fever 

Cholera 

Anthrax 

Tuberculosis 

Leprosy 

Plague 

Dysentery    (bacillary) 

Influenza 

Glanders   (farcy) 

Chancroid 

Eecurrent  fever 
Gonorrhea 

Epidemic  cerebrospi- 
nal meningitis 

Actinomycosis 

Blastomycosis 
Malaria 

Syphilis 


Bacillus  diplithericB 
Bacillus  tetani 
Bacillus  typhosus 
Vibrio  cholerce 
Bacillus  antliracis 
Bacillus  tuberculosis 
Bacillus  leprce 
Bacillus  pestis 
Bacillus  dysenterice 
Bacillus  influenzce 
Bacillus  mallei 
Bacillus    cliancri    mollis 

(Ducrey) 
Spirillum  ohermeieri 
Micrococcus  gonorrhoea 
Diplococcus   intracellula- 

ris     meningitidis     (of 

Weichselbaum) 
Actinomyces      bovis       et 

ho  minis 
Blastomycetes  and  Oiclia 
Plasmodium  malarice 
Spirochceta  pallida 


2G  INFECTION    AND    IMMUNITY. 

A  large  number  of  animal  diseases  have  their 
specific  microbes,  as  do  certain  other  human  dis- 
eases which  hardly  concern  us  as  to  the  subject  in 
hand. 
Unknown  lu  addition  to  the  diseases  mentioned,  there  are 
Etioiosy  ggveral,  of  unknown  etiology,  which  from  analogy 
we  must  recognize  as  entities  because  of  their  con- 
stant clinical  and  anatomical  manifestations.  Scar- 
let fever,  measles,  German  measles,  chickenpox, 
smallpox,  yellow  fever,  typhus  fever  and  hydro- 
phobia, are  undoubtedly  due  to  micro-organisms. 
Mallory  recently  found  in  the  skin  of  four  scar- 
let fever  patients  a  protozoon-like  body  which  he 
believes  to  be  the  cause  of  the  disease,  although 
he  admits  that  much  desired  proof  has  not  been  ob- 
tained. 

It  is  possible  that  smallpox  and  vaccinia  will  be 
eliminated  from  the  diseases  of  unknown  causa- 
tion, owing  to  the  evidence  of  protozoon  etiology 
that  Councilman  and  his  colaborers  have  obtained ; 
however,  for  the  present,  the  question  is  suh  judice 
in  view  of  the  fact  that  the  forms  described  bear  a 
close  resemblance  to  certain  well-known  types  of 
cell  degeneration. 

The  following  animal  diseases,  of  unknown 
etiology,  may  also  be  mentioned  in  this  connec- 
tion :  Foot  and  mouth  disease,  peripneumonia, 
bovine  pest,  sheep-pox  (clavelee),  chicken-typhus 
or  chicken-pest  and  epithelioma  contagiosum  of 
fowls. 
obstacieH  to  Thc  following  appear  to  be  the  chief  reasons  for 
^'"aiicpobe*!*'  the  failure  to  discover  the  organisms  of  these  dis- 
eases:  1.  Inability  to  cultivate  the  microbe.  2. 
Mixed,  or  symbiotic  infections.  For  a  long  time  it 
was  supposed  tbat  the  so-called  hog-cholera  bacillus 


SPECIFICITY    OF   ORGANISMS.  27 

is  the  cause  of  hog  cholera.  Eecent  experiments, 
however,  have  disclosed  that  the  true  virus  is  ultra- 
microscopic  and  filterable,  the  bacillus  being  only 
a  more  or  less  constant  associate.  It  is  conceivable 
that  in  some  cases  the  combined  action  of  two 
micro-organisms  may  be  necessary  to  cause  the 
disease.  The  non-toxic  products  of  the  two  may 
synthesize  to  form  a  toxic  substance  (Hektoen.)  3. 
Unstainability  of  the  microbe.  4.  Ultramicro- 
scopic  size.  The  organism  of  the  peripneumonia  of 
cattle  was  cultivated  by  Nocard  and  Eoux  by  grow- 
ing it  in  a  closed  collodion  sac  which  was  placed  in 
the  peritoneal  cavity  of  suitable  animals.  It  is  so 
small  that  its  form  can  not  be  made  out,  and 
growth  is  recognized  only  by  clouding  of  the 
culture  medium,  and  the  increased  virulence  of  the 
latter  for  animals. 

Some  valuable  information  has  been  obtained  Fiiterabiiity 
by  observing  w^hether  the  infectious  agents  are  ^  ^  ^^  • 
so  small  that  they  Avill  pass  through  dense  filters 
of  porcelain  or  infusorial  earth.  It  has  been  found 
that  the  viruses  of  foot  and  mouth  disease,  peri- 
pneumonia, rinderpest,  sheep-pox,  chicken-typhus, 
horse  sickness,  epithelioma  contagiosum  of  fowls, 
yellow  fever,  hydrophobia,  and  hog  cholera  are  fil- 
terable. This  is  determined  by  injecting  the  fil- 
tered culture  medium  or  serum  into  susceptible 
animals.  The  viruses  of  smallpox,  vaccinia,  and 
Eocky  Mountain  spotted  fever  are  not  filterable. 
Inasmuch  as  scarlet  fever,  measles,  chicken-pox 
and  typhus  fever  cannot  be  produced  in  animals, 
the  fiiterabiiity  of  their  viruses  is  not  at  present 
susceptible  to  determination. 

There  is  a  marked  tendency  in  many  diseases, 
typhoid,  cholera,  malaria,  etc.,  for  characteristic 


28  INFECTION    AND    IMMUNITY. 

organs  or  groups  of  organs  to  be  involved  in  some 
particular  manner.  These  are  features  which, 
together  with  a  constant  bacteriology,  stamp  them 
as  specific  diseases.  On  the  other  hand,  a  large 
number  of  micro-organisms  cause  no  well-defined 
clinical  and  anatomic  disease,  but,  depending  on 
various  accidents,  cause  an  inflammation  now  in 
one  organ,  now  in  another. 

Eegarding  the  production  of  suppuration,  the 
pyogenic  poorer  is  common  to  a  large  num])er 
of  microbes.  A  diphtheritic  or  pseudo-diphtheri- 
tic process  in  the  mouth  and  throat  may  be  caused 
by  the  diphtheria  bacillus,  streptococcus,  staphylo- 
coccus, oidium  or  yeasts;  bronchitis  may  be  caused 
by  the  influenza,  tubercle,  plague  and  typhoid 
bacilli,  and  by  the  infecting  agents  of  the  acute 
exanthemata,  etc.;  pulmonitis  by  the  pneumococ- 
cus,  streptococcus,  tubercle,  plague,  Friedlander 
and  influenza  bacilli,  oidium,  actinomyces,  etc. ; 
meningitis  by  the  tubercle  and  influenza  bacilli, 
streptococcus,  staphylococcus,  pneumococcus,  gono- 
coccus,  diplococcus  of  epidemic  meningitis,  the 
syphilis  virus,  etc. ;  arthritis  by  the  streptococcus, 
staphylococcus,  tubercle  bacillus,  gonococcus,  the 
virus  of  rheumatic  fever,  etc.;  endocarditis  by  the 
streptococcus,  staphylococcus,  gonococcus,  pneu- 
mococcus, tubercle  bacillus,  etc.,  and  septicemia 
by  a  whole  host  of  organisms  aside  from  those 
mentioned  as  causing  specific  diseases. 

Within  certain  limits,  however,  there  is  often  a 
degree  of  specificity  in  the  processes  produced  by 
some  of  the  organisms  mentioned,  which  some- 
times allows  of  clinical  and  anatomic  differentia- 
tion.    The  infiltrating  and  rapidly  extending  in- 


SYMBIOSIS.  29 

t 

vasion  of  the  subcutaneous  and  connective  tissues 
caused  by  the  streptococcus  can  often  be  distin- 
guished clinically  from  the  slower,  more  circum- 
scribed process  caused  by  the  staphylococcus.  The 
conditions  induced  by  the  Bacillus  aerogenes  cap- 
sulatus,  the  bacillus  of  malignant  edema,  are,  in 
turn,  different  from  those  of  the  streptococcus  and 
staphylococcus.  The  pneumococcus  commonly 
causes  the  consolidation  of  rather  extensive  areas 
of  the  lung,  whereas  the  streptococcus  and  the 
bacillus  of  Friedlander  are  more  often  found  in 
the  lobular  consolidations.  The  membranous  in- 
flammation of  diphtheria  may  in  favorable  cases 
be  distinguished  from  that  of  the  pyogenic  organ- 
isms without  bacteriologic  aids ;  in  this  possibility, 
however,  there  lies  no  justification  for  neglect  of 
the  bacteriologic  examination. 

In  nature  pathogenic  micro-organism- s  are  often  symbiosis. 
found  side  by  side  with  saprophytes  or  with  other 
pathogenic  bacteria,  and  at  times  their  viability  is 
profoundly  influenced  by  their  associates.  Thus 
it  is  found  that  the  bacilli  of  plague  and  typhoid 
and  the  vibrio  of  cholera  do  not  live  long  in  the 
presence  of  many  saprophytic  organisms.  In  some 
instances  this  may  be  due  to  the  exhaustion  of  the 
nutrient  material  by  the  more  rapidly  growing 
saprophytes,  whereas  in  others  it  may  be  referable 
to  an  antagonistic  action  of  one  organism  on  the 
other.  On  the  other  hand,  the  relationship  may  be 
a  favorable  one.  The  existence  of  anaerobic  or- 
ganisms in  nature,  such  as  the  tetanus  bacillus  or 
the  bacillus  of  malignant  edema,  may  be  favored 
by  a  luxuriant  growth  of  aerobic  organisms  in 
their  immediate  vicinitv. 


30  INFECTION    AND    IMMUNITY. 

This  relationship  is  investigated  experimentally 
either  by  growing  two  organisms  in  mixed  cul- 
tures, noting  subsequently  whether  one  has  out- 
grown the  other,  or  one  may  be  grown  on  a  me- 
dium which  has  previously  been  utilized  by  the 
other.  The  predominance  of  one  or  the  other  may 
depend  on  the  nature  of  the  culture  medium.  This 
principle  is  utilized  in  obtaining  pure  cultures  of 
the  cholera  vibrio  from  dejecta  by  the  use  of  a 
strong  alkaline  medium  which  favors  the  growth 
of  the  cholera  vibrio  but  inhibits  that  of  the  other 
intestinal  bacteria.  Similarly  the  diphtheria  bacil- 
lus grows  well  on  Loeffler's  blood  serum,  whereas 
the  other  organisms  commonly  found  in  the  tliroat 
do  not. 

Garre  distinguished  a  one-sided  and  a  mutual 
antagonism  between  bacteria,  but  the  former  seems 
to  be  the  more  common.  Examples  of  favorable 
symbiosis  on  suitable  culture  media  are  the  fol- 
lowing :  Streptococcus  and  cholera  vibrio ;  anthrax 
and  pyocyaneus  bacilli  (Turro) ;  diphtheria  bacil- 
lus and  the  streptococcus  (Hilbert).  In  plate  cul- 
tures it  has  been  found  that  the  influenza  bacillus 
produces  unusually  large  colonies  when  they  lie 
adjacent  to  colonies  of  the  staphylococcus  (Grass- 
Ijerger),  and  that  it  grows  vigorously  on  agar 
which  contains  killed  bodies  of  the  gonococcus  or 
diphtheria  bacillus  (Cantani).  It  has  been  noted 
tjiat  the  diphtheria  bacillus  is  stimulated  to  a 
greater  production  of  toxin  by  the  presence  of 
streptococci. 
>ii.x*Mi  The  coexistence  of  two  or  more  micro-organisms 
in  a  morbid  condition  is  of  frequent  occurrence, 
and  some  of  the  most  interesting  and  important 


InfectiniiM 


MIXED    INFECTIONS.  31 

phenomena  of  infectious  diseases  are  referable  to 
mixed,  secondary  or  superimposed  infections. 

Two  exogenous  infections  may  attack  an  indi- 
vidual at  the  same  time.  Measles  and  scarlet  fever 
and  diphtheria  and  scarlet  fever  have  been  known 
to  coexist.  Pneumococcus  pneumonia  and  typhoid 
fever,  chancre  and  soft  chancre  with  pus  cocci, 
syphilis  and  gonorrhea,  diphtheria  with  strepto- 
cocci, tetanus  with  gangrene-producing  organisms, 
are  common  observations.  One  organism  may  in- 
tensify the  virulence  of  another.  Diphtheria  ac- 
companied by  streptococcus  infection  seems  to  be 
more  virulent  than  diphtheria  alone.  It  is  also 
believed  that  the  presence  of  aerobic  organisms 
(those  which  demand  oxygen  for  their  develop- 
ment) in  a  wound  infected  with  the  tetanus  bacil- 
lus or  the  bacillus  of  malignant  edema  (anaerobic 
organisms),  may  increase  the  virulence  of  these 
infections.  Streptococci  are  probably  important 
organisms  in  scarlet  fever,  for  they  are  present  in 
unusual  numbers  in  the  throat  lesions  and  are 
often  found  in  fatal  cases  in  all  the  organs,  yet  it 
is  possible  that  they  inaugurate  only  a  mixed  or 
secondary  infection  superimposed  on  that  of  the 
scarlatina  virus.  The  conditions  are  somewhat 
similar  in  smallpox,  the  pustules  of  which  invari- 
ably contain  streptococci,  staphylococci,  or  both. 
In  both  scarlatina  and  smallpox  these  secondary 
infections  may  be  responsible  for  many  fatalities. 

Pneumococcus  pneumonia  occurring  during  the 
course  of,  or  during  convalescence  from  the  erup- 
tive fevers,  diphtheria,  typhoid  fever  or  erysipelas ; 
a  streptococcus  septicemia  developing  during 
typhoid   (giving  rise  to  an  irregular  temperature 


32  INFECTION    AND    IMMUNITY. 

curve),  streptococcus  infection  of  tubercular  cavi- 
ties, and  the  development  of  acute  tuberculosis 
during  measles — these  are  important  examples  of 
secondary  infections. 

We  should  naturally  expect  that  the  presence  of 
a  severe  secondary  infection  might  embarrass  at- 
tempts at  serum  therapy  and  vaccinal  therapy. 
Experience  regarding  the  former  is  limited  prac- 
tically to  diphtheria,  and  there  is  no  lack  of  evi- 
dence to  show  that  the  disease  when  complicated 
by  severe  streptococcus  infection  sometimes  can- 
not be  controlled  by  antitoxin  treatment;  and  in 
vaccinal  therapy  (injection  of  micro-organisms  or 
their  products)  it  is  emphasized  from  all  sides  that 
in  the  presence  of  mixed  infection  it  is  advisable 
to  inject  preparations  of  the  secondary  as  well  as 
the  primary  organisms  concerned. 


CHAPTER  III. 


INFECTION   ATRIA  AND  THE   EXCRETION   OF  MICRO- 
ORGANISMS. 

Infection  Atria. 

The  infection  atrium  is  the  primary  point  of 
invasion  by  micro-organisms,  or  the  point  or  tissue 
or  surface  through  which  they  reach  internal 
structures. 

In  general,  mJcro-organisms  may  enter  the  body 
through  any  of  its  surfaces,  except,  of  course,  the 
serous  coverings.  Anatomical  structure,  however, 
renders  the  skin,  and  other  surfaces  which  are 
clothed  with  pavement  epithelium,  quite  resistant 
to  penetration,  in  the  absence  of  wounds.  Leav- 
ing wound  infection  out  of  consideration  the  mu- 
cous surfaces  afford  the  most  frequent  points  of 
entrance. 

Certain  micro-organisms  appear  to  have  a  pred^-  preferred  or 
lection  for  particular  tissues,  preferring  one  point  ^riiu*^ 
of  entrance  or  primary  involvement  above  all 
others.  Thus,  in  so  far  as  we  know,  the  typhoid 
bacillus  and  the  cholera  vibrio  always  produce 
their  primary  infection  in  the  intestines,  although 
a  hematogenous  typhoid  is  sometimes  spoken  of, 
the  true  atrium  escaping  detection.  The  diph- 
theria bacillus  habitually  makes  its  attack  in  the 
upper  respirator}^  passages.  It  is  probable  that 
measles  and  scarlet  fever  utilize  the  respiratory 
tract  for  the  point  of  invasion,  although  this  can- 
not be  determined  positively  at  present.  As  will 
be  described  later,  many  microbes  have  a  predilec- 


34  INFECTION    AND    IMMUNITY. 

tion  for  certain  tissues  after  they  reach  the  interior 
of  the  body. 

Sometimes  it  would  appear  that  a  particular 
surface  is  joredilected  only  because  it  is  the  area 
which  is  most  commonly  exposed  to  infection. 
Thus,  syphilis  is  usually  a  venereal  disease,  al- 
though on  proper  exposure  chancres  occur  readily 
on  the  lip,  the  mucous  membranes  of  the  mouth, 
•  tonsils,  or  through  wounds  in  the  skin.     Hence 

the  predilection  of  the  primary  sore  for  the  geni- 
tals is  only  apparent.  Also  the  diphtheria  bacillus 
occa.sionall}^  is  inoculated  into  wounds  on  cutane- 
ous surfaces  and  in  the  vagina.  Some  mucous 
surfaces  are  protected  against  microbic  invasion 
by  the  character  of  their  secretions,  as  in  the  cases 
of  the  stomach  and  vagina  (See  under  ^^Xatural 
Immunity"). 
cryptoj^eii-  lu  the  so-callcd  cryptogenetic  infections  the 
****'  Vioiis'  atrium  escapes  detection.  Certain  micro-organisms 
may  enter  the  body  without  causing  a  discoverable 
reaction  at  the  point  of  entrance  (plague).  Ex- 
perimentally it  lias  been  shown  that  tubercle  ba- 
cilli readily  pass  through  the  intestinal  wall  into 
the  mesent«ric  lympli  glands  without  causing  le- 
sions of  the  intestines.  Leucocytes  may  carry  or- 
ganisms through  the  intact  surface  of  the  intes- 
tines into  the  deeper  tissues,  and  possil)ly  the  same 
process  occurs  in  the  lungs,  particularly  in  rela- 
tion to  tlie  tubercle  bacillus  ( !). 
Skin.  Infection  through  the  skin  commonly  take? 
place  through  wounds  (tetanus,  glanders,  malig- 
nant edema  and  purulent  infections),  although  the 
wound  may  be  so  small  as  not  to  be  discoverable 
(bubonic  plague).  "Insect-borne"  diseases  are 
inoculated   through   the   skin   by   the  bites  of  the 


INFECTION   ATRIA. 


35 


insects.  In  the  case  of  pJagne  the  bacilli  may  be 
deposited  on  the  skin  in  the  feces  of  the  flea  and 
subsequently  inoculated  by  means  of  rubbing  or 
scratching.  The  guinea-pig  may  be  infected  with 
plague  by  rubbing  a  culture  on  the  shaven  skin. 
Minute  wounds*  probably  exist.  Staphylococci  may 
reach  the  hair  follicles  as  a  consequence  of  rub- 
bing and  cause  f urunculosis  after  penetrating  the  , 
soft  epithelium  of  the  follicle. 

The  conjunctiva  has  rather  high  resistance  for  Eye 
some  micro-organisms^  as  the  anthrax  bacillus, 
and  it  harbors  staphylococci  continuously.  It  may 
be  invaded,  however,  by  the  gonococcus  (especially 
in  children),  pneumococcus,  streptococcus,  staphy- 
lococcus, diphtheria  bacillus,  Morax-Axenfeld  ba- 
cillus, and  probably  the  meningococcus.  The 
plague  bacillus  will  cause  generalized  infection 
through  the  conjunctiva  in  rats,  and  it  is  reported 
that  glanders  and  hydrophobia  (Conte,  Galtier) 
may  also  gain  entrance  through  the  conjunctiva. 

The  nasal  passages  become  infected  with  the 
organisms  causing  coryza,  with  the  organisms  of 
diphtheria,  influenza,  glanders,  leprosy  and  with 
the  pyogenic  cocci.  Some  of  these  may  extend  to 
the  adjacent  cavities,  antrum  of  Highmore,  frontal 
ginuses,  and  the  middle  ear  through  the  Eustachian 
tube.  On  account  of  the  proximity  of  the  nasal 
passages  to  the  brain,  and  the  lymphatic  communi- 
cations, it  is  probable  that  meningitis  (pneumo- 
coccic  and  epidemic  cerebrospinal)  often  arises  by 
extension  of  the  organisms  from  the  nose  to  the 
meninges  through  the  ethmoid. 

Actinomycosis,  syphilis,  occasionally  tuberculo- 
sis (tongue),  noma,  thrush,  and  in  children  gon- 
orrhea may  find  primary  location  in  the  mouth. 


Nasal 
Cavities, 


3IOQth. 


36 


INFECTION    AND    IMMUNITY. 


Tonsils. 


Lnn^s. 


Stomacli 
Intestines      ^^^^'* 


'  Streptococci,  pneumococci  and  diphtheria  read- 
ih'  attack  the  tonsils,  and  it  is  probable  that  the 
tubercle  bacillus  often  enters  through  them,  with 
or  without  causing  local  infection.  Similarly  it  is 
believed  b}^  many  that  organisms  causing. septice- 
mia (particularly  the  streptococcus),  acute  articu- 
lar rheumatism,  and  osteomyelitis  may  enter 
through  the  tonsils,  and  this  may  also  be  the  case 
in  scarlet  fever. 

The  bronchi  become  infected  by  the  various  or- 
ganisms causing  bronchitis  (streptococcus,  pneu- 
mococcus,  influenza  bacillus,  etc.),  and,  either 
through  surface  or  lymphatic  extension,  or  by  deep 
inspiration,  these  and  many  other  organisms,  as 
the  tubercle  and  plague  bacilli,  and  the  actino- 
myces,  reach  the  deeper  recesses.  Some  of  the  ex- 
anthemata, as  measles  and  smallpox,  may  find  en- 
trance through  the  pulmonary  tissue.  As  explained 
later,  '^dust  infection"  and  ^^droplet  infection"  are 
of  great  importance  in  pulmonary  involvement, 
particularly  in  relation  to  tuberculosis.  "Pri- 
mary" tuberculosis  of  the  peribronchial  lymph 
glands  indicates  that  some  micro-organisms  may 
traverse  the  bronchi  without  involving  them. 

The  stomach  is  comparatively  free  from  infec- 
The  intestines  provide  an  atrium  for  ty- 
phoid, cholera,  dysentery  (bacillary  and  amebic), 
tuberculosis,  plague,  anthrax,  in  children  for  the 
streptococcus,  Bacillus  pyocyaneus  and  others;  in 
animals,  for  anthrax,  plague,  swine  plague,  mouse 
typhus,  chicken  cholera,  hemorrhagic  septicemias, 
intestinal  diphtheria  of  rabbits,  and  others. 

The  extent  to  which  micro-organisms  are  carried 
from  the  intestines  into  the  body  in  a  state  of 
health  is  greatly  disputed,  but  frequent  existence 


Tract. 


INFEGTIVITY    OF    EXCRETIONS,  37 

of  primary  tuberculosis  of  the  mesenteric  lymph 
glands  indicates  that  it  probably  occurs. 

Rectum. — Gonorrhea,  septic  infection  of  hemor-  Rectum  and 

,      .  T    ,         .  ;>       r  Genito- 

rhoidal  veins.  urinary 

TJretlira. — Gonorrhea,    syphilis;    "simple"    ure- 
thritis due  to  other  causes. 

Bladder  and  Ureters. — Infection  usually  second- 
ary, by  extension  or  from  the  blood  stream. 

External  Genitals. — Hard  and  soft  chancres. 
Diphtheria  in  girls. 

Female  Genital  Tract. — Gonorrhea,  especially  in 
the  cervix,  which  is  covered  by  soft  cuboidal  epithe- 
lium. The  vagina  is  quite  resistant  owing  to  its 
covering  of  pavement  epithelium  and  the  bacteri- 
cidal character  of  its  secretion.  Virulent  pyogenic 
organisms  sometimes  are  found  in  the  nonnal 
vagina  and  they  may  occasionally  be  responsible 
for  puerperal  infections. 

The  above  refers  to  primary  invasion.  It  is  well 
known  that  many  of  these  surfaces  and  the  organs 
which  they  cover  are  frequently  involved  subse- 
quent to  initial  infection  at  some  other  point.  This 
is  secondary,  or,  better,  metastatic  infection. 

Excretion  of  Micro-organisms. 
In  the  transmission  of  an  infection  from  person 
to  person,  without  the  intervention  of  an  inter- 
mediate host  (insects),  the  process  naturally  pre- 
supposes that  the  micro-organisms  are  excreted  or 
discharged  from  the  body  of  the  patient  through 
one  channel  or  another.  Eegarding  the  likelihood 
of  transmission,  in  the  event  of  excretion,  this 
will  depend  on  the  character  of  the  organism,  its 
viability  under  the  conditions  of  excretion,  the  in- 
fection atrium  which  it  demands,  and  whether  or 


38 


INFECTION    AND    IMMUNITY. 


Relation    of 

Excretion  to 

Site    of 

Involvement. 


Metastatic 
Infections. 


not  it  is  discharged  in  such  manner  that  it  is  read- 
ily disseminated.  Some  of  these  points  are  con- 
sidered in  following  chapters. 

As  a  general  principle  it  may  be  stated  that 
when  the  surfaces  of  the  body  are  the  seat  of  infec- 
tion the  micro-organisms  are  discharged  into  the 
outer  world  more  or  less  easily.  This  applies  not 
only  to  the  cutaneous  surface,  but  also  to  the  mu- 
cous surfaces,  as  the  lungs,  alimentary  tract,  gall- 
bladder, and  urinary  bladder,  and  also  to  discharg- 
ing sinuses  and  abscesses  which  rupture  through  a 
cutaneous  or  mucous  surface.  The  surfaces  mat 
be  involved  either  primarily,  as  in  tuberculosis  or 
blastomycosis  of  the  skin,  or  as  a  part  of  a  gener- 
alized infection,  as  in  the  case  of  some  of  the 
eruptive  diseases.  Thus  from  the  respiratory  pas- 
sages the  microbes  of  pneumonia,  tuberculosis, 
diphtheria,  tonsillitis  caused  by  other  micro-organ- 
isms, plague  pneumonia,  influenza,  whooping- 
cough,  epidemic  cerebrospinal  meningitis  and 
probably  measles,  scarlet  fever  and  smallpox,  are 
discharged  into  the  surrounding  air.  From  the 
intestinal  tract  the  micro-organisms  of  tubercu- 
losis, typhoid  fever,  cholera  and  of  other  less  im- 
portant diseases  reach  the  outer  world.  From  the 
geni to-urinary  tract,  those  of  gonorrhea,  syphilis, 
tuberculosis,  typhoid  and  paratyphoid  fevers ;  'from 
the  skin  the  microbes  of  ulcerative  processes,  the 
contagious  dermatoses,  trichophytosis,  favus,  etc., 
and  probably  some  of  the  contagions  exanthemata 
(scarlet  fever,  measles,  etc.). 

Of  great  importance  is  the  fact  that  some  infec- 
tions which  are  primarily  systemic,  or  become  so 
during  the  course  of  infection,  commonly  involve 
some  excreting  organ  secondarily,  thus  rendering 


INFECTION    CARRIERS.  39 

possible^  or  increasing,  tlie  discliarge  of  the  organ- 
isms. In  a  large  percentage  of  the  cases  of  typhoid 
fever  the  kidneys  become  the  seat  of  numerous 
foci  of  metastatic  infection,  resulting  in  the  elim- 
ination of  large  quantities  of  living,  virulent  ty- 
phoid bacilli  in  the  urine.  A  similar  event  happens 
in  parat3^phoid  fever,  and  in  systemic  tuberculosis, 
and  Koch  has  even  suggested  that  sleeping  sickness 
may  be  acquired  by  coitus.  "Milk  sickness,"  which 
apparently  is  acquired  through  the  gastro-intes- 
tinal  tract,  is  transmitted  through  the  milk  (Jor- 
dan and  Harris),  and  the  same  is  true  of  Malta 
fever.  The  virus  of  hydrophobia  is  excreted 
through  the  salivary  glands.  Experimentalh', 
pneumococci  and  anthrax  bacilli,  when  injected 
into  the  circulation,  have  been  recovered  from  the 
intestinal  tract.  This  was  also  done  with  the 
vibrio  of  cholera  in  guinea-pigs  (Kolle  and 
Issaeff). 

These  statements  are  made  with  reference  to  "Carriers." 
the  discharge  of  micro-organisms  during  actual 
disease.  Investigations  have  shown,  however,  that 
infections  on  a  large  scale,  reaching  even  epidemic 
proportions,  are  frequently  derived  from  those  who 
apparently  are  in  a  state  of  good  health.  Usually, 
but  not  always,  this  concerns  individuals  who  have 
suffered  from  the  infection  at  some  previous  time. 
and  they  are  known  as  "bacillus  carriers,"  or  sim- 
ply "carriers." 

The  vibrio  of  cholera  may  be  excreted  in  the 
stools  for  forty-eight  days  after  the  recovery  of 
the  patient  (Kolle).  Virulent  diphtheria  bacilli 
may  be  discharged  from  the  mouth  and  nose  for 
months  after  recovery  from  the  disease^,  and  in  the 
case  of  rhinitis  fihrinosa  chronica  this  may  persist 


40  INFECTION    AND    IMMUNITY. 

for  years.  "Latent"  gonorrhea  is  frequently  in- 
fective. The  urine  after  recovery  from  typhoid 
fever  may  contain  the  bacilli  for  months  (Pe- 
truschky  and  others),  and  the  recent  study  of  ty- 
phoid carriers  has  shown  that  they  may  discharge 
bacilli  in  the  stools  for  many  years  (twenty  or 
more).  In  some  instances  it  has  been  supposed 
that  the  gall-bladder  is  in  a  state  of  chronic  in- 
fection with  the  bacilli  and  serves  as  a  reservoir 
for  continuous  flooding  of  the  intestines.  The 
value  of  the  remedial  measure  suggested — i.  e..,  the 
extirpation  of  the  gall-bladdei' — has  not  yet  been 
demonstrated.  AYe  cannot  leave  out  of  mind  the 
possibilit}''  that  the  typhoid  bacillus,  in  some  in- 
stances, may  become  habituated  to  the  intestinal 
environment  and  multiply  there;  in  such  cases  it 
would  not  be  necessary  to  assume  another  source 
of  replenishment.  The  dissemination  of  micro- 
organisms by  insects  which  have  fed  on  infected 
blood  is  apart  from  excretion  and  is  considered 
under  the  subject  of  "Insect  Transmission"  Chap- 
ter VI.). 


CHAPTEE  IV. 


SOURCES  OF  PATHOGENIC  MICRO-ORGANISMS. 

(1)  Earth,  Etc.;  (2)  Food  Substances;  (3)  Ani- 
mals; (Jf)  Body  Surfaces  of  the  Individual. 

Micro-organisms  which  produce  disease  in  man 
may  be  derived  (1)  from  the  earth,  other  inani- 
mate material,  or  from  vegetable  growth;  (2) 
from  water,  milk  or  other  food  substances;  (3) 
from  animals,  directly  or  indirectly;  (4)  from  the 
body  surfaces  of  the  individual  himself;  (5)  from 
other  human  beings,  and  (6)  from  insects. 

1.  The  extent  to  which  the  superficial  earth  is  Eartn. 
contaminated  with  micro-organisms  depends  on 
various  conditions,  particularly  the  presence  of 
dead  organic  matter,  moisture,  temperature,  the 
degree  of  exposure  to  light  and  sunlight,  the  chem- 
ical composition  of  the  soil,  and  the  admixture  of 
animal  excretions.  Some  of  them  inhabit  the  soil 
naturally  and  are  comparatively  harmless  sapro- 
phytes, and  may  even  be  of  great  value  in  the 
regeneration  of  soils.  Others,  of  pathogenic  char- 
acter, seem  to  occur  naturally  in  the  earth  or  on 
vegetation,  where  they  multiply  readily  (the  pyo- 
genic cocci,  actinomyces).  On  the  other  hand,  a 
large  number  of  pathogenic  organisms  reach  inan- 
imate nature  only  as  they  are  deposited  with  the 
excretions  of  man  (those  of  typhoid,  paratyphoid, 
dysenter}^,  cholera,  plague,  tuberculosis,  etc.),  or  of 
animals  (tetanus  bacilli).  Many,  as  the  organisms 
of  typhoid,  cholera  and  plague,  probably  do  not 
proliferate  at  all  in  the  earth,  although  some  (tet- 


42  INFECTION    AND    IMMUNITY. 

anus  bacillus  and  that  of  malignant  edema)  re- 
tain life  and  virulence  for  a  long  time.  It  is  still 
uncertain  whether  the  latter  proliferate  in  this  sit- 
uation, or  whether  they  persist  merely  through  the 
agency  of  their  resistant  spores.  Inasmuch  as  they 
are  anaerobic  in  character,  their  life  may  in  some 
instances  be  prolonged  through  symbiotic  aerobic 
organisms,  which  surround  them  and  create  for 
them  an  atmosphere  which  is  poor  in  oxygen.  The 
presence  of  many  saprophytes  is  unfavorable  to 
the  life  of  certain  micro-organisms  in  the  soil  (t}^- 
phoid,  plague).  In  so  far  as  is  known  none  of 
the  protozoa  which  are  pathogenic  for  man  occur 
in  the  soil  naturally. 
Water,  and  S-  Water,  milk  and  other  food  substances  rarely 
Substances!  harbor  important  pathogenic  organisms  under  nat- 
ural conditions.  On  the  other  hand,  they  play  a 
very  important  part  in  carrying  such  microbes 
from  man  to  man,  and  in  some  instances  from 
animals  to  man,  as  explained  in  succeeding  chap- 
ters. Stagnant  water  frequently  sets  up  acute  enter- 
itis, which  may  in  some  instances  be  due  to  its 
chemical  constituents  and  in  others  to  saprophytic 
organisms. 

Solid  foods,  as  fruits  and  vegetables,  may  occa- 
sionally harbor  bacteria,  particularly  when  in  a 
state  of  deca}',  which  have  moderate  pathogenic 
powers  for  the  intestinal  tract;  or,  by  providing 
suitable  alimentation  or  otherwise  modifying  the 
contents  or  resistance  of  the  alimentary  tract,  mav 
render  organisms  virulent  which  otherwise  would 
be  harmless. 

Meats,  healthy  in  tlie  first  instance,  are  subject 
to  invasions  by  micro-organisms  from  the  intes- 
tinal tract,  after  the  death  of  the  animals  (fowls, 


INFJ^CTION   FROM    MILK. 


43 


fish,  oysters),  or  they  may  be  contaminated  by 
unclean  and  improper  preservation  later.  The 
symptoms  caused  by  their  ingestion  are  actual  in- 
fections in  some  instances  (as  with  Bacillus  enter- 
itidis),  whereas  in  others  the  condition  may  be  one 
of  intoxication  by  the  products  of  saprophytic  ac- 
tivity (Bacillus  hotulinus). 

Some  vegetables  contain  highly  poisonous  alka- 
loids and  toxins,  which  rarely  find  a  place  in  dis- 
ease. Some  of  them  have  been  of  great  value  in 
the  experimental  study  of  toxins  and  antitoxins. 
(See  table  at  close  of  Chapter  I.) 

3.  Animals  are  sometimes  subject  to  infection  Animals. 
by  microbes  which  are  also  pathogenic  for  man, 
transmission  taking  place  through  the  consump- 
tion of  diseased  meat  or  milk,  or  through  direct 
or  indirect  contact,  through  wounds,  or  by  the 
bites  of  insects. 

In  bovine  tuberculosis  the  udder  is  frequently  miiic. 
involved,  and  in  such  cases  large  quantities  of  the 
bacilli  are  excreted  by  the  milk.  Although  the 
virulence  of  the  bovine  bacillus  for  man  may  not 
be  so  great  as  that  of  human  tuberculosis,  it  is 
now  well  established  that  it  often  infects  man, 
perhaps  children  more  frequently  than  adults.  The 
cow's  udder  is  occasionally  involved  in  infections 
with  streptococci,  which,  being  excreted  in  the 
milk,  are  capable  of  causing  severe  enteritis  when 
the  milk  is  ingested. 

The  micro-organism  of  milk  sickness  is  trans- 
ferred in  a  similar  wa}^,  and  only  recently  it  has 
been  shown  clearly  that  man  (in  Malta)  becomes 
infected  with  Malta  fever  by  the  consumption  of 
the  milk  of  goats.    A  very  large  percentage  of  these 


44  INFECTION    AXD    IMMUNITY. 

animals  was  found  suffering  from  the  disease,  and, 
since  the  use  of  goat's  milk  has  been  prohibited, 
the  incidence  of  the  disease  in  man  has  undergone 
an  astonishing  decrease.  It  seems  to  have  been 
demonstrated  that  both  horses  and  cattle  occa- 
sionally suffer  from  generalized  infections  with  the 
paratyphoid  bacillus,  and  with  Bacillus  enteritidis. 
and  epidemic  infections  with  the  former  have  been 
traced  to  the  consumption  of  diseased  meats.  Bot- 
ulism and  trichiniasis  are  derived  in  the  same 
wa3\  In  some  instances  infection  of  the  meat 
probably  takes  place  during  or  subsequent  to 
slaughtering. 
By  Contact.  Authrax,  glanders  and  actinom3'Cosis  are  con- 
veyed to  man  from  animals  by  contact,  the  first 
two  being  contagious ;  and  hydrophobia  by  the  bites 
of  rabid  animals — i.  e.,  by  wound  infection. 
By  Insects.  In  a  few  instances  infections  are  transmitted 
from  an  animal  to  man  by  means  of  insects.  Thus, 
the  conveyance  of  plague  from  the  rat  by  the  flea 
is  one  of  the  means  by  which  man  contracts  this 
disease.  The  tsetse  fly  of  South  Africa,  which 
inoculates  man  with  the  trypanosome  of  sleeping 
sickness,  seems  to  derive  its  infection  from  wild 
animals  in  some  instances,  although  human  pa- 
tients are  also  an  important  source  of  infection  for 
fresh  flies.  The  virus  of  Rocky  Mountain  spotted 
fever  probably  passes  at  least  a  part  of  its  exist- 
ence in  the  body  of  one  or  more  species  of  small 
wild  animals,  and  this  step  seems  necessary 
for  the  maintenance  of  virulence.  In  connection 
with  malaria,  relapsing  fever,  South  African  tick 
fever  and  the  piroplasmoses  a  third  host  seems  to 
play  no  role,  or,  at  any  rate,  not  a  necessary  role. 


Infection." 


AUTOINFECTION.  45 

Snake  venoms,  and  the  poisons  of  spiders,  bees, 
and  various  insects,  are  toxins  of  animal  origin 
which  have  pathologic  and  scientific  importance. 

4.  "Endogenous'-'  infection  or  "autoinfection."  "Anto- 
By  this  term  we  mean  infection  of  an  individual 
by  micro-organisms  which  reside  naturally  on 
some  surface  of  the  body.  Such  organisms  pro- 
duce infection  only  when  some  other  factor,  par- 
ticularly traumatism,  comes  into  operation. 

Hair  follicles  frequently  contain  staphylococci 
and  when  occlusion  occurs  the  organisms  may  pro- 
duce a  pustule  or  a  furuncle.  An  injury  of  the 
conjunctiva  may  result  in  infection  by  staphy- 
lococci or  pneumococci,  which  are  present  normally, 
and  many  wound  infections  are  due  to  organisms 
which  pre-exist  on.  the  surface. 

Probably  a  factor  of  great  importance  for  the 
invasion  of  such  organisms  is  a  condition  of  low- 
ered resistance  on  the  part  of  the  tissues.  We 
knoTV,  for  example,  that  virulent  streptococci  and 
pneumococci  are  frequently  found  in  the  pharynx 
and  on  the  tonsils  in  apparent  health.  Exposure 
to  cold  in  some  instances  may  be  the  means  of 
lowering  the  resistance  of  the  surfaces  (inhibition 
of  the  antibacterial  forces)  so  that  the  organisms 
become  more  numerous  and  penetrate  the  sur- 
face. Observations  suggest  also  that  the  presence 
of  a  serous  exudate,  such  as  exists  even  in  a  tran- 
sient inflammation,  may  cause  an  increase  in  the 
virulence  of  the  organisms  which  are  bathed  by  it. 
Similar  forces  may  play  a  role  in  the  bronchitis 
and  pneumonia  v/hich  follow  exposure. 

There  seems  to  be  comparatively  little  danger  of 
"autoinfection"  from  pathogenic  bacteria  which 
exist  nonnally  in  the  intestinal  tract,  except  in 


46  INFECTION    AXD    IMMUNITY. 

the  case  of  traumatism,  as  in  incarcerated  hernia, 
or  in  severe  constipation,  or  when  the  normal 
resistance  of  tlie  intestines  has  been  much  dis- 
turbed by  improper  food. 
Relapses.  Sometimes  an  attack  of  a  disease  represents  a 
recrudescence  or  reinfection  by  organisms  which 
have  persisted  at  some  point  following  a  previous 
attack.  Eelapses  of  typhoid  fever  and  recurrences 
of  facial  erysipelas,  and  frequently  the  flaring  up 
of  an  old  (latent)  gonorrhea,  illustrate  this.  Acute 
miliary  tuberculosis,  or  tuberculous  meningitis, 
may  follow  the  escape  of  bacilli  into  the  circulation 
from  an  unsuspected  focus  in  a  peribronchial 
lymph  gland.  This  manifestly  is  not  autoinfec- 
tion  or  endogenous  infection,  since,  even  in  the 
old  latent  foci,  the  infection  dates  back  to  a  prior 
invasion. 


CHAPTER  V. 


Excretion. 


SOURCES   OF   PATHOGEXIC    MICRO-ORGAXISMS 

(Continued.) 
(5)  From  Man  to  Man. 

As  indicated  in  Chapter  I.  there  are  all  degrees 
in  the  facility  with  which  infectious  diseases  are 
transmitted  from  one  person  to  another,  varying 
from  that  in  Avhich  it  is  only  necessary  to  breathe 
the  air  surrounding  a  patient  (scarlet  fever, 
measles^  influenza,  etc.),  to  that  in  which  trans- 
mission never  takes  place  under  ordinary  circum- 
stances (tetanus,  hydrophobia). 

In  some  instances  a  logical  relationship  exists  Relation  of 
between  the  facility  of  transmission,  on  the  one  Method  of 
hand,  and  the  form  of  excretion  of  the  micro-or- 
ganisms and  their  preferred  infection  atrium,  on 
the  other.  Thus  in  many  diseases  in  which  the 
micro-organisms  are  excreted  from  the  respiratory 
passages  the  latter  are  also  used  as  the  infection 
atrium  (influenza,  measles,  smallpox,  etc.).  In 
others,  in  which  they  are  excreted  mainly  by  the 
intestines,  the  infection  atrium  is  the  intestines 
(typhoid,  cholera,  dysentery).  Even  if  it  were 
possible  for  the  organisms  of  typhoid  and  cholera 
to  gain  entrance  through  the  lungs  (and  indeed  it 
may  be  possible  in  typhoid  at  least),  the  fact  of 
their  excretion  mainly  by  the  stools,  and  by  the 
urine  in  typhoid,  would  render  primary  pulmonary 
involvement  difficult.  They  reach  the  intestines 
more  readily  through  contaminated  food,  water, 


Conveyance. 


48  IXFECTIOX    AXD    JMMUXITY. 

etc.,  than  they  could  reach  the  lungs  through  in- 
fected dust  or  droplets.  Similarly,  if  the  virus  of 
scarlet  fever,  which  is  excreted  from  the  lungs  and 
skin,  could  cause  infection  only  through  cutaneous 
wounds,  rather  than  through  the  air  passages,  there 
is  reason  to  believe  it  would  not  hold  its  pres- 
ent position  as  a  ver\^  contagious  disease.  Among 
the  communicable  diseases  we  have  to  recognize 
that  each  has  its  own  mechanism  for  habitual 
transmission,  although  the  habitual  mechanism 
may  be  departed  from  on  many  occasions. 
Mediums  of  As  would  be  supposcd,  the  diseases  which  are 
most  readily  acquired,  the  most  contagious,  and 
the  most  prevalent  are  those  in  which  the  micro- 
organisms are  excreted  into  the  air  from  the  res- 
pirator}^ passages,  and  in  which  also  the  respira- 
tory passages  are  the  preferred  infection  atrium. 
The  medium  of  conveyance — i.  e.,  the  air — is  used 
alike  by  all  individuals.  Some  other  diseases,  much 
less  contagious  than  those  mentioned,  may  pre- 
vail in  extensive  epidemic  form,  often  exceeding 
scarlet  fever,  measles,  etc.,  in  the  percentage  of 
incidence,  as  in  the  cases  of  cholera  and  typhoid 
fever.  This  is  commonly  due  to  an  infected  water 
suppl}^,  and  the  distribution  of  the  disease  cor- 
responds in  large  degree  to  that  of  the  contami- 
nated water.  In  other  words,  the  epidemic  is  co- 
extensive with  the  use  of  the  conveying  medium. 

Similarly,  the  prevalence  of  gonorrhea  and  syph- 
ilis depends  on  the  extent  of  promiscuous  sexual 
intercourse;  and,  of  malaria  and  j^ellow  fever,  on 
the  number  of  individuals  who  become  bitten  by 
the  infec'ted  Anopheles  or  Stegomyia  mosquitoes. 

Thus  the  central  factor  in  the  communication 
of  infection   is  suitable  contact  with  the  agency 


MEDIUMS    OF    CONVEYANCE.  49 

oE  conveyance,  and  where  such  contact  can  be  re- 
alized with  difficulty  communication  from  person 
to  person  rarely  occurs  (e.  g  tetanus  and  hydropho- 
bia, in  which  wound  inoculation  is  required). 

It  is  probable  that  the  air,  in  the  absence  Air  as  ^ 
of  atmospheric  currents,  would  soon  become  ster-  Medium. 
ile,  by  virtue  of  the  effect  of  gravity  in  carrying 
the  microbes  to  the  earth,  and  the  germicidal  ac- 
tion of  sunlight  and  diffuse  light.  Of  course,  these 
conditions  do  not  prevail,  or  are  not  effective,  and 
the  air  stands  as  one  of  the  important  agencies  by 
which  virulent  micro-organisms  reach  the  individ- 
ual, either  from  other  individuals  and  animals  or 
from  inanimate  nature. 

For  a  long  time  it  was  supposed  that  convey- 
ance through  the  air  takes  place  chiefly  or  entirely 
through  the  medium  of  fine  particles  of  dust  which 
are  laden  with  micro-organisms  ("dust  infection") . 
It  was  only  through  fundamental  work  by  Flugge  • 
(1897)  and  others  that  it  was  shown  how  minute 
droplets  of  saliva  or  mucus  from  the  lungs  or  nasal 
passages  are  fully  as  important  as  dust,  and  per- 
haps more  important,  for  the  transfer  of  infection 
from  one  individual  to  another.  This  is  "droplet 
infection." 

The  fields  occupied  by  dust  infection  and  drop-  y^f'^cUon.' 
let  infection  do  not  coincide  exactly.  Only  those 
diseases  can  be  concerned  in  droplet  infection  in 
which  infected  droplets  are  discharged  from  the 
bod}^ — i.  e.,  chiefly  from  the  upper  respiratory  pas- 
sages. Since  the  infective  droplets  of  saliva, 
serum,  mucus  and  pus  may  become  desiccated  and 
pulverized,  the  field  of  dust  infection,  theoretically, 
includes  not  only  those  diseases,  but  also  many 
others.    Thus,  dust  infected  with  the  pyogenic  or- 


50  lyFECTlOy    AXD    IMMUXITY, 

ganisms,  or  with  tetanus  bacilli,  may  be  derived 
from  ordinary  earth  or  earth  contaminated  with 
the  dried  excretions  of  animals.  And  in  other 
cases  dried  and  pulverized  urine  or  feces  (typhoid, 
cholera),  or  desiccated  discharges  from  diseased 
surfaces,  from  sinus  and  abscesses  (tuberculosis, 
erysipelas),  may  give  rise  to  infected  dust.  The 
skin  may  be  an  important  source  of  infected  dust 
in  the  desquamative  diseases  (scarlet  fever,  measles, 
smallpox),  in  that  individual  horny  cells  or  groups 
of  cells  laden  with  organisms  may  float  in  the 
air  with  no  great  velocity  in  the  movement  of  the 
latter. 

The  importance  of  dust  infection  is  curtailed, 
however,  because  of  the  slight  resistance  which 
many  microbes  show  against  desiccation  and  the 
germicidal  action  of  light.  Gotschlich  classifies 
micro-organisms  regarding  the  likelihood  of  their 
participating  in  dust  nfection  as  follows : 
cia.s.ses  of  ^a)  Qr^anisms  which  are  not  capable  of  livinir 
in  dust  as  it  is  dried  in  the  air,  and  hence  never 
(rarely  might  be  better)  can  be  disseminated 
through  dried  particles  (cholera,  plague,  gonor- 
rhea, influenza). 

(b)  Organisms  which  are  capable  of  being  car- 
ried as  dust  for  considerable  distances  by  such 
weak  currents  of  air  as  ordinarily  exist  in  dwell- 
ings, and  which,  when  once  suspended  in  the  air. 
remain  alive  for  a  long  time,  and  easily  lead  to 
dust  infection  (pus  cocci,  p3^ocyaneus,  meningococ- 
cus, anthrax  spores,  tubercle  bacilli  and  tetanus 
bacilli). 

(c)  Organisms  which,  indeed,  are  resistant  to 
desiccation,  but  which  are  disseminated  as  dust 
only  through  stronger  air  currents,  such  as  occur 


DUST  n^FECTIOX.  51 

exceptionally  in  dwellings  (typhoid  and  less  often 
diphtheria). 

This  leaves  out  of  consideration  the  unknown    conditions 
organisms  of  the  exanthemata,  referred  to  above. 
The  conditions  as  they  ordinarily  exist  in  dwell- 
ings are  taken  as  a  standard,  and  the  weight  and 
size  of  the  particles,  and  the  velocity  of  the  air 
in  an  upward  direction,  as  well  as  the  viability  of 
the  different  organisms  in  a  dried  condition,  are 
the  essential  factors  which  govern  the  likelihood 
of  dust  infection,    '^^aturally,  only  those  infected 
particles  of  dried  dust  which  may  be  carried  up- 
ward for  a  considerable  distance  by  a  very  low 
velocity  of  the  air  are  able  to  remain  suspended 
for  some  time  in  the  atmosphere  of  a  room  and, 
consequently,  exist  as  a  protracted  danger  of  air 
infection.     M.  J^eisser  considers  as  the  limit  that 
degree   of   "Verstaubbarkeit"*   in   which   the   in- 
fected particles  may  be  carried  to  a  height  of  80 
cm.  by  an  air  velocity   (upward)    of  1  cm.    (per 
second)."      (Quoted  from   Gotschlich  in  Kolle  & 
Wassermann's  Handbuch  der  Pathogenen  Mikro- 
organisms.  Vol.  1,  p.  168).     After  the  dust  in  a 
room  is  once  thoroughly  stirred  up,  from  one  to 
eight  hours  are  required  for  it  to  settle  completely 
under    the    most    favorable    conditions     (Stern, 
Fliigge,  cited  by  Gotschlich).    Dust  infection  may 
play  a  part  in  public  buildings  and  conveyances 
where  the  currents  of  air  are  stronger  than  they 
ordinarily  are  in  dwellings.     Even  in  dwellings, 
however,  the  conditions  are  by  no  means  uniform. 
More   violent   currents    are   excited   by    a   breeze 
through  an  open  window,  by  the  movemients  of 
persons,  and  the  chances  of  infection  arc  increased 

*  Pulverization. 


52  INFECTION    A^W    IMMUNITY. 

as  a  consequence  of  ^^dusting."  Naturally  the 
longer  the  suspension  within  the  period  of  via- 
bility of  the  organisms  the  greater  the  chance  of 
conveyance. 
Droplet  Droplets  of  saliva,  etc.,  are  discharged  into  the 
air  through  coughing,  sneezing,  laughter,  and  even 
forcible  speaking.  This  does  not  occur  with  ordi- 
nary respiration.  In  coughing  droplets  may  be 
carried  as  far  as  thirty  feet  from  tlie  individual, 
and  they  may  be  carried  much  farther  by  extrane- 
ous currents  of  air.  Such  droplets  may  remain 
suspended  in  the  air  for  approximately  an  hour, 
but  the  period  of  their  suspension  depends  on  their 
size,  the  weight  of  the  organisms  they  carry  and 
the  degree  of  moisture  in  the  air.  In  a  drier  air 
they  become  desiccated  more  quickly  and  after  des- 
iccation fall  more  rapidly. 

Laschtschenko,  and  also  Heymann,  investigated 
the  dissemination  of  tubercle  bacilli  by  coughing 
in  pulmonary  tuberculosis.  In  40  per  cent,  of  the 
cases  guinea-pigs  which  were  placed  even  at  con- 
siderable distances  from  the  patients  contracted 
tuberculosis  of  the  lungs  or  bronchial  lymph 
glands.  The  bacilli  have  been  demonstrated  mi- 
croscopically in  such  droplets  by  numerous  ob- 
servers. Leprosy  bacilli  are  carried  similarly 
(Schaffer). 

On  account  of  their  content  in  mucin  the  drop- 
Jets  adhere  closely  to  solid  surfaces,  where  they 
soon  dry  and  become  harmless  unless  they  are 
disloiged  l)y  some  violence. 

When  contained  in  such  dry  droplets  the  tu- 
bercle bacillus  lives  for  about  three  days  in  the 
light  and  eighteen  days  in  the  dark.  Most  other 
organisms,  except  the  spore-bearing  a^nd  those  cans- 


DROPLET  INFECTIONS. 


53 


ing  some  of  the  contagious  exanthemata,  die  more 
q"uickl3\ 

The  conditions  for  droplet  infection,  then,  are.  conditions. 
in  the  main,  as  follows :  Fii'st,  the  micro-organ- 
isms must  be  discharged  into  the  air,  in  viable 
and  viriTlent  condition,  and  in  sufficient  quantity, 
from  the  respirator}-  passages  of  the  patient.  Sec- 
ond, they  must  be  able  to  retain  life  and  virulence 
for  a  greater  or  less  period  of  time,  after 
being  liberated  in  this  way.  Third,  they  must  be 
able  to  use  some  portion  of  the  respiratory  tract, 
or  the  gastro-intestinal  tract  indirectly  from  the 
respiratory  tract,  as  an  infection  atrium.  Fourth, 
the  advent  of  a  susceptible  person  within  the  zone 
of  infected  atmosphere  which  surrounds  the  pa- 
tient during  the  period  of  viability  and  virulence 
of  the  excreted  organisms. 

In  general  the  same  principles  also  apply  to  dust 
infection  so  far  as  it  concerns  the  ordinary'  "air 
borne"  diseases. 

The  question  is  commonly  raised  as  to  which  Relative 
is  the  more  important,  or  more  prevalent,  dust  in- 
fection or  droplet  infection.  Although  it  is  the 
tendency  at  present  to  assign  a  minor  role  to  dust 
infection,  it  unquestionably  is  of  importance  in 
certain  diseases,  particularly  in  tuberculosis.  The 
situation  may  be  conceived  to  be  as  follows :  In 
relation  to  diseases  caused  by  micro-organisms 
which  have  little  resistance  to  desiccation  and 
light  (e.g..,  plague,  influenza),  droplet  infection, 
implying  proximity  to  the  patient,  is  more  likely 
to  occur  than  dust  infection  (as  in  occupying  a 
room  vacated  by  a  patient  a  longer  or  shorter  pe- 
riod previously).  Concerning  those  caused  by  or- 
ganisms which  have  greater  resistance  to  desicca- 


54  INFECTION    AND    IMMUNITY. 

tion  and  light,  as  in  tuberculosis,  the  importance 
of  dust  infection  approximates,  though  it  may  not 
equal,  that  of  droplet  infection. 
\%"ater  as  Just  as  the  ail  is  the  principal  medium  of  con- 
**Mediiim.  vevancc  for  the  group  of  diseases  discussed  above, 
so  contaminated  water  pla3'S  an  important,  but  not 
the  sole,  part  in  the  transmission  of  another  group. 
Typhoid  and  paratyphoid  fever,  cholera  and  bacil- 
lary  dysentery  are  the  chief  representatives. 

Epidemics  which  arise  in  this  way  are  frequently 
spoken  of  as  "water-borne"  epidemics.  Sometimes 
typhoid  and  cholera  are  called  "water-borne'^  dis- 
eases, but  epidemics  are  so  often  instituted  and 
maintained  by  various  kinds  of  indirect  contact 
that  the  appellation  is  one-sided. 
cniMijtiniis.  Three  essential  conditions  are  required  in  order 
that  a  disease  may  be  more  or  less  habitually 
transmitted  through  water :  First,  tlie  discharge 
of  the  organisms  from  the  bodv  of  the  patient  in 
such  form  tliat  they  may  reach  a  water  supply. 
Second,  the  abilitv  of  the  organisms  either  to  live 
for  a  moderate  length  of  time  in  the  water,  or  to 
proliferate  in  it,  without  losing  virulence.  Third, 
the  utilization  of  the  gastro-intestinal  tract,  the 
upper  respiratory  tract,  or  the  lungs  indirectly 
from  the  latter,  as  an  atrium  of  infection. 

The  hrst  condition  is  readily  realized  in  the  dis- 
eases mentioned,  inasmuch  as  the  micro-organisms 
are  discharged  in  large  numbers  with  the  feces, 
and  also,  in  the  case  of  typhoid  and  paratyphoid, 
with  the  urine. 
sourt-eM  of       All  tvpcs  of  watcr  supplies  may  be  contaminated 

Cnntniniiia-  '^  .  '  \  ^ 

tion.  l)y  these  excretions.  Wnen  the  water  of  a  com- 
munity is  taken  from  a  stream  the  latter  may  be 
infected   ])v   tlTe   sewajre   of    another    community 


VJABILITl    IN   WATER.  55 

higher  np  the  stream,  or  by  the  discharges  of  even 
a  single  patient.  The  throwing  of  typhoid  dis- 
charges on  the  bank  of  a  stream  has  resulted  in 
severe  epidemics.  Eeservoirs  may  be  infected  sim- 
ilarly. In  some  instances  a  city  which  derives  its 
Waaler  from  an  inland  lake  also  empties  its  sewers 
into  the  same  body  of  water.  Even  when  the  sew- 
age outlet  is  qnite  remote  from  the  water  intake, 
surface  currents,  as  caused  by  the  wind,  may  carry 
water,  and  hence  infection,  from  the  former  to  the 
latter.  In  harbors  the  water  may  become  infected 
from  the  sewage  of  a  ship  which  carries  a  case  of 
cholera.  Streams  have  been  contaminated  by 
washing  in  them  the  soiled  linen  of  patients.  When 
excretions  are  thrown  on  the  ground  the  micro- 
organisms have  been  carried  into  wells  by  surface 
water  from  which  small  epidemics  have  arisen. 

The  very  occurrence  of  water-borne  epidemics  viability 
indicates  that  the  micro-organisms  concerned  live 
for  a  longer  or  shorter  period  of  time  in  ordinary 
waters.  Various  factors  influence  their  longevity 
in  water,  and  their  persistence  at  the  point  of  first 
contamination.  Purer  waters  are  not  so  favorable 
for  the  life  of  the  organisms  of  typhoid  and  chol- 
era as  those  which  contain  a  certain  amount  of  or- 
ganic matter  and  salts.  On  the  other  hand,  an  ex- 
cess of  organic  matter  when  accompanied  by  many 
saprophytic  organisms  also  shortens  the  life  of 
these  bacteria,  particularly  when  in  stagnant 
water;  and  this  principle  is  utilized  for  purifica- 
tion of  sewage  in  those  systems  which  involve  the 
use  of  sewage  tanks.  A  rapidly  flowing  stream 
naturally  results  in  purification  more  quickly  than 
one  which  is  sluggish. 


56 


INFECl'IOX    AND    IMMUNITY. 


"Water- 

Uorne"  and 

"Contact" 

Epidemics. 


Conveyance 
by  Food. 


Data  regarding  the  longevity  of  these  organisms 
in  'water  and  milk  are  given  in  the  sections  on 
cholera  and  typhoid. 

"Water-borne"  epidemics  are  characteristic  in 
this,  that  very  many  individuals  are  stricken  sud- 
denly and  simultaneously  and  the  outbreak  is,  at 
first,  limited  to  those  who  are  supplied  by  tlie  in- 
fected water.  "Contact"  epidemics,  on  the  other 
hand,  j^rogress  slowly  and  irregularly,  although 
they  may  finally  reach  large  proportions.  Nat- 
urally an  epidemic  begun  by  contaminated  water 
may  be  maintained  by  contact,  and  continuance  by 
contact  again  offers  opportunity  for  the  fresh  in- 
fection of  water,  milk  and  food.  The  viability  of 
micro-organisms  in  the  excreta,  after  the  discharge 
of  the  latter,  is  important,  both  from  the  stand- 
point of  water  infection  and  that  which  occurs 
by  indirect  contact.  Uffelmann  determined  that 
typhoid  bacilli  may  live  in  the  dejecta  for  many 
months,  and,  at  least  under  some  conditions,  the 
cholera  vibrios  in  the  feces  is  viable  for  two  or 
three  weeks  (Lubarsch). 

As  stated  previously,  diseases  which  are  peculiar 
to  man  may  be  distributed  by  milk  which  has  been 
contaminated  by  convalescents  (as  in  scarlet  fever) 
or  by  "carriers,"  or  by  some  others  indirectly  from 
these,  or  by  infected  water  used  in  washing  con- 
tainers. Epidemics  caused  by  infected  milk  are, 
in  miniature,  similar  to  those  arising  from  a  con- 
taminated water  supply,  their  distribution  coin- 
ciding with  the  area  of  consumption  of  the  milk. 

Other  food  substances  act  as  carrying  agents 
only  when  they  become  infected  accidentally,  as  by 
flies,  washing  in  contaminated  water,  or  by  con- 
valescents and  "carriers." 


CONVEYANCE    BY    CLOTHING,  ETC.  57 

Transmission  by  direct  and  indirect  contact  are  contact. 
somewhat  in  contrast.  In  the  former  actual  per- 
sonal contact  takes  place  between  the  sick  and 
healthy^  as  previously  stated,  and  as  illustrated  by 
gonorrhea  and  syphilis.*  Probably  many  of  the 
infections  which  are  conveyed  through  the  air  may 
also  be  acquired  by  direct  contact.  However,  a 
distinction  in  this  case  has  no  significance,  since 
actual  contact  without  exposure  to  air  infection 
could  hardly  occur. 

Indirect  contact,  on  the  other  hand,  implies 
transmission  through  the  agency  of  an  interme- 
diate person  or  object.  Speaking  strictly/ convey- 
ance from  person  to  person,  through  the  air,  water, 
or  even  by  insects,  comes  within  the  domain  of  in- 
direct contact,  yet  their  methods  are  so  specialized, 
so  obtrusive  and  so  constantly  utilized  by  certain 
groups  of  micro-organisms  that  they  deserve  the 
separate  consideration  usually  given  them.  The 
tendency  is  a  correct  one  to  withdraw  from  the 
domain  of  indirect  contact  any  method  of  trans- 
mission which  can  be  spoken  of  more  concretely. 

One  could  not  hope  to  mention  all  of  the  possi- 
ble channels  through  which  an  infection  may  be 
carried  indirectly.  There  are  great  variations  in 
details.  "Carrying  a  disease  in  one's  clothing" 
from  place  to  place;  the  use  of  the  to3^s  of  a  diph- 
theritic child;  washing  or  handling  the  linen  of  a 
cholera,  typhoid  or  dysentery  patient ;  occupying  a 
room  formerly  used  by  a  patient  having  scarlet 
fever  or  tuberculosis;  the  occasional  transfer  of 
syphilis  by  the  drinking-cup  or  the  dentist's  for- 


*  Exceptions  occur  in  relation  to  syphilis,  as  in  the  oc- 
casional transfer  by  drinking  cups  and  instruments ; 
hereditary    syphilis    may    be    considered    as    a    special    case. 


58  INFECTION    AND    IMMUNITY. 

ceps;  the  former  occurrence  of  contagious  hospital 
gangrene  through  contamination  of  dressings  and 
of  other  infections  from  patient  to  patient  through 
unclean  instruments  or  hands;  these  are  examples 
of  conveyance  by  indirect  contact. 

As  some  of  them  show^  diseases  which  are  ha- 
bitually transmitted  through  tlie  air  (scarlet  fever) 
or  by  water  (typhoid,  cholera)  may  also  be  trans- 
ferred by  indirect  contact. 
Hereditary  In  the  strict  zoolo2fical  sense  no  form  of  trans- 
sion.  mission  of  an  infection  from  parent  to  offspring 
can  be  viewed  as  truly  hereditary,  since  inheritance 
concerns  only  properties  which  are  inherent  in  the 
germ  cells  and  their  chromatin.  Micro-organisms 
are  foreign  and  their  introduction  in  the  germ 
cells  from  the  parent  can  only  be  considered  as 
accidental.  It  is,  then,  only  for  the  sake  of  con- 
venience and  for  lack  of  a  more  exact  term  that 
the  inheritance  of  infections  is  spoken  of.  This 
distinction  has  been  strongly  emj)hasized  by  Han- 
sen (Virch.  Arch.,  Vol.  120)  and  by  Lubarsch 
(Ibid.,  Vol.  124).  Some  of  the  metabolic  diseases 
and  functional  derangements,  on  the  other  hand, 
may  be  truly  inherited,  or,  perhaps  better,  a  ten- 
dency or  predisposition  to  them  may  be  inherited. 
Also,  it  is  very  probable  that  susceptibility,  or,  on 
the  other  hand,  resistance  to  some  particular  infec- 
tion, may  be  inherited,  thus  accounting  for  the 
frequent  or  rare  occurrence  of  some  infections  in 
a  given  family. 
(jieriii  Cell  When  disease  of  the  offspring  can  be  referred  to 
a  ]u-imary  invasion  of  the  germ  cells  (ovum  or 
sperm  cells)  by  micro-organisms  it  is  said  to  have 
originated  by  "germ  cell  infection."  It  is  not 
definitely  known  that  this  type  of  hereditary  trans- 


it! feet  ion. 


GERM    CELL    INFECTION.  59 

mission  talves  place  in  man.  and  the  likelihood  of 
its  occurrence  could  be  proved  only  by  finding  the 
micro-organisms  actually  within  the  ovum  of 
sperm  cell. 

Definite  examples  of  this  type  of  transmission 
are  found  in  insect  life,  particularly  among  ticks. 
The  piroplasmas  of  Texas  fever  and  of  Ehodesian 
fever  of  cattle,  the  spirillum  of  South  African 
tick  fever  of  man,  and  the  virus  of  Eocky  Moun- 
tain spotted  fever  are  all  transmitted  to  the  lar- 
vae of  the  next  generation  through  infection  of 
the  ova  of  the  corresponding  ticks. 

Since  it  does  occur  in  other  fonns  of  life,  it 
would  not  be  surprising  if  it  also  occurs  in  man. 
In  that  form  of  inherited  syphilis  in  which  the 
child  derives  the  infection  from  the  father,  the 
mother  apparently  remaining  uninfected,  the  virus 
may  have  been  introduced  into  the  ovum  by  means 
of  an  infected  sperm  cell.  Even  in  this  case,  how- 
ever, it  is  virtually  impossible  to  rule  out  the  exis- 
tence of  a  latent  infection  of  the  mother.  And  if 
such  infection  does  exist,  the  spirochetes  may  have 
reached  the  embryo  by  way  of  the  placenta,  in- 
stead of  through  the  ovum.  Possibly  the  recently 
discovered  test  for  S3'philis  (fixation  of  comple- 
ment) will  throw  some  light  on  this  phase  of  in- 
herited syphilis,  since  it  renders  possible  the  diag- 
nosis of  the  disease  in  the  mother  reofardless  of 
positive  clinical  manifestations. 

It  is  equally,  or  perhaps  more,  uncertain  as  to 
whether  tuberculosis  is  ever  inherited  through  in- 
fection of  the  germ  cells.  Tubercle  bacilli  have 
been  found  in  the  testicular  secretion  in  both  man 
and  animals.  In  such  cases  the  tuberculosis  is  of 
an  advanced  type,  resulting  in  early  death.    Even 


Transmis- 
sion. 


00  INFECTION    AND    IMMUNITY. 

if  some  of  the  bacilli  were  actually  within  the 
sperm  cells  and  capable  of  introduction  into  the 
ovum  through  them,  the  great  preponderance  of 
the  spermatozoa  over  the  bacilli  renders  infection 
of  the  ovum  improbable.  In  one  such  case  Gartner 
estimated  the  numerical  relation  of  the  bacilli  to 
the  spermatozoa  as  one  to  22.7  million,  hence  the 
impregnating  cell  would  very  likely  be  an  unin- 
fected one. 

It  has  sometimes  been  assumed  that  leprosy  may 
be  transmitted  in  this  way,  but  there  is  no  strong 
evidence  in  support  of  it. 
Placental  Infection  of  the  embryo,  from  the  mother,  by 
way  of  the  placenta,  has  been  demonstrated  experi- 
mentally, and  encountered  clinically,  unmistakably. 
Opinions  differ  as  to  whether  actual  involvement 
— i.  e.,  infection  or  defects — of  the  placenta  is 
prerequisite  to  the  passage  of  micro-organisms 
from  the  mother  to  the  embryo. 

M.  Wollf,  on  the  basis  of  experimental  work  with 
the  anthrax  bacillus,  concluded  that  the  uninjured 
placenta  is  an  effective  barrier  against  such  a 
transfer.  It  was  supposed,  however,  that  injuries 
of  the  placenta  which  resulted  in  bleeding,  thus 
establishing  a  temporary  connection  between  the 
circulations  of  the  mother  and  fetus,  as  well  as 
other  lesions  metastatic  in  character,  could  well 
result  in  infection  of  the  embryo.  Many  others 
also,  on  the  basis  of  experimental  work  and  the 
study  of  human  material,  concluded  that  there 
must  be  recognizable  lesions  of  the  placenta  to 
permit  transfer  from  mother  to  child.  The  bacil- 
lus of  chicken  cholera,  a  member  of  the  hemor- 
rhagic septicemia  group  of  organisms,  causes  hem- 
orrhages in  the  placenta  in  animals  and  is  trans- 


PLACENTAL    TRANSMISSION.  CI 

mittecl  to  the  embryo  (Malvoz).  Tuberculosis  oc- 
casionally, and  syphilis  very  often,  attack  the  pla- 
centa in  man.  In  a  number  of  instances  fetuses 
have  been  born  with  the  eruption  of  smallpox 
derived  from  the  mother  and  the  transfer  of  ty- 
phoid bacilli  through  the  placenta  has  been  ob- 
served occasionally.  Similar  transmission  in  man 
has  been  noted  in  relation  to  anthrax,  pneumonia, 
recurrent  fever,  and  infections  with  the  pyogenic 
cocci.  Abortions,  due  either  to  infection  or  intox- 
ication, may  occur  during  most  of  the  acute  fe- 
brile infections. 

Contrary  to  the  view  expressed  above,  Baum- 
garten,  Birch-Hirschfeld,  Lubarsch  and  many 
others  conceived  that  a  pre-existing  injury  of  the 
placenta  is  not  essential  for  transfer;  that  the 
micro-organisms,  especially  when  present  in  the 
blood  in  considerable  numbers,  as  in  anthrax,  may 
"grow  through"  the  placental  vessels  in  the  absence 
of,  and  without  causing,  anatomical  lesions. 

It  is  extremely  probable  that  both  views  are  cor- 
rect, but  perhaps  in  relation  to  different  types  of 
micro-organisms.  It  has  been  demonstrated  many 
times,  clinically  and  experimentally,  that  tubercle 
bacilli  will  pass  through  the  intestinal  mucosa  into 
the  adjacent  lymphatics  without  causing  lesions 
of  the  mucosa,  and,  although  the  conditions  are  not 
identical  in  the  two  structures  (migration  of  wan- 
dering cells  through  intestinal  wall ! ) ,  the  occur- 
rence in  one  suggests  its  possibility  in  the  other. 
However,  the  existence  of  the  phenomenon  is  so 
thoroughly  established  as  to  render  the  exact  mech- 
anism a  more  or  less  secondary  matter. 

It  is  an  important  theory  of  Baumgarten's  that   Latent 
tubercle  bacilli  which   are  acquired  during  fetal   infection. 


62  l'NFEGT101\^    AND    IMMUNITY. 

life  ma}'  remain  latent  until  puberty  and  then, 
when  the  unusual  resistance  which  is  coincident 
with  rapid  growth  has  subsided,  the  bacilli  mul- 
tiply and  tuberculosis  manifests  itself.  He  sup- 
poses also  that  an  intermediate  generation  may, 
without  showing  tuberculosis  itself,  transmit  the 
disease  to  the  next  generation  ( Ueherspringung  von 
Generationcn) .  This  would  seem  to  presuppose 
the  occurrence  of  germ-cell  infection,  but  perhaps 
not  necessarily  so.  As  having  a  possible  bearing 
on  Baumgarten's  hypothesis,  it  has  been  found  by 
Harbitz,  by  Wechselbaum  and  others  that  tubercle 
bacilli,  particularly  in  children,  may  exist  in  the 
lymph  glands  without  causing  anatomical  changes. 
This  view  has  several  strong  supporters,  and  it 
is  thought  that  the  bacilli  may  remain  latent  in 
any  portion  of  the  body.  That  hereditary  syph- 
ilis may  remain  latent  for  many  3'ears  is  well 
known. 

On  the  other  hand,  it  is  more  generally  believed 
that  tuberculosis  in  most  instances  is  a  postnatal 
acquisition  (Koch,  Cornet  and  others)  and  ra- 
tional prophylaxis  naturally  must  be  based  on  this 
conception.  Extensive  involvement  of  the  liver 
and  periportal  lymph  glands  is  characteristic  of 
the  placental  transmission  of  tuberculosis.  The  be- 
lief is  occasionally  expressed  that  leprosy  may  be 
inherited,  possibly  through  placental  transmission, 
but,  in  view  of  the  non-susceptibility  of  animals 
and  failure  to  cultivate  the  bacillus,  the  question 
cannot  be  taken  up  experimentally.  The  possibil- 
ity of  infection  of  the  embryo  directly  from  the 
father  during  coitus  is  discussed,  but  there  is  no 
definite  proof  of  its  occurrence. 


HEREDITARY    ISFECTIO^.  63 

It  is  conceivable  that  micro-organisms  may  pass 
from  the  mother  to  the  child  by  way  of  the  blood 
through  the  placenta  at  the  inception  of  labor  dur- 
ing an  early  stage  of  separation  of  the  placenta 
from  the  uterine  wall. 

Infection  of  a  child,  as  with  gonorrheal  ophthal- 
mia, during  delivery  is  not  regarded  as  an  ex- 
ample of  "inheritance"  of  disease.  It  is  an  extra- 
uterine process,  a  congenital  infection. 


CHAPTEE  VI. 


SOURCES  OF  PATHOGENIC   MICRO-ORGANISMS 

(Concluded.) 

(6)   Dissemination  and  Transmission  hy  Insects. 
A.  Dissemination. 

Role  of       The  demonstration  that  insects  may  play  a  role 

insectn.  ^^  ^-^q  transmission  and  maintenance  of  infections 

dates   from  the  work   of   Smith   and   Kilbonrne, 

which  disclosed  the  relation  of  the  tick  (Margaro- 

pus  annulatus)  to  Texas  fever  in  cattle. 

Insects   may   act   simply   as    disseminators    of 

virus,    or    as    the    agents    of    actual    inoculation 

through  their  bites — i.  e.,  as  transmitters.     It  is 

important  to  keep  this  distinction  in  mind. 

Biologic  and       In  their  role  as  pure  disseminators  they  may 

Meclianioal  .  .  „  ■     ,     , 

Transmission,  carry  micro-organisms  irom  one  point  to  another 
on  their  feet,  mouth  parts,  or  in  their  intestinal 
contents ;  or,  they  may  act  as  temporary  hosts,  the 
microbes  proliferating  in  their  intestinal  tract  and 
subsequently  being  deposited  with  the  feces,  in  in- 
creased numbers,  at  some  new  point.  The  first  is 
pure  mechanical  dissemination,  whereas  in  the  sec- 
ond a  biologic  factor  enters,  that  of  proliferation, 
and  it  may  be  spoken  of  as  biological  dissemina- 
tion. For  example,  when  flies  carry  typhoid  bacilli 
or  cholera  vibrios  from  feces  to  food,  on  their  feet 
or  mouth  parts,  or  tubercle  bacilli  from  sputum  to 
food  or  other  objects,  this  is,  of  course,  a  purely 
mechanical  process.  It  would  be  complicated  by 
the  biological   feature,  however,   in   case   the   or- 


FLY    TRAXSMIHSJOX.  Co 

ganisms,  after  ingestion  by  the  fly,  then  multi- 
plied, and  were  deposited  in  larger  numbers  in 
fly-specks.  It  is,  indeed,  a  difficult  point  to  deter- 
mine whether  or  not  proliferation  of  these  micro- 
organisms actually  takes  place  in  the  intestines  of 
the  fly.  Observations  by  Spillman  and  Haushalter, 
Hofmann,  Celli,  Hayw^ard,  Lord  and  others  have 
shown  conclusively  that  house-flies  ingest  tubercle 
bacilli  from  the  sputum  of  patients  and  excrete 
them  in  their  feces.  The  observations  of  Lord^ 
suggest,  but  do  not  actually  prove,  that  the  bacilli 
multiply  in  the  intestines.  It  has  been  demon- 
strated several  times,  by  inoculation  into  guinea- 
pigs,  that  the  bacilli  in  the  fly-specks  are  virulent. 
The  specks  dry  quickly  and  there  is  little  danger 
of  the  organisms  taking  part  in  dust  infection  un- 
less the  specks  are  violently  dislodged,  and  they 
die  in  a  few  days.  On  the  other  hand,  there  may 
be  a  real  danger  from  the  deposition  of  the  specks 
on  food  (Lord),  which  suggests  a  point  in  pro- 
phylaxis. 

Similar  questions  are  raised  also  in  the  relation 
of  the  fly  to  typhoid,  cholera,  dysentery  and  plague. 
The  importance  of  the  fly  in  the  mechanical  dis- 
semination of  typhoid  bacilli,  resulting  in  exten- 
sion of  epidemics,  is  now  well  established,  as  illus- 
trated by  the  observations  of  Alice  Hamilton,  and 
the  inquiry  into  the  prevalence  of  typhoid  fever 
in  the  American  troops  during  the  Spanish- Amer- 
ican war.  The  conditions  are  similar  in  relation 
to  cholera.  Concerning  dysentery  it  is  considered 
probable  that  flies  are  a  factor  in  distribution,  al- 
though the  point  has  not  been  positively  demon- 
strated.   It  is  uncertain  whether  the  organisms  of 

1.  Reports  of  the  Massachusetts  General  Hospital. 


The  Flea  and 
Plague. 


66  INFECTION    AXD    IMMUNITY. 

typhoid  and  cholera  proliferate  in  the  intestines  of 
the  fly.  It  seems  not  unlikely  in  the  case  of  t}^- 
phoid,  inasmuch  as  Ficker^  found  them  in  the  fly 
twenty-three  days  after  a  feed  on  the  bacilli.  Tsu- 
zuki^  cultivated  cholera  vibrios  from  flies  which 
were  taken  in  the  dwellings  of  patients. 

It  seems  probable  that  flies,  in  some  instances, 
may  distribute  plague  bacilli  after  they  have  them- 
selves become  infected  by  feeding  on  the  sputum 
of  pneumonic  patients  or  on  the  cadavers  of  rats 
dead  of  the  disease.  Yersin*  found  plague  bacilli 
in  flies  dying  in  a  laboratory  in  Avhich  plague  was 
being  studied,  and  in  Xuttall's^  experiments  they 
became  infected  by  feeding  on  diseased  organs. 

The  flea,  on  the  other  hand,  appears  to  act  both 
as  a  disseminator  and  as  a  transmitter  of  plague. 
The  human  flea,  at  least  two  species  of  rat  fleas, 
and  the  flea  of  the  dog  and  cat  readily  become  in- 
fected by  feeding  on  rats  during  the  stage  of  septi- 
cemia in  the  latter,  the  bacilli  multiply  for  a  few 
days  in  their  stomach  and  intestines,  and  are  ex- 
creted in  large  numbers  in  their  feces.  They  are 
able  to  communicate  the  disease  to  other  animals 
by  biting  for  at  least  three  days  after  their  infec- 
tion, but  in  a  short  time  the  bacilli  disappear  from 
their  alimentary  tract  and  they  lose  the  power  of 
transmission.  The  organisms,  which  are  excreted 
in  their  feces,  are  virulent,  and  are  able  to  produce 
infection  through  very  small  abrasions  and 
through  the  minute  wounds  made  by  the  bites  of 
these  insects.  The  deposition  of  bacilli  in  the  feces 
of  the  flea  on  the  skin  of  a  person  is  a  question 

2.  Arch.  f.  Hyg.,  1903.  xlv,  247. 

3.  Arch.  f.  Schififs-u.  Tropenhygiene,  February,  1904,  viii 

4.  Ann.  de  I'Inst,  Past.,  1904,  i.  662. 

5.  Centralbl.  f.  Bakteriol.,  1897,  Abt.  I.  xxii.  87. 


INSECTS    AXD    PLAGUE.  67 

of  dissemination,  whereas  the  injection  of  the  or- 
ganisms through  the  proboscis  is  one  of  inocula- 
tion. The  flea  appears  not  to  "undergo  a  gen- 
eralized infection  with  the  plague  bacillus. 

It  is  possible  that  rats  may  become  infected 
with  plague  also  b}'  the  eating  of  fleas  which  con- 
tain bacilli,  although  this  has  not  yet  been  demon- 
strated. Experimentally  the  disease  has  been  pro- 
duced in  rats  by  feeding  them  infected  tissues  or 
cultures. 

Verjbitski  also  found  that  the  bedbug  behaves  in  '^'»^  Bedbngr. 
a  manner  exactly  similar  to  the  flea  in  the  case  of 
plague.  In  actual  epidemics,  however,  it  seems 
probable  that  this  insect  would  be  concerned  only 
in  the  transmission  of  the  disease  from  man  to 
man,  and  not  from  rat  to  man.  ^^ 

With  the  exception  of  the  last  paragraph  the 
above  concerns  the  mere  dissemination  of  micro- 
organisms by  insects.  As  noted,  the  diseases  con- 
cerned are  bacterial  in  nature  rather  than  proto- 
zoan. Pathogenic  protozoa  may  be  excreted  by  in- 
sects, but,  if  so,  the  event  appears  to  be  without 
practical  significance,  either  because  the  organisms 
are  not  viable  when  excreted,  or  are  not  in  a  stage 
of  development  to  render  them  infective,  or,  what 
is  more  probable,  that  they  find  no  infection 
atrium  when  in  this  condition.  Those  protozoa 
which  are  transmitted  by  insects  usually  require 
actual  inoculation  in  order  that  they  may  cause 
infection. 

B.  Trmismission 
Our  knowledge  is  by  no  means  complete  on 
the  subject  of  insect  transmission,  as  a  whole,  al- 
though the  essential  facts  have  been  worked  out 
in  a  number  of  instances,  as  in  Texas  fever,  some 


68  INFECTIOX    ASD    IMMUNITY. 

other  piroplasmoses,  and  in  malaria.  In  some  in- 
stances it  is  the  micro-organism  which  is  unknown 
(yellow  fever,  dengue),  in  others  the  question  of 
inheritance  in  the  insect  (tr3'panosomiasis),  in 
others  the  relation  of  the  insect  and  the  disease  to 
hosts  other  than  man,  etc. 
Diseases       Discascs  wliich   are   transmitted   habitually,   or 

Transniitteu  -J  ^ 

by  Insects,  mainly,  by  insects  sometimes  possess  rather  dis- 
tinctive epidemiologic  features.  Malaria  occurs  in 
swampy  regions  in  which  certain  species  of  Ano- 
pheles abound.  The  distribution  of  yellow  fever, 
and  indeed  of  all  the  insect-borne  diseases,  coin- 
cides with  that  of  the  insects  which  are  concerned 
in  the  distribution.  In  the  temperate  and  subtrop- 
ical countries  such  diseases  tend  to  prevail  in  the 
warmer  months  and  to  disappear  on  the  advent 
of  frost  or  cooler  weather,  an  event  which  is  cor- 
related with  the  activity  or  inactivity  of  the  insects 
during  these  seasons.  The  Indian  plague  commis- 
sion finds  that  an  epidemic  wanes  when  the  mean 
daily  temperature  is  below  50°  F.,  presumably  be- 
cause the  flea  does  not  become  infected  so  readily 
under  this  condition  :  the  rats  die  before  the  advent 
of  intense  septicemia,  and  without  the  latter  the 
flea  is  less  likely  to  become  infected.  The  flea 
may  also  be  less  likely  to  feed  generously  in  the 
cooler  weather.  Also  it  was  found  that  a  mean 
daily  temperature  of  85°-90°  F.  coincides  with  the 
decadence  of  an  epidemic,  and  in  harmony  with 
this  it  appears  that  the  flea  remains  infective  for 
a  much  shorter  time  at  this  temperature.  When 
virtually  all  the  rats  of  a  locality  have  either 
been  killed  by  plague,  or  have  recovered  from  it, 
those  which  remain  are  for  the  most  part 
Immune,  and  the  conditions  for  a  recrudescence 


IX SECT    TRAXSMISSION.  69 

of  an  epidemic  will  not  be  ripe  until  a  new  gen- 
eration of  rats  has  been  bred.  The  immune 
rats  do  not  harbor  plague  bacilli,  and  hence 
cannot  infect  fleas.  Eocky  Mountain  spotted 
fever  prevails  only  in  the  months  of  spring.  At 
this  time  the  tick  which  acts  as  transmitter  is  in 
its  adult  stage  and  readily  feeds  on  man  as  well  as 
on  other  animals.  The  larval  and  nymphal  stages 
appear  at  other  seasons,  and,  although  their  bites 
are  infective,  they  rarely  feed  on  man,  either  from 
lack  of  opportunity  or  because  of  a  preference  for 
other  hosts  during  these  stages.  The  observation 
of  Carter,  that  when  yellow  fever  patients  are  first 
imported  into  a  new  district  a  definite  period 
(tw^o  to  three  weeks)  elapses  before  new  cases  de- 
velop, suggested  some  novel  mode  of  transmission, 
which  eventually  was  proved  true  when  Eeed,  Car- 
rol and  Agramonte  proved  by  experimentation  the 
correctness  of  the  mosquito  theory  of  Carlos  Fin- 
lay  and  worked  out  the  details  of  transmission. 

For  some  time  it  was  supposed  that  insects 
transmit  only  those  diseases  which  are  caused  by 
protozoan  organisms.  This  impression  arose  from 
the  fact  that  the  first  examples  of  definitely  proved 
insect  transmission  concerned  protozoan  diseases, 
as  Texas  fever  (a  piroplasmosis)  of  cattle,  malaria 
of  man  and  birds,  and  more  recently  the  try- 
panosomatic  diseases. '  It  is  only  since  the  rela- 
tionship of  the  flea  to  plague,  of  the  tick  to  the 
South  African  tick  fever  of  man,  and  of  other 
mites  to  spirilloses  of  animals  that  the  importance 
of  insects  in  transmitting  bacterial  diseases  has 
been  recomized.  contagioas- 

.  .  .  f,  .  .       ness    Sima- 

It  IS  an  interesting  fact  that  contasjiousness  is  lated  by  in- 

sect    Trans— 

sometimes  simulated  in  a  disease  which  is  trans-   mission. 


70  INFECTION    AND    IMMUNITY. 

mitted  only  by  insects.  Thus,  for  many  years,  yel- 
low fever  was  held  to  be  so  contagious  that  not 
only  direct  transfer  from  person  to  person  was 
admitted,  but  also  through  various  indirect  means 
as  by  fomites.  Typhus  fever  has  often  been  cited 
as  tlie  most  contagious  of  all  infections,  yet  mod- 
ern studies  point  rather  strongly  to  an  exclusive 
insect  transmission  (perhaps  fleas  or  bedbugs). 
The  conditions  in  plague  seem  to  be  somewhat 
more  complex,  in  that  both  insect  transmission 
(fleas)  and  contagiousness  prevail,  the  latter  com- 
ing into  play  in  the  pneumonic  form  of  the  dis- 
ease. Dengue,  which  spreads  like  wild  fire,  pos- 
sibly is  transmitted  only  by  the  bites  of  certain 
mosquitoes. 

In  some  instances  the  role  of  the  insect  is  an  ob- 
ligate one — i.  e.,  transmission  can  occur  in  no  other 
way  than  by  its  bite.  This  is  pre-eminently  true 
of  malaria,  which,  virtuallv,  is  incapable  of  trans- 
mission from  person  to  person  even  when  malarial 
blood  is  injected  into  a  healthy  person.  The  par- 
asite when  it  leaves  the  body  becomes  infective  for 
man  again  only  after  it  has  completed  a  sexual 
development  in  the  mosquito.  In  some  instances 
infection  may  be  carried  from  person  to  person 
or  animal  to  animal  by  the  injection  of  diseased 
blood,  yet  under  natural  conditions  the  role  of  the 
insect  is  an  obligate  one  (yellow  fever,  sleeping 
sickness,  Eocky  Mountain  spotted  fever).  The 
flea  in  plague  transmission  is  an  example  of  a 
facultative  role,  since,  as  stated,  this  insect  is  not 
the  only  natural  means  by  which  the  disease  is 
conveyed  from  person  to  person. 
Sources  of  Insccts  which  Carry  and  transmit  infections  nat- 
infection.  urally   must  have   some  source   from   which   they 


SOURCES    OF    INSECT    INFECTION.  71 

derive  the  micro-organisms.  Commonly,  the  trans- 
mission occurs  only  between  different  members  of 
the  same  species :  the  insect  obtains  the  virus  from 
one  individual  and  inoculates  it  into  another.  In 
so  far  as  is  known,  man  alone  suffers  from  yellow 
fever,  and  the  human  type  of  malaria,  and  he 
constitutes  the  only  source  of  infection  for  the 
mosquitoes  which  are  concerned  in  the  mainte- 
nance of  these  diseases.  The  same  conditions  ap- 
pear to  prevail  regarding  piroplasmosis  in  cattle 
(Texas  fever)  and  in  other  animals,  and  also  in 
the  South  African  tick  fever  of  man  (a  spirillosis), 
diseases  in  which  ticks  are  transmitters.  Pre- 
sumably this  is  also  true  of  some  other  insect- 
borne  diseases  among  animals,  as  the  spirillosis  of 
fowls  and  geese. 

In  some  other  instances  the  existence  of  a  third 
host  has  been  demonstrated.  Man  is  an  important 
source  of  infection  for  the  flies  which  carry  sleep- 
ing-sickness, but  the  evidence  is  strong  that  some 
of  the  native  animals  of  Africa  also  harbor  the 
trypanosome  concerned  and  that  tsetse  flies  be- 
come infected  from  them  as  well  as  from  man.  In 
Eoclv}'  Mountain  spotted  fever  man  is  virtually  a 
negligible  factor  for  the  infection  of  the  ticks. 
The  circumstances  indicate  that  one  or  more  spe- 
cies of  small,  wild  animals,  of  demonstrated  sus- 
ceptibilit}',  are  the  means  of  keeping  the  diseases 
alive  in  the  ticks.  It  appears  to  play  back  and 
forth  from  tick  to  animal,  and  it  is  only  occa- 
sionally that  an  infected  tick  becomes  attached  to 
man.  Fleas  probably  derive  the  micro-organisms 
of  plague  from  rats,  in  large  measure,  but  experi- 
ments also  show  that  they  may  become  infected 
from  man. 


72  IXFECTIOy    AyD    IMMrXITY 

Aside  from  the  sources  mentioned,  the  possibil- 
ity also  exists,  in  relation  to  some  infections,  that 
the  viruses  are  native  to  the  insects,  or,  rather, 
that  they  are  habitual  parasites  in  them,  just  as 
the  colon  bacillus  is  a  constant  inhabitant  of  the 
intestinal  tract  of  man.  Even  in  this  case,  ho\y- 
ever,  we  must  assume  either  some  extraneous 
source  for  the  organisms  or  that  they  are  inherited 
from  the  preceding  generation  of  insects.  The  lat- 
ter, indeed,  is  a  method  of  acquisition  which  has 
been  shown  to  occur  in  ticks,  in  relation  to  the 
Texas  fever  of  cattle,  and  the  South  African  tick 
fever,  and  Eocky  Mountain  spotted  fever  of  man. 
The  eggs  of  infected  females  contain  the  respective 
micro-organisms  and  the  larvae  which  hatch  from 
them  are  infective. 
Factors  in  The  factors  which  enable  an  insect-borne  disease 
^'S£"mseas*e*!  ^^  ^^^  maintained  from  year  to  year  vary  a  good 
deal  in  different  cases.  Chronicity,  in  either  the 
animal  or  insect  host,  or  in  both;  inheritance  of 
the  disease  in  the  insect,  and  a  rapid  alternation 
of  the  infection  between  the  insect  on  the  one  hand 
and  the  animal  host  on  the  other — these  seem  to 
be  the  important  conditions  which  have  a  bearing 
on  maintenance  in  one  disease  or  another,  and  all 
of  them  assure  a  more  or  less  constant  source  for 
the  fresh  infection  of  the  carriers. 

Texas  fever  of  cattle  and  other  piroplasmatic 
infections,  malaria,  and  sleeping-sickness  are 
chronic  infections  in  both  the  animal  and  insect 
hosts.  Each  exists  as  a  more  or  less  protracted 
source  of  infection  for  the  other.  In  addition. 
Texas  fever,  and  some  other  piroplasmoses,  are 
hereditary  infections  in  the  tick-carriers,  and  in 
this  way  infection  is  readily  kept  alive  from  one 


ROCKY    MOUNTAIN    FEVER.  73 

season  to  the  next.  It  is  not  yet  known  whether 
sleeping-sickness  is  inherited  in  the  tsetse  fly.  Ma- 
laria is  not  so  transmitted  in  the  mosquito. 

There  may  be  varying  grades  of  chronicity  in  soatii  African 
both  the  animal  and  insect  hosts.  Thus  South  Af- 
rican tick  fever  of  man  (a  spirillosis)  is  semi- 
chronic,  consisting  of  several  recurrences  followed 
by  recovery,  and  it  is  probable  that  the  tick  maj 
acquire  the  disease  from  the  patient  during  any 
one  of  the  recurrences.  In  the  tick,  however,  the 
disease  is  chronic  and  hereditary. 

In  these  cases  the  method  of  maintenance  is 
clear,  and  in  the  presence  of  a  sufficient  number 
of  insects  the  conditions  are  favorable  for  a 
thorough  infection  of  the  inhabitants.  Thus  it  is 
that  in  many  tropical  districts  there  are  none  who 
do  not  fall  victims  to  malaria  sooner  or  later. 

In  Eocky  Mountain  spotted  fever  we  have  an  Rocky  Moun- 
example  of  a  condition  in  which  the  disease  is  i^ever. 
acute  in  the  various  animal  hosts,  including  man, 
but  chronic  in  the  carrier,  the  tick.  In  order  that 
fresh  ticks  may  acquire  the  disease  it  is  necessary 
for  them  to  feed  on  a  susceptible  animal  in  com- 
pany with  infected  ticks,  or  shortly  following  a 
feed  by  the  latter.  Since  several  hundred  larva? 
or  nymphs  may  be  found  on  one  of  these  animals 
at  the  same  time,  it  is  readily  seen  how  this  may 
be  accomplished.  While  certain  of  the  small  ani- 
mals (ground-squirrel,  ground-hog,  rock-squirrel, 
and  perhaps  others)  are  in  hibernation  the 
virus  still  lives  in  the  eggs,  larvse  and  nymphs; 
and  when  the  animals  "come  out"  in  the  spring 
certain  of  them  become  infected  through  the  bites 
of  the  larvas  or  nymphs  and  then  are  in  condition 
to  infect  fresh  ticks.     Hence  the  disease  is  kept 


74  INFECTION    AND    IMMUNITY. 

alive  through  inheritance  in  the  tick  during  the 
months  of  winter,  and  at  other  times  through 
alternation  from  tick  to  animal  and  animal  to  tick. 
Man  plays  little  or  no  role  in  its  maintenance,  and 
his  occasional  infection  through  the  tick  bite  may 
be  regarded,  in  a  sense,  as  an  unessential  incident. 

YellovA^  fever,  again,  illustrates  the  condition  of 
an  acute  infection  in  the  animal  host  (man)  and 
a  chronic  in  the  insect  (Stegomyia  calopus). 
Like  Eocky  Mountain  spotted  fever,  the  virus  of 
yellow  fever  is  transmitted  in  a  hereditary  man- 
laer  to  the  next  generation  of  mosquitoes  (Mar- 
choux  and  Simond)  in  some  instances  at  least.® 
Piag-ue  ^-^^^  conditions  in  plague  are  peculiar  in  that  the 
disease  runs  an  acute  course  in  both  the  animal 
hosts  (rats  and  man)  and  in  the  insect  trans- 
mitter (flea).  Eats  do  indeed  suffer  from  clironic 
plague  in  some  instances,  but  this  is  not  a  septi- 
cemic condition,  hence  it  affords  little  or  no  oppor- 
tunity for  the  infection  of  fleas. 

It  may  be  questioned  whether  the  presence  of 
plague  bacilli  in  the  stomach  and  intestines  of  the 
flea  constitutes  a  true  infection,  but  it  seems  justi- 
fiable to  take  this  view  of  the  condition,  since  the 
bacilli  apparently  proliferate  in  this  locality  for  a 
few  days  at  least  (Verjbitski).  Verjbitski  found 
that  fleas  will  transmit  plague  for  three  days  after 
their  infection,  the  Indian  plague  commission  for 
from  eight  to  twenty-one  days  depending  on  the 
temperature  at  which  the  insects  had  been  kept — 
for  twenty-one  days  at  75° -80°  F.,  for  eight  days 

6.  The  British  commission  also  appears  to  have  been  suc- 
cessful in  proving  this  hereditary  transmission,  although  the 
attempt  had  failed  in  the  hands  of  Reed,  Carrol  and  Agra- 
monte,  and  of  Rosenau  and  Goldberger.  I'ossibly  it  occurs  in 
only  a  small  percentage  of  the  insects. 


HEREDITY    OF   INSECT   INFECTION.  75 

at  90°  F.  These  findings  also  correspond  with  the 
bacteriologic  examination  of  the  intestinal  and 
stomach  contents.  Verjbitski^s  work  in  relation 
to  the  bedbug  and  plague  was  referred  to  above. 

Although  plague  is  acute  in  both  the  animal 
and  insect  hosts,  maintenance  is  facilitated 
through  the  large  numbers  of  both  hosts  which 
are  present  in  plague  centers.  The  conditions 
render  possible  a  more  or  less  permanent  source 
of  infection  for  the  fleas  through  the  continued 
infection  of  fresh  rats.  The  possibility  also  exists 
that  the  chronic  nodular  plague  of  rats  may  be 
subject  to  exacerbations,  accompanied  by  septi- 
cemic infection,  a  condition  which  would  afford 
opportunity  for  the  further  infection  of  fleas.  It 
has  recently  been  shown  by  the  work  of  Wherry 
and  others  that  the  California  ground-squirrels 
have  played  a  part  in  the  persistence  of  plague  in 
that  region,  a  discovery  which  may  have  profound 
epidemiologic  importance  for  the  United  States. 

Inheritance  in  the  insect  has  been  mentioned  as 
a  factor  in  the  maintenance  of  Texas  fever,  Af- 
rican tick  fever  of  man,  yellow  fever  and  Eocky 
Mountain  spotted  fever.  Schaudinn  also  found 
that  the  mosquitoes  which  carry  Trypanosoma  noc- 
tuce  (the  "halteridium^'  of  the  stone  owl)  pass  the 
micro-organisms  to  the  next  generation  through 
the  eggs.  In  Texas  fever  this  appears  virtually  to 
be  the  sine  qua  non  for  maintenance  in  view  of  the 
peculiar  habit  of  the  tick  of  going  through  its  vari- 
ous stages  of  development  on  the  host  to  which 
the  larvse  first  become  attached."^    In  order  to  make 

7.  Most  ticks  pass  through  three  active  stages  in  their 
development.  The  freshly  engorged  and  impregnated  female, 
after  a  period  of  rest,  lays  a  great  many  eggs.  Following 
an  incubation  period  6-legged  larvae  emerge  from  the  eggs,  and 


76  INFECTION    AND    IMMUNITY. 

this  point  clear,  let  us  assume  that  the  disease  is 
not  hereditary  in  the  tick.  Let  some  normal  larvae 
become  attached  to  an  infected  steer.  They  might 
acquire  the  disease  from  this  animal,  but  could 
play  no  part  in  the  infection  of  others,  since  they 
do  not  abandon  this  host  until  they  have  reached 
the  adult  stage  and  the  females  are  prepared  to 

immnnity.  lay  eggs.  The  latter  then  drop  and  lay  their  eggs, 
and,  in  accordance  with  our  assumption,  the  larvge 
which  emerge  would  not  have  the  power  of  infect- 
ing further  animals.  In  this  case  the  tick  would 
be  a  factor  in  maintenance  only  in  the  event  that 
infected  individuals  should  through  accident  be- 
come dislodged  from  one  host  and  subsequently 
become  attached  to  a  susceptible  animal.  This 
may  occur  in  some  instances. 

East  Coast  The  Conditions  are  different  in  the  case  of 
another  piroplasmosis  of  cattle,  namely,  the 
Rhodesian  or  East  Coast  fever,  which  occurs  in 
Africa.  In  this  case,  as  determined  by  Lounsbury 
and  by  Theiler,  the  brood  from  an  infected  female 
is  not  infective,  but  lan^a^,  when  fed  on  diseased 
blood,  are  infective  after  reaching  the  nymphal 
stage,  and,  likewise,  when  infected  as  nymphs  the 
adults  have  the  power  of  transmission  (Rhipi- 
cephalus  appendiculatus) .  This  is  known  as  stage- 
to-stage  infection,  and  is  important  in  this  in- 
stance, inasmuch  as  the  larvae  and  nymphs  leave 
the  hosts  to  molt.     Following  the  molt  they  fre- 

soon  become  attached  to  hosts.  Then  they  feed,  pass  into  a 
quiescent  stage,  and  leaving  a  white  skin,  appear  as  8-Iegged 
nymphs.  These  also  feed,  become  quiescent  for  a  period,  and 
casting  off  a  white  skin  are  now  adults,  which  are  differ- 
entiated sexually.  In  some  instances,  as  in  the  tick  trans- 
mitting Texas  fever,  both  molts  occur  on  the  host.  More  fre- 
quently, howevbr,  other  species  leave  the  host  to  molt.  From 
several  weeks  to  several  months  are  required  for  the  whole 
cycle. 


Fever. 


INHERITANCE    OF   PIROPLASMAS.  77 

quently  reach  susceptible  hosts,  and  thus  keep  the 
disease  alive.  Koch,  perhaps  in  dealing  with 
another  species  of  tick  (Rhipicephakis  decolora- 
tus),  found  that  hereditary  transmission  of 
Ehodesian  fever  does  occur. 

Piroplasmosis  of  the  dog  presents  still  another 
interesting  condition  in  regard  to  inheritance  in 
the  tick.  Neither  the  larvas  nor  the  nymphs  of 
an  infected  female  are  able  to  produce  the  disease, 
but  when  they  reach  the  adult  stage  they  become 
infective.  It  has  been  assumed  that  the  period 
between  the  Qgg  and  the  adult  stage  is  required  by 
the  micro-organism  for  the  completion  of  its  sex- 
ual evolution,  the  latter  being  necessary  before  it 
could  again  become  infective.^  This  tick  also  leaves 
its  host  to  molt,  hence  the  adults  are  able  to  infect 
new  hosts,  and  from  the  latter  fresh  ticks  may 
again  become  infected.  The  disease  is  frequently 
chronic  in  the  dog  as  well  as  in  the  tick.  Motas 
found  that  the  tick  Rhipicephalus  bursa,  behaves 
in  a  similar  way  in  the  transmission  of  piroplas- 
mosis of  sheep.  In  this  instance  the  tick  remains 
on  the  host  for  the  first  molt,  but  leaves  it  for  the 
second.  An  infected  brood  is  able  to  transmit  the 
disease  only  after  it  reaches  the  adult  stage. 

Christophers  has  reported  still  another  variation 
in  the  inheritance  of  piroplasmas,  in  the  case  of 
Piroplasma  cams  in  India.  The  tick  concerned  in 
this  instance  was  Rhipicephalus  sanguineus,  which 
leaves  its  host  for  both  molts.  The  larvse  of  an 
infected  brood  are  not  virulent,  but  become  so 
when  they  reach  the  nymphal  and  adult  stages. 

8.  Experiments  by  Lounsbury  with  the  tick,  Hwmaphjf- 
salis  leacM. 


78  INFECTION    AND    IMMUNITY. 

Eocky  Mountain  spotted  fever  not  only  is  inher- 
ited in  the  tick,  but  both  larvae  and  nymphs  may 
acquire  the  disease  by  feeding  on  infected  blood 
and  transmit  it  by  biting  when  they  reach  the  sub- 
sequent stage.  Hence  both  hereditary  infection 
and  stage  to  stage  infection  occur  in  this  case. 

It  is  questionable  whether  any  disease  can  be 
maintained  in  an  insect  indefinitely  through  inher- 
itance alone.  Mollers^  found  that  South  African 
tick  fever  could  be  carried  into  the  third  genera- 
tion of  ticks  (Ornitliodoros  moubata),  neither  the 
second  nor  third  generation  of  ticks  having  had 
opportunity  to  suck  diseased  blood  in  the  mean- 
time. The  experiment  was  not  carried  beyond  this 
point.  In  relation  to  Eocky  Mountain  spotted 
fever  not  more  than  50  per  cent,  of  the  infected 
females  transmit  the  infection  to  their  offspring, 
hence  maintenance  through  inheritance  alone  is 
considered  as  impossible. 

Certain  considerations  relative  to  the  course  of 
infection  in  insects,  the  incubation  period  which 
may  intervene  between  the  moment  of  their  inocu- 
lation and  the  appearance  of  infectivity,  and,  in 
addition,  the  duration  of  their  infectivity,  are  of 
interest   and   importance.     These  points   may  be 
discussed  briefly  and  only  in  a  general  way. 
Innocuous-       It  is   striking   that   diseases   which   are   trans- 
sa*se*Ge?ms  mittcd  by  insects  appear  to  have  little  pathogenic 
carrie^^!  influence  on  the  insects  themselves.    The  malarial 
Plasmodia  penetrate  the  wall  of  the  stomach,  reach 
the  body  cavity  and  eventually  the  salivary  glands, 
and  this,   it  would   seem,  without  compromising 
seriously  the  health  of  the  mosquito.     The  flea 

9.  Ztschr.  f.  Hygiene,  1907,  Iviii,  277. 


PERIODS   OF  INFECTIVITY.  79 

harbors  in  its  alimentary  tract  for  several  clays 
or  weeks  the  most  virulent  plague  bacilli,  but 
eventually  they  are  cleared  away.  In  those  in- 
stances in  which  hereditary  transmission  occurs, 
as  in  piroplasmosis,  South  African  tick  fever,  and 
Eocky  Mountain  spotted  fever,  the  eggs  may  con- 
tain large  numbers  of  the  specific  micro-organisms 
and  yet  give  rise  to  apparently  healthy  larvae, 
which  are  able  to  pass  through  the  successive 
stages  into  the  adult  form,  still  retaining  the  viru- 
lent micro-organisms  in  their  organs  and  cells.  It 
is  probably  by  virtue  of  this  bland  relationship 
that  insects  are  able  to  figure  as  the  carriers  of 
infection.  If  the  latter  were  more  virulent  for 
the  insect  hosts  it  is  fair  to  assume  that  their 
death  in  large  numbers  would  minimize  their  role 
as  inoculators  of  other  animals. 

In  the  case  of  the  flea  and  plague,  the  insect 
is  infective  immediately  or  soon  after  it  has  in- 
gested blood,  but  the  period  of  infectivity  is  lim- 
ited to  a  few  days  (Yerjbitski)  or  at  the  most  a 
few  weeks  (the  Indian  Plague  Commission).  This 
has  been  referred  to  above  as  acute  infection  of 
the  insect.  Mechanical  transmisssion  is  a  term 
which  has  been  used  to  signify  the  pure  mechan- 
ical conveyance  of  micro-organisms  by  an  insect 
from  a  diseased  to  a  healthy  animal.    The  role  of  Periods  of 

^  '^  1-1  Infectivity. 

the  flea  in  carrying  plague  may  be  simply  a  me- 
chanical one,  particularly  when  it  transfers  the 
disease  immediately  after  its  infection.  But,  inas- 
much as  proliferation  of  the  bacillus  seems  to 
occur  in  the  flea,  and  since  his  infectivity  may  last 
for  three  weeks  or  more,  proliferation  may  be  re- 
sponsible for  the  later  infectivity.  In  this  event 
the  transmission  depends  on  biological  as  well  as 


so  IXFECTIOy    AXD    IMMUNITY. 

Meciianu;^^  meclianical  factors.  Transmission  of  this  type 
Tranimi*sliSm  pi'obablv  demands  a  high  degree  of  virulence  and 
infectivity  on  the  part  of  the  micro-organisms, 
necessitating  the  introduction  only  of  very  small 
numbers.  One  of  the  conclusions  of  Verjbitski  is 
that  "animals  could  not  be  infected  by  the  bites  of 
fleas  and  bugs  which  had  been  infected  by  animals 
whose  own  infection  had  been  occasioned  by  a  cul- 
ture of  small  virulence,  notwithstanding  the  fact 
that  the  insects  may  be  found  to  contain  abundant 
plague  microbes."^*^ 

Another  condition  is  represented  in  Rocky 
Mountain  spotted  fever,  in  which  the  insects  are 
infective  not  only  immediately  or  soon  after  suck- 
ing diseased  blood,  but  also  for  an  indefinite  sub- 
sequent period.  In  this  instance  the  tick  under- 
goes generalized  infection,  as  previously  men- 
tioned. It  is  possible  that  the  conveyance  which 
takes  place  immediately  after  infection  is  of  the 
mechanical  type,  but  this  cannot  be  true  of  the 
later  transmissions,  nor  of  those  by  the  members 
of  the  following  generation.  In  the  latter  we  have 
to  do  with  biological  transmission,  which  in  these 
two  cases  depends  on  proliferation  of  the  micro- 
organisms and  a  general  invasion  of  the  tissues  of 
the  insects.  The  term  "biological  transmission" 
was  originally  applied  to  those  cases  in  which  the 
micro-organisms  (protozoan)  undergo  a  compli- 
cated sexual  cycle  of  development  in  the  insect,  as 
in  malaria,  but  the  principle  remains  the  same 
with  the  bacterial  diseases,  although  the  method 
of  proliferation  is  a  simple  one,  consisting  merely 
of  fission. 


10.     Jour.  Hygiene,  1908,  viii,  205. 


I^CUBATWN    IN    INSECTS.  81 

When  the  mosquitoes  of  malaria  and  yellow  incui>ation 
fever  suck  diseased  blood  a  definite  incubation  insects. 
period  must  elajDse  before  they  are  able  to  convey 
infection  to  other  individuals  by  their  bites.  Fol- 
lowing the  ingestion  of  malarial  blood  by  the  mos- 
quito (various  species  of  Anopheles) ,  the  parasite 
undergoes  a  sexual  type  of  proliferation  in  the  in- 
sect^s  stomach,  the  product  of  which,  the  sickle- 
shaped  bodies,  reach  the  salivary  glands  only  after 
eight  or  ten  days.  These  are  the  pathogenic  forms 
of  the  parasite  which  are  inoculated  into  man  by 
the  mosquito.  In  the  intermediate  stages  of  this 
C3^cle  the  parasite  is  not  infective.  The  mosquito 
(Stegomyia)  which  transmits  yellow  fever  is  not 
infective  until  at  least  twelve  days  after  it  has 
sucked  diseased  blood.  And  it  now  appears  also 
that  a  similar  incubation  period  occurs  in  the 
tsetse  fly  in  its  role  as  the  carrier  of  sleeping-sick- 
ness. After  the  insects  are  once  infected,  however, 
they  continue  virulent  for  a  long  time.  Hence  a 
primary  non-infective  stage  is  succeeded  by  a  pro- 
longed infective  stage  in  this  type  of  transmission. 

On  the  basis  of  the  conditions  in  malaria  the 
temptation  has  been  a  strong  one  to  conclude  that 
a  primary  non-infective  stage — incubation  period 
— in  the  insect  carrier  is  indicative  of  a  sexual 
cycle  in  the  development  of  the  parasite;  hence 
also  of  the  protozoan  character  of  the  parasite. 
Thus  it  is  anticipated  in  many  quarters  that  the 
micro-organism  of  yellow  fever,  at  present  un- 
known, will  prove  to  be  a  protozoan,  because  of 
the  incubation  period  in  the  mosquito,  mentioned 
above.  Novy,  however,  has  very  aptly  pointed  out 
that  an  incubation  period  in  the  insect  might  well 
occur  in  the  case  of  a  bacterial  disease  as  well  as 


82  I^^FEGTIO^'    A\D    IMMUNITY. 

in  a  protozoon.^^     Given  a  case  in  which,  the  dis- 

Transmission  ease  is  causcd  bv  a  bacterium  rather  than  a  proto- 

of  Bacteria.    ^^^^^  ^^^^  ^^^  assumc,  first,  that  the  infection  in 

the  insect  is  limited  to  its  alimentary  tract;  or, 
second,  that  a  generalized  infection  of  the  carrier 
takes  place  with  a  localization  of  the  micro-organ- 
isms in  its  salivary  glands.  In  the  first  instance 
a  large  proportion  of  the  organisms  ingested  with 
the  infected  blood  reach  the  stomach  and  intes- 
tines, whereas  it  is  probable  that  a  relatively  small 
number  remain  in  the  proboscis.  "When  the  insect 
feeds  at  once,  or  soon,  on  another  (healthy)  ani- 
mal the  number  of  micro-organisms  injected  from 
the  proboscis  may  be  insufficient  to  infect  the  new 
host.  Some  days  might  be  required  for  prolifera- 
tion to  result  in  an  infective  quantity,  either  in 
the  proboscis,  stomach,  intestines,  or  by  contiguous 
extension,  in  the  salivary  ducts  and  glands.  At 
the  time  of  inoculation  the  micro-organisms  might 
simply  be  washed  from  the  proboscis  into  the  cutis 
by  means  of  the  salivary  secretion,  or  directly  in 
the  latter,  or  "after  a  certain  amount  of  regurgita- 
tion from  the  stomach  had  taken  place  into  the 
proboscis. 

In  the  second  case,  in  Avhich  the  insect  under- 
goes a  generalized  infection,  the  primary  non-in- 
fective period  (incubation  period)  may  well  rep- 
resent the  time  required  for  this  general  invasion, 
with  the  consequent  localization  of  the  bacteria 
in  the  salivary  glands.  We  have  a  very  good 
analogy  in  typhoid  fever  in  man,  in  which  a  very 
definite  incubation  period  precedes  generalized 
infection. 


11.  The  Role  of  Protozoa  in  Pathology;  Proc.  of  the  Path. 
Soc.  of  Philadelphia,  1907,  pp.  1-27. 


Trn  n  sin  i  »i)  si  o  i> . 


MODE   OF   INSECT   TRANSMISSION.  83 

Hence  it  seems  possible  that  errors  may  result 
in  assuming  that  a  primary  non-infective  period 
in  the  insect  points,  in  an  obligate  manner,  to  the 
protozoan  nature  of  a  parasite. 

So  far  we  have  considered  three  types  of  trans-  Types  of 
mission  by  insects;  the  first,  in  which  the  insect  is 
infective  immediately  or  soon  after  ingesting  dis- 
eased blood  but  not  for  a  prolonged  period  (the 
flea  in  plague)  ;  the  second,  in  which  the  carrier 
is  infective  almost  immediately  and  for  a  prolonged 
period  later  (ticks  in  Eocky  Mountain  spotted 
fever)  ;  third,  in  which  a  harmless  incubation 
period  is  followed  by  a  prolonged  virulent  period 
(malaria  and  yellow  fever). 

A  fourth  possibility,  which  is  perhaps  not  yet 
thoroughly  established,  is  that  of  an  immediate 
infective  period,  followed  by  a  non-infective,  fol- 
lowed again  by  an  infective.  The  conditions  as  as- 
certained so  far  indicate  that  this  may  be  the  case 
in  the  transmission  of  trypanosomes  by  tsetse  flies. 
Until  latel}^  it  was  the  experience  that  the  flies 
could  convey  nagana  only  for  one  or  two  days 
after  their  feed  on  infected  blood.  Lately,  how- 
ever, Ivleine^^  has  found  that  an  incubation  period 
of  about  twenty  days,  or  a  little  less,  occurs  in  the 
fly,  and  from  then  on,  even  up  to  eighty-three 
days  (Taute),  it  is  able  to  transmit  infection. 
This  work  has  been  done  with  the  flies,  Glossina 
morsitans  and  G.  palpalis,  in  connection  with  the 
trypanosomes  of  nagana  (T.  irucei),  and  sleeping 
sickness  (T.  gamhiense).  The  results  have  been 
corroborated  by  Bruce.  The  first  stage  of  infec- 
tivity  of  the  flies  then  remains  for  explanation. 

12.  Deutsche  med.  Wchnschr.,  March  18,  May  27  and  July 
22,  1909. 


84  INFECTION    AND    IMMUNITY. 

It  is  possible  that  this  is  purely  a  mechanical  trans- 
mission. In  many  of  the  experiments  rather  large 
numbers  of  flies  have  been  used  on  a  single  animal, 
and  in  this  case  an  infective  quantity  of  the  para- 
sites might  well  be  introduced  mechanically,  where- 
as a  single  fly  might  be  able  to  produce  infection 
only  after  the  parasite  had  multiplied  in  its  tis- 
sues, and,  perhaps,  had  reached  the  salivary  glands. 
It  is  well  known  that  an  intermediate  "insect 
stage"  of  the  trypanosome  is  not  required  for  infec- 
tivity,  as  appears  to  be  the  case  with  malaria. 
Trypanosomatic  diseases  may  be  carried  directly 
from  one  animal  to  another  by  the  injection  of 
blood  for  an  indefinite  period.  A  sexual  stage  of 
the  trypanosome  has  not  yet  been  shown  to  occur 
in  the  tsetse  fly. 
uniqne  Type  A  uuiquc  type  of  iuscct  transmission  was  de- 
TransmiV^ion*.  scribcd  recently  by  Miller^^  in  the  case  of  a  dis- 
ease of  rats  which  is  caused  by  a  protozoan  organ- 
ism, Hepatozoon  perniciosum,  a  new  genus  as  well 
as  a  new  species.  The  transmitter  is  a  mite, 
Lelaps  ecliidninus.  The  latter  derives  its  infection 
by  sucking  the  blood  of  diseased  rats,  in  which  the 
micro-organisms,  at  a  particular  stage  of  their 
development,  occur  within  large  mononuclear  leu- 
cocytes. A  sexual  phase  of  the  parasite  takes  place 
in  the  stomach  of  the  mite,  forming  an  ookinet. 
The  latter  penetrates  the  stomach  wall,  reaches  the 
body  cavity  of  the  mite,  and  becomes  encysted 
(oocyst  stage).  Within  the  cyst  the  parasite  sub- 
divides to  form  a  number  of  sporoblasts,  each  of 
which  eventually  contains  from  fourteen  to  twenty 
sporozoites.     Miller  readily  produced  the  disease 

13.  Bull.  No.  46,  Hygienic  Laboratory,  U.  S.  Public  Health 
and  Marine-Hospital  Service,  Washington,  D.  C. 


INSECT  AND   MULTICELLULAR   PARASITES.  85 

in  many  rats  by  feeding  them  bread  which  had 
been  mixed  with  crushed  infected  mites.  The  in- 
testinal juices  of  the  rat  break  up  the  sporocyst. 
and  set  free  the  sporozoites,  wliich  as  "vermicules" 
penetrate  to  the  veins  and  lymphatics  and  reach 
the  liver,  where  they  undergo  an  asexual  prolifera- 
tion within  liver  cells.  From  these  the  young 
merozoites  are  liberated  and  reach  the  general  cir- 
culation, again  as  vermicules.  It  is  the  last  stage 
which  is  taken  up  afresh  by  the  mites.  x\lthough 
the  sporocysts  may  occur  in  the  salivary  glands  of 
the  mite  as  well  as  in  other  parts  of  the  body,  Mil- 
ler found  no  reason  to  believe  that  the  parasite  is 
inoculated  into  the  rat  by  the  bite  of  the  mite. 
The  latter  feeds  only  at  night,  leaving  the  host 
in  the  day.  and  at  a  subsequent  feed  may  well 
reach  a  healthy  rat,  which  in  turn  becomes  in- 
fected by  eating  a  sufficient  number  of  the  mites. 
Miller  reproduced  the  infection  also  by  this  "nat- 
ura?^  method.  Other  modes  of  infection,  artificial 
in  character,  proved  to  be  unsuccessful. 

That  insects  may  have  a  relation  to  the  main-  insects  and 
tenance  and  extension  of  some  diseases  caused  by  ParaVites?  * 
multicellular  parasites  is  illustrated  by  the  trop- 
ical and  subtropical  disease  of  filariasis,  of  which 
elephantiasis  is  one  of  the  most  pronounced  clin- 
ical symptoms.     The  larval  worms  often  exist  in 
large  numbers  in  the  blood  of  man,  particularly 
at  night.     AYhen  certain  mosquitoes  suck  infected 
blood  at  this  time  one  or  more  of  the  worms  is 
ingested,  undergo  further  development,  and  eventu-         T 
ally  here  through  the  stomach  wall  and  reach  the 
breast  muscles  of  the  insect.     The  exact  manner 
in  Avhich  the  parasites  are  reinoculated  into  man 
is  unknown.     It  was   supposed  by   Manson  that 


86  lyFECTION    AND    IMMUNITY. 

many  of  the  female  mosquitoes  die  in  the  water 
after  they  have  laid  their  eggs  and  that  the  water 
thus  becomes  contaminated  with  the  filaria.  The 
use  of  such  water  results  in  the  infection  of  man 
through  his  intestinal  tract.  Suspicion  falls  on 
several  species  of  mosquitoes :  Culex  pipiens,  C. 
ciliaris,  C.  faiigans;  Anopheles  cosialis,  A.  rossi_, 
A.  maculipennis. 

A  number  of  worms  which  are  parasitic  in  one 
animal  or  another  are  derived  from  insects,  the 
latter  serving  as  hosts  for  the  larval  stages.  Infec- 
tion of  the  digestive  canal  originates  after  eating 
the  insects  (See  Nuttall,  Hygienische  Eundschau, 
1899,  ix,  505). 
Specificity  in  There  is  a  certain  degree  of  specificity  in  the 
Transmission,  transmission  of  a  disease  by  an  insect,  but  this  is 
by  no  means  absolute.  In  yellow  fever  it  appears 
to  be  very  strong,  inasmuch  as  only  one  species  of 
mosquito  appears  to  be  capable  of  carrying  the 
disease  (Stegomyia  fasciata).  An  opposite  ex- 
treme is  found  in  the  case  of  malaria,  in  which  at 
least  twenty-five  different  species  of  Anopheles 
have  been  shown  to  be  capable  of  either  natural  or 
experimental  transmission.^*  Several  species  of 
ticks  are  able  to  carry  Texas  fever  and  probably 
other  piroplasmoses  of  cattle.  At  least  two  spe- 
cies of  ticks  carry  Eocky  Mountain  spotted  fever 
(Dermncentor  venustus,  Banks,  and  D.  modesfiis. 
Banks).  Two  species  of  tsetse  flies  may  carry  the 
parasites  of  either  nagana  or  sleeping-sickness. 
The  carrying  power,  however,  is  usually  limited 
,  to  different  species  under  a  common  genus.     As  far 

as   observations  have  gone  only  Anopheles   carry 

14.   Huge :     Kolle    and    Wassermann's    Handbuch    d.    path. 
Mikioorg. 


SPECIFICITY    IN    TRANSMISSION.  87 

malaria,  only  Glossina  flies  appear  to  transmit  na- 
gana  and  sleeping  sickness,  and  only  Dermacentor 
ticks  carry  Eocky  Mountain  spotted  fever.  An 
exception  is  found  to  this  in  the  case  of  a  spiril- 
losis  of  fowls  in  South  America.  Naturally  this 
disease  is  transmitted  by  a  species  of  tick,  Argas 
mimatus,  but  experimentally  it  may  also  be  trans- 
mitted by  Ornithodorus  moubata.  The  lattei",  in 
addition  to  transmitting  the  disease  just  men- 
tioned, may  also  carry  the  European  relapsing 
fever,  and  is  habitually  concerned  in  the  convey- 
ance of  the  South  African  tick  fever  of  man.  . 


CHAPTER  VII. 


Patlio- 

genicity, 

Virnlence. 


SPECIAL  FEATURES  OF  INFECTION.  ^ 

(1)    Virulence,  Toxicity,  Etc. 

The  word  pathogenicity,  in  its  relation  to  infec- 
tion, refers  to  the  power  of  an  organism  to  produce 
disease,  and  often  to  the  character  of  the  changes 
which  it  causes.  Virulence  in  all  essential  respects 
is  synonymous  with  pathogenicity,  but  is  used 
more  commonly  in  describing  the  degree  of  path- 
ogenic power  which  a  micro-organism  posseses. 
Thus  virulent  and  avirulent  (or  non-virulent) 
strains  of  the  cholera  vibrio  or  diphtheria  bacillus 
are  spoken  of. 
Toxicity.  Toxicity  refers  to  the  poisonous  properties  of  a 
microbe  or  its  secretions.  As  a  property  it  is  not 
necessarily  associated  with  the  living  micro-organ- 
isms. The  question  is  still  discussed  as  to  whether 
toxicity  and  virulence  are  coextensive,  even  if  they 
are  not  identical  properties.  Undoubtedly,  toxicity 
is  one  of  the  factors  on  which  virulence  depends, 
and.  from  the  standpoint  of  the  micro-organism,  it 
may  be  the  sole  property.  Some  organisms  of  little 
or  no  pathogenic  or  infective  power  nevertheless 
possess  a  protoplasm  which  is  more  or  less  poison- 
ous, as  certain  aspergilli,  penicillia  or  Bacillus 
suhtilis. 

Infectivity,  or  infectiousness,  relates  to  the 
power  of  a  micro-organism  to  maintain  itself  and 
to  multiply  in  a  living  host.    One  which  is  able  to 


Infectivity. 


SPECIALIZATION    IN    VIRULENCE.  89 

obtain  a  foothold  and  to  produce  disease,  even 
when  a  very  minute  qnantit}'  has  been  introduced; 
or  one  which,  after  introduction,  is  able  to  prolifer- 
ate to  an  enormous  degree  in  a  particular  host  is 
said  to  be  very  infective,  or  infectious,  for  this  host. 

Infectivity  is  not  synonymous,  nor  is  it  neces- 
sarily coextensive,  with  virulence  or  pathogenicity. 
Thus  Trypanosoma  leiuisi  for  the  rat,  the  ma- 
larial parasites  for  the  mosquito,  and  the  virus  of 
Rocky  Mountain  spotted  fever  for  the  tick  are 
highly  infective,  but  have  a  very  low  grade  of  path- 
ogenicity for  these  hosts.  The  leprosy  bacillus,  the 
spirochete  of  syphilis,  and  the  tubercle  bacillus 
have  marked  infectivity  for  man,  but  their  viru- 
lence, as  indicated  by  the  slow  progressive  character 
of  the  diseases,  may  be  considered  as  moderate, 
although  the  final  event  may  be  tragic  enough.  On 
the  other  hand,  certain  organisms  possess  great 
infectivity  and  great  virulence  at  the  same  time, 
as  plague,  anthrax  and  the  glanders  bacilli  (acute 
glanders)  for  man,  and  the  tr3^panosomes  of  sleep- 
ing sickness,  nagana  and  dourine  for  white  mice. 

The  virulence  of  some  micro-organisms  is  often  speciaiiza- 
specialized  with  regard  to  particular  species  of  ani-  vfAience. 
mals.  Thus  measles,  scarlet  fever  and  leprosy  seem 
to  attack  man  only,  and  no  animal  can  be  infected 
with  their  viruses.  Smallpox  and  syphilis  are  less 
specialized.  Smallpox  can  be  inoculated  into  the 
ox  and  to  a  certain  degree  into  the  rabbit,  and  syph- 
ilis into  monkeys,  and  perhaps  also  into  the  rabbit, 
although  the  latter  may  not  yet  be  definitely  deter- 
mined. Malaria  and  yellow  fever  infect  only  man 
and  the  mosquitoes  which  carry  these  diseases. 
Many  other  pathogenic  organisms  are  in  contrast  to 
those  mentioned,  in  that  they  are   able  to  cause 


90  II^FEGTWS    A^D    IMMUNITY. 

• 
disease  in  a  wide  range  of  animals.  Such  microbes 
are  the  p3'0genic  cocci,  the  bacilli  of  tuberculosis, 
glanders,  typhoid  fever,  cholera,  paratj^phoid  fever, 
tetanus,  diphtheria,  plague,  certain  of  the  tr3^pano- 
somes,  and  many  others.  There  are  examples  of 
immunity,  however,  even  to  these  micro-organisms 
of  rather  general  virulence,  such  as  that  of  the  alli- 
gator and  the  fowl  to  tetanus,  and  of  the  rat  to 
diphtheria. 

In  contrast  to  the  examples  mentioned  above, 
are  the  non-pathogenic  parasites,  which  experi- 
mentation has  shown  to  have  no,  or  insignificant 
virulence  for  any  animal  whatsoever.  B.  suhtilis 
and  B.  megatherium  are  cited  as  representing  such 
organisms.  The  former,  however,  is  not  absolutely 
without  pathogenic  power,  since  it  has  been  observed 
as  the  cause  of  panophthalmitis  in  a  number  of 
cases,  and  by  previously  lowering  intraperitoneal 
resistance  (by  the  injection  of  "aggressins")  Weil 
caused  fatal  peritonitis  in  guinea-pigs  with  this 
organism. 

Standing  somewhat  above  these  more  or  less 
harmless  microbes  in  pathogenic  power  are  the  so- 
called  acid-fast  grass  bacilli  and  similar  organisms, 
which  are  able  to  produce  only  slight  local  changes 
in  animals,  and  which  are  soon  destroyed  by  the 
antibacterial  agencies  of  the  host. 
Variations.  Virulencc  is  a  variable  factor  even  with  regard 
to  different  strains  of  a  given  mioro-organism. 
Diphtheria  bacilli  cultivated  from  various  cases 
show  a  rather  wide  range  of  virulence,  and  similar 
observations  have  been  made  with  regard  to  typhoid 
bacilli,  streptococci,  pneumococci,  tubercle  bacilli, 
plague  bacilli  and  other  organisms.  With  few  ex- 
ceptions, pathogenic  micro-organisms  tend  to  lose 


PASSAGE   THROUGH  ANIMALS.  91 

virulence  when  they  are  cultivated  for  any  length 
of  time  on  the  ordinary  culture  media. 

A  common  device  for  the  maintenance  or  increase  Passage. 
of  virulence  is  that  of  passage  through  some  suit- 
able animal.  The  process  consists  of  the  inocula- 
tion of  the  animal  with  a  pure  culture,  permitting 
the  infection  to  run  its  course  or  to  proceed  for  a 
number  of  days,  and  at  this  time  recovering  the 
micro-organism  on  culture  media  from  the  tissues 
of  the  animal.  Eoux  and  Metchnikoff  modified  this 
technic  by  placing  a  culture  of  the  organism  in  a 
sealed  collodion  sac,  which  is  then  imbedded  in  the 
peritoneal  cavity  of  a  living  animal.  After  a  suffi- 
cient length  of  time  the  sac  is  removed  and  the 
process  repeated.  By  repeating  the  passage  at  suit- 
able intervals  virulence  may  be  maintained  at  a 
rather  constant  high  point  (cholera  vibrio,  strepto- 
cocci, etc.).  An  effective  substitute  for  passage  is 
sometimes  found  in  the  use  of  a  culture  medium, 
which  in  its  constitution  approximates  that  of  the 
tissues  of  an  animal.  Thus  the  virulence  of  pneu- 
mococci  and  streptococci  is  retained  by  cultivation 
on  blood  agar  or  in  rabbit  or  human  serum  or  in 
ascitic  fluid. 

Animal  passage  increases  virulence  in  the  most 
marked  manner  for  the  species  of  animal  which  is 
used  in  the  experiment,  although  some  increase  is 
usually  manifested  toward  other  susceptible  species. 
In  a  number  of  instances  passage  through  one  ani- 
mal results  in  a  decrease  of  virulence  for  one 
species  and  an  increase  for  another.  Thus  Pasteur 
found  that  passage  of  the  virus  of  swine  erysipelas 
(ScJiiueinerotlauf)  through  pigeons  increased 
virulence  for  the  swine,  but  it  was  decreased  for 
this  animal  when  passed  from  rabbit  to  rabbit. 


!)2  lyFECTIOy    AXD    IMMUNITY. 

The  virus  of  h3^drophobia,  when  passed  through 
several  consec-utive  rabbits,  and  that  of  smallpox 
when  passed  through  the  calf,  lose  in  virulence  for 
man. 
Effect  of  The  increase  of  virulence  which  results  from 
passage  has  been  explained  by  assuming  that  all 
the  weaker  and  less  virulent  individuals  of  the 
culture  are  killed  by  the  serum  and  leucoc3^tes  of 
the  animal,  leaving  the  more  resistant  and  more 
virulent.  This  process  of  selection  is  nrobably  an 
important  factor  in  the  change,  but  it  would  hardly 
explain  the  increase  which  occurs  when  an  organism 
is  grown  on  heated  serum.  It  seems  probable,  as 
suggested  by  Eisenberg  and  others,  that  as  a  conse- 
quence of  residence  in  the  body  of  the  animal  the 
culture  becomes  immunized  against  the  antibac- 
terial factors  (bactericidal  amboceptors  and  opson- 
ins) of  the  host,  which  would  naturally  render  the 
organism  a  more  dangerous  one  for  subsequent 
animals  into  which  it  may  be  injected.  It  is  even 
possible,  as  suggested  by  Welch  and  others,  that 
certain  elements  in  the  body  fluids  may  stimulate 
the  micro-organisms  to  a  more  abundant  secretion 
of  toxins  and  other  substances  (amboceptors),  and 
that  the  increased  virulence  caused  by  passage  may 
depend  on  the  retention  of  this  power  after  leaving 
the  tissues  of  the  host. 

It  is  probable  that  all  organisms  which  are  able 
to  live  for  a  shorter  or  longer  time  within  the  tis- 
sues of  an  animal  cause  anatomic  changes  and 
abnormal  symptoms  sooner  or  later.  This,  of  course, 
does  not  apply  to  those  which  live  habitually  on  the 
cutaneous  or  mucous  surfaces.  Those  which  live 
on  the  skin  do  not  reach  the  interior  because  of 
mechanical  obstacles,  and  regarding  those  which 


DOSAGE   OF   MICRO-ORGANISMS.  US 

inhabit  the  mucous  surfaces  constantly,  it  would 
seem  that  an  adaptation  has  taken  place  between 
such  surfaces  and  the  micro-organisms,  so  that  the 
latter,  although  often  pathogenic,  are  not  able  to 
reach  deeper  tissues.  The  least  harmful  infection 
of  which  one  could  conceive  would  be  one  in  w^hich 
the  micro-organism  disturbed  the  host  in  no  way, 
except  in  so  far  as  it  used  a  certain  amount  of  its 
substance  for  nutrition.  This  would  be  a  case  of 
simple,  comparatively  harmless,  parasitism,  which 
in  man,  is  best  illustrated  by  the  organisms  which 
live  habitually  on  the  mucous  surfaces. 

It  is  possible  that  harmless  tissue  invasion  finds 
examples  in  some  of  the  insects,  although  this  may 
not  be  maintained  positively.  The  apparent  harm- 
lessness  of  the  organisms  of  malaria,  yellow  fever, 
South  African  tick  fever  and  Eocky  Mountain  spot- 
ted fever  for  the  insects  which  harbor  them,  was 
mentioned  in  the  preceding  chapter.  Certain  infec- 
tions do,  indeed,  run  a  very  chronic  and  benign 
course,  as  the  ordinary  trypanosomiasis  of  rats,  but 
they  are  not  without  discoverable,  or  even  fatal, 
effects  eventually. 

The  quantity  or  dosage  of  micro-organisms  re-  Dosag:e. 
quired  for  infection  depends  on  their  virulence 
and  the  degree  of  their  parasitic  power  (infectiv- 
ity)  ;  this  varies  with  different  species  and  also 
with  different  strains  of  the  same  organism.  The 
anthrax  bacillus  is  very  infective  and  may  reach  a 
high  degree  of  virulence,  so  that  a  single  organism 
has  been  known  to  produce  fatal  disease  in  experi- 
mental animals.  Extremely  minute  quantities  of 
some  of  the  more  virulent  trypanosomes  are 
required.  The  tubercle  bacillus,  even  when  most 
virulent,  is  hardly  so  infective;  it  is  said  that  eight 


94  INFECTION    AND    IMMUNITY. 

may  produce  infection  when  given  intraperito- 
neally  into  the  guinea-pig,  and  twent}^  to  thirty 
when  into  the  rabbit  (Wyssokowicz).  Many  hun- 
dreds of  the  most  virulent  cholera  vibrios  and 
typhoid  bacilli  are  required  to  produce  fatal  infec- 
tion in  the  guinea-pig.  In  contrast  to  the  condi- 
tions mentioned  are  various  saprophytic  organisms 
which,  regardless  of  the  quantity  introduced,  either 
do  not  produce  infection  at  all,,  or  do  so  only  after 
the  resistance  of  the  animal  has  been  lowered  arti- 
ficially. 

Among  those  who  are  equally  exposed  to  infec- 
tion in  an  epidemic  of  typhoid  fever,  the  escape  of 
many  probably  is  due  to  the  ingestion  of  a  small 
quantity  of  bacilli  which  is  insufficient  to  produce 
disease.  Individual  susceptibility,  and  temporary 
low  resistance,  are  other  factors. 

(2)   Types  of  Infection. 

There  are  wide  variations  in  the  physical  rela- 
tionships which  different  pathogenic  micro-organ- 
isms hold  to  the  tissues  of  the  body.  This  has 
already  been  suggested  in  the  discussion  of  infec- 
tion atria,  in  which  it  was  shown  that  certain 
organisms  have  a  specific  preference  for  points  of 
primary  invasion. 

This  tendency  of  a  specific  relationship  to  par- 
ticular tissues  is  kept  up  in  many  instances  after 
the  microbes  have  reached  the  interior  of  the  body. 
seitcUve  The  malarial  plasmodia  enter  and  destroy  the 
Di\^iibntrom  erythrocytes  and  cause  enlargement  of  the  spleen 
and  liver,  while  other  organs  are  affected  to  a 
much  less  degree  as  a  rule.  The  pneumococcus 
has  a  great  affinity  for  the  pulmonary  tissue  and 
for    endothelial    structures;    it    frequently    causes 


CUTANEOUS    IXFECTIONS.  95 

meningitis  and  is  present  in  the  blood  in  virtuall}' 
all  cases  of  pneumonia.  The  gonococcus,  aside 
from  its  predilection  for  the  urethra,  readily 
becomes  localized  in  the  joints,  and  occasionally  on 
the  valves  of  the  heart.  The  micro-organism  which 
causes  acute  articular  rheumatism  has  a  specific 
affinity  for  the  joints  and  endocardium.  It  would 
seem  that  the  virus  of  hydrophobia  attacks  the  cen- 
tral nervous  system  almost  to  the  exclusion  of 
other  tissues.  The  spirochete  of  syphilis,  although 
it  may  cause  changes  in  any  organ  of  the  body,  is 
particularly  prone  to  produce  proliferation  of  the 
vascular  endothelium  and  subendothelial  connect- 
ive tissue. 

The    fungi    which    cause    pityriasis    versicolor,   cutaneous 

"  .  I      J  -I      n  ^     Infections. 

ringworm,  barber^s  itch,  erythrasma  and  favus 
attack  only  the  cutaneous  surfaces.  Ringworm  in 
the  child  is  prone  to  be  limited  to  the  scalp,  whereas 
in  the  adult  it  occurs  more  commonly  on  the 
smooth  skin.  In  ringworm  and  pityriasis  versi- 
color only  the  superficial  skin  is  involved,  and  in  skin. 
the  former  the  hair  follicles  and  the  hairs.  In 
favus  and  barber's  itch  the  cutis  vera  is  often 
inA^aded,  and  in  the  former  healing  usually  takes 
place  with  scar  formation.  The  organisms  appar- 
ently never  become  generally  distributed  in  the 
body,  and  never,  or  rarely,  cause  symptoms  of  gen- 
eral intoxication. 

There  are  many  other  organisms  of  more  general 
pathogenic  powers  which  frequently  cause  infec- 
tions in  the  skin  and  other  superficial  tissues, 
although  they  have  no  specific  relationship  to  the 
skin.  They  are  found  now  in  one  tissue  and  now 
in  another,  and  may  in  fact  invade  any  organ  of 
the   body.      Such   organisms   are   the   streptococci 


9C  INFECTIOX    AXD    IMMUNITY. 

(er3'sipelas);  staphylococci  (acne,  furunculosis), 
the  bacillus  of  anthrax  (malignant  carbuncle),  the 
tubercle  bacillus  (lupus,  anatomic  tubercle),  blasto- 
mycetes,  and  others.  It  is  a  rather  peculiar 
feature  of  tuberculosis  and  blastomycosis  that, 
given  a  primary  infection  of  the  skin,  there  is  not 
a  marked  disposition  to  the  metastatic  invasion  of 
deeper  and  remote  tissues.  This  does  occur  occa- 
sionally, it  is  true,  but  it'  seems  that  a  primary 
localization  in  the  skin  has  a  tendency  to  immunize 
the  rest  of  the  bod}^  against  invasion  by  these 
organisms. 
Local       Diphtheria  and  tetanus,  as  stated  elsewhere,  rep- 

Infection    and  ^  tip-  p 

Soluble  resent  another  tvpe  of  local  infection,  the  former 

Toxins.     .  "  p  1       1     1  J        1      • 

involving  mucous  surfaces,  the  latter  being  a  wound 
infection.  In  these,  the  organisms  do  not  become 
generally  distributed  in  the  body,  or,  at  any  rate, 
not  to  a  marked  and  essential  degree,  but  the  gen- 
eral intoxication  results  from  the  action  of  specific 
soluble  toxins  which  are  absorbed  and  distributed 
through  the  body  by  the  circulation.  The  organ- 
isms are  largely  limited  to  the  point  of  primary 
invasion  or  implantation.  Their  toxins  may  be 
obtained  free  from  the  bacterial  cells  in  artificial 
culture  media,  and  such  toxins  when  injected  are 
able  to  cause  the  symptoms  of  the  disease. 
Intoxication  The  bacillus  of  botulism  belongs  to  the  same 
Infection,  group  as  the  tetanus  and  diphtheria  bacillus,  in 
that  it  produces  a  specific  soluble  toxin  in  culture 
~"  media  which  is  able  to  cause  the  symptoms  of  the 

disease.  The  mechanism  of  pathogenesis  is  differ- 
ent, however.  The  toxin  which  produces  the  dis- 
ease has  already  been  formed  in  the  diseased  meat 
by  the  bacillus  before  the  meat  is  eaten,  and  the 
poisoning  results  from  the  absorption  of  this  toxin 


CONTINUOUS   INVASION.  97 

through  the  wall  of  the  intestines.  The  bacillus 
itself  is  believed  not  to  proliferate  in  the  intes- 
tines. The  condition  is  one  of  intoxication  with- 
out true  infection. 

In  some  of  the  intestinal  diseases  the  cavity  of   continucms 

"^     .       Invasion 

the  intestines  appears  to  act  as  a  sort  of  reservoir  from  a 

Surf  jicc 

in  which  the  organisms  proliferate  to  an  unlimited 
degree^  and  from  which  they  reach  the  circulation 
more  or  less  continuously  in  large  numbers,  either 
in  a  living  or  dead  condition.  This  relates  particu- 
larly to  typhoid,  paratyphoid,  cholera  and  dysen- 
tery. They  are  primarily  surface  infections.  In 
the  two  former,  however,  the  organisms,  during 
the  early  days  of  infection,  reach  the  circulation  in 
a  living  condition  in  large  numbers,  and  may  even 
proliferate  in  this  situation.  In  cholera,  the  vibrios 
show  a  disposition  to  general  invasion,  but  appear 
to  be  killed  off  before  they  have  actually  pene- 
trated the  intestinal  wall.  The  same  condition 
probably  prevails  in  bacillary  dysentery.  It  is  the 
general  belief  that  the  intoxication  in  these 
instances  comes  about  through  the  disintegration 
of  the  micro-organisms,  as  a  consequence  of  w^hich 
a  poisonous  protoplasm  is  set  free.  This  conception 
has  its  origin  from  the  facts  that  it  has  been  diffi- 
cult or  impossible  to  obtain  potent  soluble  toxins 
in  culture  media,  and  that  the  bodies  of  the  killed 
organisms  are  sufficiently  toxic  to  explain  the 
intoxication.  Eecent  work,  however,  indicates  that 
a  certain  quantity  of  toxin  may  be  produced  in  arti- 
ficial cultivation,  and  it  is  possible  that  the  condi- 
tions in  the  body  are  much  more  favorable  for  ^- 

'^  _       ,  Clirojaic 

toxin  production  than  are  artificial  surroundings.   LoeaHzed 
Certain  chronic  infections,  even  when  they  involve  without 

J  ,.  1    •    J.  1  1  i  ji        Metastatic 

deeper  tissues  and  internal  organs,  show  from  the  Extension. 


98  IXFECTIOX    A\D    IMMUNITY. 

start  a  disposition  to  remain  localized,  although  in 
the  end  they  ma}'  involve  various  organs,  by  means 
of  metastases,  and  in  some  of  them  a  more  or  less 
continuous  blood  infection  may  arise.  Such  dis- 
eases are  tuberculosis,  actinomycosis,  blastomyco- 
sis (oidiomycosis),  rhinoscleroma,  sporotrichosis, 
and  perhaps  leprosy.  They  are  characterized  by 
the  formation  of  a  good  deal  of  fibrous  tissue, 
which  tends  to  limit  rapid  extension  by  the  forma- 
tion of  metastases,  and  by  a  disposition  to  invade 
contiguous  tissues.  iSTew  foci  may  be  set  up  in 
distant  organs  by  means  of  metastasis,  the  blood- 
stream in  the  meantime  being  comparatively  free 
from  living  micro-organisms.  A  true  septicemic 
condition  may  be  produced  in  tuberculosis  by  the 
sudden  pouring  of  large  quantities  of  bacilli  iato 
the  circulation  from  a  cheesy  focus  which  has 
ruptured  into  a  vessel.  This  again  results  in  the 
formation  of  many  minute  foci  in  various  parts 
of  the  body  (diffuse  miliary  tuberculosis).  The 
conditions  are  similar  in  blastom3Cosis,  leprosy 
and  glanders.  Earely  metastatic  infection  with 
actinom3'ces  is  found. 

These  chronic  infections  are  not  the  only  ones, 
however,  in  which  new  foci  may  originate  by 
metastasis.  A  streptococcus  infection  of  the  heart 
valves,  or  an  infected  thrombus  in  some  vein,  cause 
"pyemic"  abscesses  in  various  organs  when  infected 
clots  from  the  original  site  are  set  free  in  the  circu- 
lation. The  foci  of  infection  found  in  the  kidney  in 
typhoid  fever,  and  the  involvement  of  the  joints 
in  gonorrhea,  are  further  examples  of  metastatic 
invasion. 
Secondary  As  already  indicated,  systemic  infection  may 
infectioiiM.   take  place  in  a  secondary  and  accidental  way  in 


SYSTEMIC    INFECTIONS. 


99 


many  cases  when  a  pre-existing  local  disease  exists 
at  some  point.  In  a  small  group  of  diseases 
(typhoid^  paratyphoid,  pneumonia)  this  second- 
ary general  invasion  occurs  with  great  constancy, 
and  the  organisms  can  always  be  cultivated  from 
the  blood  if  this  is  undertaken  at  the  proper  time. 
In  syphilis  general  invasion  occurs  only  after  a 
certain  ^^incubation  period'^  has  been  passed  in 
the  primary  sore,  and  after  this  time  it  exists  as  a 
protracted  blood  infection. 

Others  appear  to  be  primarily  and  essentially  F^^^J"^?^ 
blood  infections,  little  or  no  reaction  taking  place  infections. 
at  the  point  of  invasion.  This  is  true  of  systemic 
plague,  anthrax,  Eocky  Mountain  spotted  fever, 
some  very  virulent  infections  with  the  streptococ- 
cus, relapsing  fever,  and  in  many  of  the  protozoan 
infections,  as  in  malaria,  piroplasmosis,  and  in 
sleeping  sickness.  In  some  of  these  the  organisms 
may  pass  a  portion  of  the  incubation  period 
in  the  lymph  glands,  where  they  proliferate 
to  such  an  extent  that  they  gradually  over- 
whelm the  circulation  in  large  numbers.  The 
organisms  of  malaria  and  piroplasmosis  proliferate 
in  the  blood-stream,  i.  e.,  within  the  erythrocytes. 
It  also  seems  probable  that  the  other  organisms 
mentioned  are  able  to  proliferate  in  the  plasma, 
and  that  their  presence  in  the  blood-stream  is  not 
due  entirely  to  their  continuous  escape  from  such 
solid  organs  as  the  lymph  glands  and  spleen,  or 
from  the  point  of  primary  invasion.  They  are  true 
or  full  parasites  in  the  sense  of  Bail. 

From  the  standpoint  of  continuity  there  are  sev- 
eral types  of  systemic  infection. 

We  may,  in  the  first  place,  recognize  the  continu-   continuons 

.  .  Systemic 

ous  t^'pe,  in  which  the  organisms,  after  they  once   infections. 


100  INFECTION    AND    IMMUNITY. 

reach  the  circulation,  persist  in  that  situation  until 
the  infection  terminates  either  in  death  or  recovery, 
in  the  latter  case  being  exterminated  by  the  pro- 
tective agencies  of  the  blood.  T3^phoid  and  para- 
typhoid fever,  plague,  Eocky  Mountain  spotted 
fever,  Malta  fever,  and  probably  the  acute  exanthe- 
mata, are  of  this  type.  Eecovery  and  the  steriliza- 
tion of  the  blood,  however,  does  not  mean  that  the 
whole  body  is  necessarily  rid  of  the  micro-organ- 
isms; the  latter  still  may  persist  for  a  greater  or 
less  period  on  one  or  more  of  the  body  surfaces,  as 
in  the  case  of  typhoid  fever,  in  which  the  bacilli 
may  persist  in  the  intestines  or  the  bladder  for  a 
long  period,  or  in  plague  in  which  the  organisms 
may  be  found  in  the  sputum  for  some  time. 
Through  some  accident  typhoid  may  vary  from  its 
usual  habit,  a  point  which  is  illustrated  by  the 
occasional  occurrence  of  relapses,  or  by  the  locali- 
zation of  the  bacilli  in  some  solid  organ  of  the 
body,  as  in  the  vertebrae  or  the  muscles,  resulting 
in  post-typhoidal  complications. 
I'eriodic  ^^^  otlicr  instances  the  systemic  invasion  is  of 
infecti^'sf.  periodic  character,  and  of  this  there  are  a  number 
of  varieties.  The  streptococcus,  when  it  exists  as 
the  cause  of  fibrinous  endocarditis  or  of  thrombo- 
phlebitis, often  invades  the  circulation  in  a  fluctu- 
ating manner.  Periods  when  there  are  very  few 
cocci  in  the  blood  will  be  followed  by  others  in 
which  they  are  very  numerous,  and  the  clinical 
symptoms  usually  correspond  with  these  fluctua- 
tions. A  similar  course  probably  is  foUawed  by 
tuberculosis  and  blastomycosis  in  their  invasion  of 
the  blood.  Mechanical  factors  sometimes  precipi- 
tate a  systemic  distribution,  such  as  the  rupture  of 
a  caseous  nodule  into  a  vessel  or  lymph  channel  in 


RECRUDESCENCES  IN  INFECTIONS. 


101 


Regular 
Recnrrences, 


tuberculosis,  or  the  separation  of  minute  fragments 
of  thrombus  infected  with  streptococci. 

Examples  of  a  more  or  less  regular  periodicity 
are  found  in  the  various  relapsing  fevers,  which 
are  caused  by  spirilla.  The  first  attack  of  the 
European  relapsing  fever  lasts  for  six  or  seven 
days.  This  is  followed  by  a  period  of  apyrexia  of 
five  or  six  days,  followed  by  another  febrile  period. 
Recovery  is  usually  established  after  three  or  four 
such  attacks.  In  the  relapsing  fever  of  South 
Africa  the  first  attack  has  a  shorter  duration 
(about  three  days),  and  those  which  succeed  may 
last  only  one  or  two  days,  according  to  Koch. 
During  the  febrile  attacks  the  blood  swarms  with 
spirilla,  whereas  in  the  intervals  it  is  compara- 
tively free  from  organisms.  In  explanation  of  this 
it  has  been  assumed  that  the  febrile  attacks  are  cut 
short  by  the  development  of  a  certain  degree  of 
immunity.  This  results  in  a  more  or  less  complete 
sterilization  of  the  blood,  although  spirilla  which 
remain  in  the  lymphoid  organs,  particularly  the 
spleen,  seem  to  be  protected.  At  the  time  of  a 
relapse,  either  the  immunity  has  decreased  sufii- 
cienth',  or  the  remaining  organisms  have  gained  in 
virulence  to  such  an  extent  that  a  general  reinva- 
sion  takes  place.  In  the  end  the  immune  forces 
gain  the  upper  hand  and  the  body  becomes  com- 
pletely sterilized. 

Some  of  the  chronic  infections  are  subject  to  ^f^J^'p*^^- 
irregular  recrudescences.  Syphilis  and  trypanoso- 
miasis of  man  begin  as  acute  infections.  After 
the  acute  secondary  stage  has  apparently  passed, 
syphilitics  frequently  suffer  recrudescences,  with 
general  manifestations,  and  it  is  probable  that  the 
number  of  micro-organisms  in  the  blood  increases 


cences  m 
Sypliilis,    etc. 


102  INFECTION    AND    IMMUNITY. 

at  such  times.  In  the  first  stage  of  sleeping  sick- 
ness, the  so-called  trypanosomatic  fever,  the  fever 
is  of  a  remittent  type,  and  during  the  attacks  of 
fever  the  number  of  trypanosomes  in  the  blood 
increases.  In  the  stage  of  sleeping  siclaiess  they 
appear  to  be  limited  very  largely  to  the  lymphatic 
glands  and  the  meninges.  They  can  readily  be 
obtained  from  these  sites  by  puncture,  but  their 
presence  in  the  blood  is  much  more  inconstant.  It 
has  been  the  experience  that  on  some  days  pro- 
longed examination  of  the  blood  will  disclose  no 
trypanosomes ;  on  other  days  two  or  three  per  field 
may  be  found ;  and  on  still  others  as  many  as  seven 
or  eight  per  field. 
Cyclic  The  tertian  and  quartan  infections  with  the 
'"^»iaiaria!  in^larial  parasites,  at  least  in  their  early  stages, 
illustrate  a  special  type  of  recurrent  generalized 
infection,  which  is  cyclic  in  nature,  the  period  of 
intense  general  invasion  coinciding  with  a  certain 
stage  of  the  asexual  multiplication  of  the  parasites. 
(See  chapter  on  malaria.) 

(S)   Nature  and  Mechanism  of  Infection. 

netration  i>y  ^^  ^^  to  be  understood  that  infection  presupposes 
Micro-  a  penetration  of  the  bodv  surfaces  to  a  greater  or 
less  degree.  Even  in  pityriasis  versicolor,  the 
most  superficial  of  infections,  the  fungus  pene- 
trates the  liorny  layer  of  the  skin.  Hence,  in  a 
consideration  of  the  nature  and  mechanism  of 
infection,  it  would  be  desirable,  first  of  all,  to  con- 
sider the  manner  in  which  micro-organisms  and 
their  poisons  may  reach  the  deeper  tissues.  In 
some  instances  this  is  readily  understood,  whereas 
in  many  others  we  must  in  the  main  be  content 
with  mere  deductions. 


ABSORPTION   OF   TOXINS. 


103 


Certain  animal  parasites^  as  the  itch  mite  and   skin. 
jigger^  jDenetrate  the  surface  through  mechanical 
defects  of  their  own  makinsf. 

In  penetratino^  wounds,  abrasions  and  transmis-  Mecimnicai 

,        .  .  -,  p        '  •  Iinplantatic 

sion  by  insects  the  introduction  of  micro-organisms 
is  a  question  of  mechanical  inoculation,  or  subse- 
quent growth  into  the  defect.  In  this  case  there  is 
no  barrier  to  their  entrance  into  the  circulation, 
until  after  the  appearance  of  an  inflammatory 
reaction;  and  if  the  organism  happens  to  be  one 
which  secretes  a  soluble  and  easily  diflusil)le  toxin 
(e.  g.,  tetanus  bacillus),  general  intoxication  may 
result  even  without  further  dissemination  of  the 
living  cells.  The  degree  of  defect  necessary  for 
infection  varies  with  the  character  and  virulence  of 
the  organism.  The  bacilli  of  plague,  anthrax, 
glanders,  and  the  spirochete  of  syphilis  may  enter 
through  lesions  which  are  almost  microscopic  in 
size.  These  organisms  possess  great  infectivity, 
exceedingly  small  numbers  producing  infection. 

Organisms,  such  as  virulent  staphylococci,  which 
reach  the  hair  follicles  and  sebaceous  glands,  are 
able  to  grow  through  the  succulent  epithelium  into 
the  surrounding  tissues,  and  to  cause  a  furuncle, 
carbuncle  or  cellulitis.  This  may  follow  or  be 
accompanied  by  a  primary  necrosis  of  the  epi- 
thelium. Occasionally  when  furuncles  are  situated 
at  favorable  spots,  as  near  the  angle  of  the  mouth 
or  nose,  the  necrosis  may  extend  to  adjacent  veins, 
resulting  in  a  flooding  of  the  circulation  with  the 
organisms. 

True  soluble  toxins  are  seldom  absorbed  through 
the  unbroken  skin,  if  we  except  the  case  of  poison- 
ing with  poison  ivy.  In  Moro's  test  for  tuberculo- 
sis   the    tuberculin,    incorporated    in    a    paste,    is 


Penetration,  by 

Contiguous 

GroTvtli. 


104 


INFECTION    AND    IMMUNITY. 


Mncons 
Surfaces. 


CoiitigTHOnN 


rubbed  into  the  skin.  This  is  also  true  of  most 
chemical  poisons  which  do  not  have  a  corrosive 
effect,  although  by  prolonged  contact  (lead)  or 
rubbing  (mercury)  a  certain  amount  of  absorp- 
tion may  be  induced. 

In  infections  of  the  mucous  membranes,  with 
their  soft  epithelial  covering  and  moist  surfaces, 
micro-organisms  are  often  able  to  grow  through 
into  the  underlying  tissue,  resulting  in  either  a 
local  inflammation,  a  general  infection  through 
the  medium  of  the  lymphatics  or  capillaries,  or  a 
general  intoxication  through  the  absorption  of 
toxins.  A  mechanical  defect  in  the  surface  may 
not  be  necessary  for  this  penetration,  the  exten- 
sion taking  place  by  contiguous  growth,  which. 
Growth,  however,  is  surely  favored  by  any  toxic  and  desqua- 
mating effect  which  the  organism  or  its  toxin  may 
have  on  the  epithelium.  Streptococci  which  reach 
the  crypts  of  the  tonsils  readily  cause  necrosis  of 
the  surface  epithelium,  and  this  defect  would  seem 
to  facilitate  deeper  invasion. 

The  growth  of  the  diphtheria  bacillus  is  limited 
in  the  main  to  the  superficial  layers  of  the  tissues 
which  it  attacks.  As  the  organism  penetrates  the 
epithelial  layer,  possibly  by  direct  growth,  the  toxin 
which  it  secretes  causes  necrosis  of  the  adjacent 
cells.  This  process  continues  until  the  vascular 
tissues  are  reached,  resulting  in  the  formation  of  a 
false  membrane.  However,  the  onset  of  fever 
before  the  formation  of  the  membrane,  and  the 
occurrence  of  diphtheria  without  membrane  forma- 
tion, show  that  the  false  membrane,  i.  e.,  the  necro- 
sis of  the  surface,  is  by  no  means  a  prerequisite  for 
the  absorption  of  the  toxin.  A  severe  invasion  of 
the  bod}^  by  the  bacillus  does  not  occur,  although 


Diplitiieriu. 


LEUCOCYTES   AS   CARRIERS.  105 

occasional  individuals,  without  doubt,  reach  the  cir- 
culation; this,  however,  is  not  necessary  for  the 
general  intoxication. 

Leucocytes  are  continuously  passinsr  from  the  Leucocytes 
tonsils,  intestines  and  other  superficial  organs 
which  are  rich  in  lymphatics,  through  the  mucous 
membrane  to  the  surface.  These  excreted  leuco- 
cytes may  often  be  seen  engorged  with  large  num- 
bers of  bacteria  which  they  encounter  on  the  sur- 
face, and  it  has  been  suggested  that  the  excreted 
leucocytes  may  re-enter  the  adjacent  tissue,  carry- 
ing bacteria  with  them.  The  study  of  sections  of 
the  intestines,  tonsils  and  peribronchial  lymph 
glands  has  shown  that  bacteria  are  continuously 
entering  the  bod3\  even  in  health,  and  their  fre- 
quent occurrence  within  leucocytes  which  are  near 
the  surface  suggests  that  the  latter  are  the  agents 
through  which  they  are  introduced  (Euffer,  Biz- 
zozero  and  others).  This  finding,  however,  could 
not  be  accepted  as  proof  of  the  hypothesis,  since 
the  phagocytosis  may  have  taken  place  after  the 
organisms  had  penetrated  the  surface  independ- 
ently. 

Through  the  work  of  Nocard,  Eavenel,  Behring 
and  others,  it  has  been  shown  that  tubercle  bacilli 
will  pass  into  the  lymphatics  from  the  intestines, 
in  the  absence  of  mechanical  defects. 

That  the  leucocytes  may  perform  this  function 
is  also  suggested  by  A.  B.  Macalluni's  study  of  the 
absorption  of  iron.  When  the  albuminate  and  pep- 
tonate  of  iron  were  fed  to  starved  lizards,  the  min- 
eral, eight  hours  later,  was  demonstrated  in  large 
quantities  in  the  leucocytes  contained  in  the  lumen 
of  the  intestines,  also  within  leucoc5^tes  which  lay 
between  the  epithelial  cells  of  the  villi  (re-entering 


ToTins. 


106  INFECTION    AND    IMMUNITY. 

leucocytes  ( !  )  ,and  within  similar  cells  which  were 
found  in  the  liver  and  spleen  (Adami's  Principles 
of  Pathology,  Vol.  T,  p.  291).  Inasmuch  as  no 
power  of  spontaneous  penetration  can  be  ascribed 
to  the  particles  of  iron,  it  is  held  that  they  were 
carried  into  the  tissues  by  inwandering  leucocytes. 

It  may  be  stated,  then,  as  a  reasonable  probabil- 
ity that  micro-oro;anisms  are  sometimes  carried  into 
the  deeper  tissues  by  leucocytes  which  re-enter  the 
surface. 

Phagocytosis  of  bacteria  by  epithelial  cells,  par- 
ticularly^ by  the  pulmonary  epithelium,  is  known  to 
occur,  but  it  is  not  known  that  the  process  is  an 
essential  one  for  invasion. 

Some  toxins  are  not  readily  absorbed  by  the  nor- 
mal mucous  membranes,  whereas  others  seem  to  be 
taken  up  readily.  In  the  absence  of  wounds,  tet- 
anus toxin,  when  ingested,  causes  no  symptoms. 
It  is  destroyed  largely  by  the  gastric  and  pan- 
creatic juices,  and  this  is  the  case  also  with  diph- 
theria toxin  in  test-tube  experiments.  The  latter 
has  the  power  of  causing  necrosis  of  the  mucosa, 
and  may  be  absorbed  through  the  injured  surface. 
The  toxin  of  hay  fever  is  readily  absorbed  through 
the  conjunctiva  and  the  mucous  membrane  of  the 
nose.  Experimentally,  ricin,  a  plant  toxin,  is 
absorbed  through  the  intestines,  although  the 
amount  required  for  fatal  intoxication  by  this 
route  greatly  exceeds  that  of  the  subcutaneous 
injection.  The  toxin  of  the  bacillus  of  botulism 
is  readily  absorbed  through  the  intestines  of  both 
man  and  animals. 
Denndation  When  a  micro-orgauism  causes  a  primary  des- 
quamation of  the  mucous  epithelium,  it  follows 
tliat  further  penetration  of  the  organism,  as  well 


of   Surface. 


INCUBATION   PERIOD. 


107 


as  absorption  of  toxins^  are  facilitated.  This  would 
seem  to  find  special  application  in  cholera  and 
bacillary  dysentery.  In  cholera  general  invasion 
of  the  body  by  the  living  organisms  does  not  take 
place,  although  the  intestinal  surface  is  denuded 
to  a  greater  or  less  degree.  The  vibrios  penetrate 
to  a  certain  rather  superficial  depth,  where  they 
appear  to  become  dissolved,  and  with  their  dissolu- 
tion, poisons,  in  addition  to  those  which  were  pre- 
viously secreted,  are  set  free.  The  conditions  are 
similar  in  dysentery. 

To  summarize,  micro-organisms  gain  entrance  to  summary. 
the  subjacent  tissues  through  wounds,  by  means  of 
their  own  power  of  injuring  the  surface  and  groov- 
ing into  and  through  it,  and  probably  also  through 
the  agency  of  inwandering  leucocytes.  Phagocytic 
epithelial  cells  in  some  instances  may  play  a  part, 
but  this  is  hypothetical.  Toxins  are  absorbed  for 
the  most  part  through  surfaces  which  have  been 
previously  injured,  but  some  of  them  are  able  to 
pass  through  previously  healthy  mucous  mem- 
branes. 

The  term  incubation  period  signifies  the  inter- 
val between  the  first  introduction  of  a  pathogenic 
micro-organism,  or  its  toxin,  until  the  develop- 
ment of  the  first  symptoms  which  characterize  the 
onset  of  the  disease.  In  many  infections,  as  in 
typhoid  fever,  a  feeling  of  malaise,  headache  and 
nausea,  frequently  appear  a  few  days  before  marked 
s3anptoms  develop,  and  this  period  is  called  the 
prodromal  stage.  It  may  be  considered  either  as 
the  latter  end  of  the  incubation  period,  or  as  the 
beginning  of  actual  "onset." 

The  length  of  the  incubation  period  varies 
greatly  in  different  infections.     In  cholera  it  may 


Incn'bation 
Period. 


Dnration. 


108  IXFECTJOX    AyD    IMMUXITY. 

be  as  short  as  a  few  hours  only,  in  h3^drophobia  it 
is  on  rare  occasions  as  long  as  six  months,  but 
more  commonly  two  to  four  weeks.  In  a  rather 
large  groujD  of  diseases  the  onset  follows  in  from 
one  to  two  weeks  after  exposure,  so  that  there 
would  seem  to  be  a  tendency  to  some  general  law, 
the  basis  of  which  is  not  known. 

It  has  been  suggested  that  it  may  have  a  relation 
to  the  anaphylactic  reaction  (Eosenau  and  Ander- 
son) ;  namely,  that  the  first  micro-organisms  intro- 
duced "sensitize"  the  body  in  some  way  not  3^ei 
understood,  and  when  sensitization  has  taken  place 
(seven  to  fourteen  days)  the  body  then  has  a 
greater  susceptibility  to  the  organism  and  yields 
readily  to  infection   (see  "Anaphylaxis"). 

Occasional  individuals  show  a  susceptibility  to  a 
first  injection  of  horse  serum  (e.  g.,  diphtheria 
antitoxin)  in  that  they  develop  an  urticarial  rash, 
adenopathy,  effusions  into  the  joints,  and  perhaps 
fever,  in  from  eight  to  twelve  days  after  the  intro- 
duction of  the  serum.  Von  Pirquet  noted  that 
when  a  second  injection  of  the  serum  was  given 
after  an  interval  of  two  weeks  or  more  similar 
symptoms  would  develop  within  a  few  hours  rather 
than  after  several  days;  and  there  is  a  great  deal 
of  constancy  in  this  when  susceptible  individuals 
are  concerned.  He  arrived  at  the  conclusion  that  the 
horse  serum  as  such  is  not  toxic  for  man,  but  that 
as  a  consequence  of  the  injection  antibodies  to  the 
serum  are  formed  and  that  the  intoxication  comes 
about  as  a  result  of  some  kind  of  chemical  reaction 
which  takes  place  between  the  antibodies  and  the 
serum.  The  conditions  in  immunization  render 
this  explanation  extremely  probable.  After  the 
first  injection  of  serum  antibodies  to  the  serum 


INCUBATION    AND    DOSAGE.  109 

(precipitating  and  perhaps  other  antibodies)  are 
found  in  considerable  concentration  in  the  blood 
only  after  the  lapse  of  some  days.  If  the  injection 
of  serum  given  in  the  first  place  was  of  some  size, 
some  of  the  original  serum  proteids  would  still  be 
present  in  the  body  when  the  antibody  formation 
had  reached  a  high  point,  and  the  conditions  for 
the  toxicogenic  reaction  between  the  two  would  be 
present.  This  would  account  for  the  delayed  reac- 
tion seen  in  first  injections.  If  some  smaller  quan- 
tity were  given  in  the  first  place  the  delayed  reac- 
tion might  not  occur,  because  the  serum  proteids 
would  all  have  been  modified  or  excreted.  If  a 
second  injection  is  given,  however,  the  fresh  serum 
at  once  comes  in  contact  with  the  antibodies  which 
have  already  been  formed,  and  the  toxic  combina- 
tion or  substance  can  be  produced  at  once. 

On  the  basis  of  these  considerations  von  Pirquet 
believes  that  the  ordinary  interpretations  of  the 
nature  of  the  incubation  period  are  incorrect. 
As  he  says :  "I  presented  the  theory  that  the  dis- 
ease-producing agent  only  calls  forth  pathological 
s3'mptoms  in  the  body  when  it  is  changed  by  means 
of  the  antibodies;  the  incubation  period  is  the 
period  required  for  the  formation  of  these  anti- 
bodies." This  possibility  cannot  be  overlooked 
in  a  present-day  consideration  of  this  subject, 
although  it  is  still  on  a  theoretical  foundation. 

The  number  of  micro-organisms  introduced  has 
an  influence  on  the  incubation  period.  Guinea- 
pigs  may  be  killed  within  a  few  hours  by  the  injec- 
tion of  a  large  quantity  of  typhoid  bacilli,  but  with 
the  administration  of  smaller  quantities  a  much 
longer  incubation  period  may  be  obtained.  The 
effect  of  quantity  also  is  shown  very  clearly  by  the 


Relation 
of  Dosage* 


110  IXFECTIOX    A^D    IMMUNITY. 

injection  of  diphtheria  or  tetanus  toxins,  by  which 
the  incubation  period  can  be  shortened  from  sev- 
eral days  down  to  several  hours,  depending  on  the 
quantity  injected. 

The  so-called  true  toxins  of  bacteria,  i.  e.,  those 
which  are  able  to  cause  the  formation  of  antitoxins, 
as  a  rule  are  distinguished  from  other  poisonous 
substances  of  bacterial  or  other  origin,  by  the  occur- 
rence of  an  incubation  period  when  they  are  admin- 
istered. However,  at  least  two  toxins,  venom  and 
that  secreted  by  the  Vibrio  Nasik  and  perhaps 
other  vibros,  act  so  quickly  that  an  incubation 
period  is  hardly  to  be  recognized. 
Proliferation.  The  number  of  micro-organisms  originally  enter- 
ing the  body  is  usually  quite  small;  hence  the  time 
required  for  them  to  reach  an  infective  or  toxic 
quantity  probably  represents  a  part  of  the  incuba- 
tion period. 
Meciianicni  In  hydrophobia  and  tetanus  a  mechanical  fac- 
tor plays  a  part  in  the  length  of  this  stage.  In 
these  cases  the  micro-organisms  (hydrophobia)  and 
toxin  (tetanus)  appear  to  reach  the  central  nerv- 
ous system  by  way  of  the  peripheral  nerves,  and 
symptoms  are  delayed  until  this  occurs.  Wounds 
of  the  face  and  neck  are  followed  by  symptoms 
more  quickly  than  when  they  are  situated  on  parts 
more  remote  from  the  central  nervous  system. 
Adaptation.  It  is  uot  Unlikely  that  another  factor  consists  of 
a  certain  relation  between  the  protective  powers  of 
the  host  and  the  invasive  or  aggressive  ability  of 
*  the  organism,  at  least  in  some  instances.    Lemaire 

and  also  Buxton  found  that  after  the  injection  of 
pathogenic  micro-organisms  directly  into  the  cir- 
culation, there  is  at  first  a  reduction  in  their  num- 
ber,   followed    by    renewed    proliferation,    whicli 


^ERUM   RESIST A'SGE   OF  ORGANISMS.       Ill 

progresses  stead  ii}-.  SiTpposedly,  the  natural  anti- 
bacterial forces  of  the  serum  and  leucocytes  took 
up  the  destruction  of  the  bacteria  until  the  former 
were  exhausted,  and  from  this  time  proliferation 
could  take  place  with  little  hindrance.  In  infec- 
tions which  occur  naturally,  as  in  typhoid  fever  or 
scarlet  fever,  the  first  organisms  which  reach  the 
underlying  tissues  and  circulation  may  be 
destroyed,  involving  such  a  loss  of  bactericidal 
agencies  that  continued  proliferation  and  invasion 
finally  results  in  general  infection. 

In  speaking  of  passage,  it  has  already  been  "Serum 
stated  that  virulence  may  he  increased  by  permit- 
ting an  organism  to  grow  in  the  tissues  of  a  living 
animal.  Virulent  organisms  are  not  taken  up  by 
leucocytes  so  readily  as  avirulent,  and  in  the  pres- 
ence of  high  virulence  there  may  be  no  phagocytosis 
at  all.  This  has  a  bearing  on  the  incubation  period 
in  that  the  micro-organisms  which  first  come  in 
contact  with  the  tissues  of  the  host  may  have  low 
virulence,  but  after  exposure  to  the  germicidal 
substances  for  a  sufficient  length  of  time,  their 
pathogenicity  and  resistance  may  be  so  raised  that 
they  escape  destruction  in  the  tissues.  On  this 
basis,  therefore,  the  incubation  period  may,  in  part, 
represent  the  time  required  for  the  organisms  to 
becomiC  serum-resistant. 

Eegarding  the  subject  under  discussion,  there  is 
still  another  factor  which  finds  application,  par- 
ticularly where  toxins  having  an  enzyme-like 
nature,  are  involved.  Toxins  have  been  likened  to 
enzymes,  because  of  their  action  in  exceedingly 
small  doses,  their  common  susceptibility  to  heat, 
and  finally  the  exhibition  of  an  incubation  period. 
ISTo  matter  how  much  diphtheria  or  tetanus  toxin 


112  INFECTION    AND    IMiWNITY. 

is  introduced  into  an  animal,  the  incubation  period 
cannot  be  eliminated  absolutely;  and  some  of  the 
hemolytic  toxins,  as  tetanolysin,  can  be  added  to 
red  blood  cells  in  test-tubes  in  any  desired  quan- 
tity Avithout  causing  their  immediate  solution. 
There  is,  therefore,  something  inherent  in  the 
nature  of  these  substances,  or  in  the  nature  of  the 
action  which  they  exert  on  the  cells  of  the  bod}^, 
which  demands  this  latent  period  before  an  effect 
becomes  manifest. 
Summary.  It  sccms  probable,  therefore,  that  there  are  many 
factors  which  contribute  to  the  existence  of  the 
incubation  period,  and  that  the  factors  which 
determine  its  length  in  one  instance  may  not  be 
identical  with  those  which  are  found  in  another. 
The  time  required  for  proliferation  of  the  micro- 
organism to  an  infective  quantity  probably  is  com- 
mon to  all  infections.  The  infective  quantity  must 
vary  with  different  diseases,  and  with  different 
strains  of  the  same  micro-organism  depending  on 
their  virulence.  A  virulent  strain  has  a  shorter 
incubation  period  than  a  less  virulent.  In  some 
instances  a  certain  amount  of  time  may  be 
required  for  the  micro-organism  to  undergo  an 
increase  in  virulence  sufficient  to  accomplish  infec- 
tion. Or,  again,  this  time  may  be  required  for  the 
exhaustion  (absorption  or  chemical  binding)  of 
the  protective  substances  to  such  a  degree  that  fur- 
ther proliferation  and  invasion  take  place  with 
greater  rapidity,  this  latter  step  coinciding  with 
the  onset  of  marked  symptoms.  The  time  required 
for  distribution  of  the  poisons  to  vital  organs  would 
seem  to  be  of  minor  importance  except  in  hydro- 
phobia and  tetanus,  which  utilize  the  peripheral 
nerves  as  a  route  to  the  central  nervous  system. 


AFFINITIES   OF   TOXINS. 


113 


In  the  case  of  some  of  the  toxins  (as  of  diphtheria 
and  tetanus)  a  certain  time  for  the  manifestation 
of  a  toxic  effect  is  required,  even  when  they  are 
placed  in  direct  contact  with  the  cells  for  which 
they  have  a  specific  affinity.  As  stated,  the  role  of 
anaphylaxis  is  uncertain. 

Leaving  out  of  consideration  the  few  instances 
in  which  preformed  toxins  are  ingested  and 
absorbed  (as  in  botulism),  the  production  of  dis- 
ease in  a  susceptible  host  would  seem  to  depend  on 
two  factors :  First,  presence  in  the  micro-organism, 
or  secretion  by  it,  of  a  toxin  which  is  able  to  cause 
a  direct  injury  of  the  tissues  of  the  host;  and  sec- 
ond, ability  of  the  micro-organism  to  remain  ali\^e 
and  to  proliferate  in  the  body  of  the  host. 

Different  toxins  vary  greatly  in  the  cells  which 
they  attack.  Some  destroy  the  red  blood  cells  to  a 
marked  degree  (staphylococcus  and  streptococcus)  ; 
others  have  a  special  affinity  for  the  nervous  tissue 
(tetanus,  diphtheria,  botulism) ;  some  attack  par- 
ticularly the  endothelium  of  the  vessels,  causing 
many  minute  hemorrhages  (some  of  the  eruptive 
fevers,  rattlesnake  venom).  In  many  other  in- 
stances the  toxins  have  a  wider  range  of  action, 
and  many  different  tissues  suffer  to  a  greater  or 
less  degree.  Areas  of  necrosis  in  the  l3^mphoid  and 
parenchymatous  organs,  and  granular  and  fatty 
degeneration  of  the  latter,  and  of  the  muscles, 
including  the  heart,  are  well  known  in  different 
diseases.  The  albumin  and  casts  which  appear  in 
the  urine  in  various  acute  febrile  diseases  are  a 
result  of  a  toxic  action  on  the  epithelium  and  endo- 
theliimi  of  the  kidneys. 

In  addition  to  destroying  life  by  their  direct 
action   on   the   cells,   pathogenic   micro-organisms 


Factors   in 
Establisli- 
meut  of 
Infection. 


Direct 

Clieinical 

Injuries. 


114  INFEGTIOX    AXD    UIMUNITY. 

produce  profoimcl  disturbances  in  metabolism  and 
nutrition  by  interference  with  the  functions  of 
organs.  It  is  not  the  intention,  however,  to  enter 
into  a  discussion  of  these  obscure  influences. 

3ieciianicfti  The  mechauical  injuries  which  micro-organisms 
cause  are,  at  least  in  most  cases,  the  result  of  a 
previous  toxic  action,  i.  e.,  they  are  secondary 
effects.  This  is  true  of  the  emboli,  consisting  of  a 
mixture  of  fibrin,  cells  and  micro-organisms,  which 
arise  in  a  valvular  endocarditis,  and  of  thrombi 
•  which  are  formed  in  vessels  as  a  consequence  of 
infection. 
Fibrin.  [j^  lobar  pncumonia  we  have  a  good  example  of  a 
mechanical  disturbance  of  importance.  The  alveoli 
become  filled  with  a  fibrinous  and  purulent  exudate 
which  makes  a  large  area  of  pulmonary  tissue 
unavailable  for  respiration.  Yet,  even  here,  the 
mechanical  disturbance  has  arisen  only  as  a  result 
of  the  toxic  action  of  the  pneumococcus  on  the 
capillary  walls  and  the  alveolar  epithelium,  per- 
mitting the  escape  of  the  blood  and  serum. 

Connective       Somc  chronic  infections  are  characterized  by  the 

Tissue. 

development  of  new  connective  tissue  and  vessels ; 
this  is  seen  especially  in  syphilis,  tuberculosis  and 
actinomycosis.  The  import  of  the  new  connective 
tissue  depends  on  its  location.  A  large  amount  of 
it  may  form  in  pre-existing  fibrous  tissues  with  no 
consequent  harm;  but  even  a  small  scar,  gumma 
or  tubercle  in  the  brain,  or  deformities  of  the  heart 
valves  which  follow  inflammation,  may  cause 
serious  results. 
Malaria.  A  genuine  direct  mechanical  disturbance  appears 
to  be  caused  by  the  malarial  organisms  in  that 
they  occasionally  accumulate  in  the  capillaries  of 
the  intestines  and  brain  in  such  numbers  as  to 


RESISTANCE    OF    ORCJAyiSMS. 


115 


Anti- 
infection.s 
Hnd  Antitoxic 
Agreweies. 


amount  to  virtual  thrombosis.  Filarial,  which  are 
multicellular  organisms^  cause  grave  conditions  by 
occlusion  of  the  lymphatics. 

In  discussing  the  second  condition  for  the  occur- 
rence of  infection,  namely,  the  ability  of  the 
micro-organism  to  remain  alive  and  to  proliferate 
in  the  body  of  the  host,  this  must  be  done  with 
regard  to  certain  protective  agencies  which  the  host 
possesses  against  invading  micro-organisms. 

x\s  will  appear  later  in  more  detail,  these  agencies 
may  be  directed  either  against  the  toxins  of  the 
micro-organisms,  or  against  the  parasitic  cells 
themselves.  The  former  rests  in  the  antitoxins 
which  may  be  present  in  the  plasma  and  lymph, 
and  the  power  of  the  tissues  to  bind  and  destroy 
the  toxins;  the  latter  in  the  germicidal  substances 
of  the  body  fluids  (the  so-called  bacteriolysins), 
and  in  th6  phagocytic  and  destructive  action  of 
various  cells  of  the  body,  particularly  the  leucocytes 
and  endothelial  cells.  Manifestly,  in  actual  infec- 
tion the  micro-organisms  are  able  to  proliferate  in 
spite  of  the  presence  of  these  antagonistic  agencies, 
and  the  conditions  which  render  this  possible  prob- 
ably vary  a  great  deal  in  different  infections. 

Thus,  in  relation  to  tuberculosis,  either  the  Natural 
serum  of  man  and  animals  possesses  no  germicidal 
substances  for  this  particular  organism,  or  the  lat- 
ter is  resistant  to  their  action.  Also,  since  the 
bacilli  are  frequently  found  within  phagocytic 
cells  in  a  good  state  of  preservation,  it  would 
seem  that  thev  have  a  certain  deoTee  of  resistance 
to  intracellular  digestion.  Staphylococci,  strepto- 
cocci and  certain  other  organisms  resist  destruction 
by  the  serum,  although*"  they  are  readily  taken  up 
and  destroyed  by  phagocytes. 


Resistance  of 
Organisms. 


116  INFECTION    AND    IMMUNITY. 

Acquired  Tliis  insusceptibility  of  the  tubercle  bacillus  and 
^*orsanism*s*  ^hc  cocci  mentioned  to  the  germicidal  action  of 
the  serum  is  a  natural  and  constant  propert}^  On 
the  other  hand,  certain  organisms  which  are  nat- 
urally susceptible  to  the  germicidal  power  of  the 
serum  and  leucocytes  appear  to  acquire  a  resistance 
against  these  agencies  during  the  course  of  infec- 
tion, and  it  is  not  at  all  unlikely  that  this  is  a 
property  which  is  common  to  all  pathogenic  micro- 
organisms. We  may  look  on  this  change  as  a 
phenomenon  of  adaptation.  In  a  distinct  sense  it 
appears  that  the  micro-organisms  ma}^  become 
immunized  to  the  bactericidal  substances  of  the 
serum,  and  to  the  opsonins  on  which  destruction 
by  phagocytosis  depends. 

The  increase  of  virulence  in  a  micro-organism 
by  repeated  passage  through  a  suitable  animal  may 
be  regarded  as  an  adaptation  on  the  part  of  the 
organism  for  the  tissues  and  fluids  of  the  animal, 
and  in  this  adaptation  an  increased  resistance  to 
the  germicidal  substances  probably  is  an  important 
factor.  Similar  agencies  doubtless  are  at  work  in 
the  maintenance  of  virulence  by  growing  cultures 
on  media  which  contain  the  serum  of  animals. 

Typhoid  bacilli  which  have  been  cultivated  from 
the  body  of  a  patient  recently  are  more  resistant 
to  agglutination  than  those  which  have  been  on 
artificial  media  for  some  time.  The  same  has  been 
found  true  of  the  cholera  vibrio  (Pfeiffer  and 
Kolle),  as  well  as  of  some  other  organisms.  Also 
the  cultivation  of  bacteria  (typhoid  bacilli)  in 
media  which  contain  an  agglutinating  serum  brings 
about  an  increased  resistance  to  agglutination 
(Eansom  and  Kitashima,  Walker,  Steinhardt  and 
others)  ;  and  it  has  been  shown  that  such  modified 


Resistance   to 
AgrerlntininM. 


BACTERWLYSINS.  117 

bacilli  absorb  or  bind  less  agglutinin  than  "nor- 
maF^  strains  (Miiller,  Cole,  Eisenberg).  Explained 
in  terms  of  Ehrlich's  theory,  it  is  assumed  that 
they  contain  a  decreased  number  of  binding 
molecules  or  receptors  for  the  agglutinin,  hence  an 
effective  quantity  of  the  latter  is  not  bound. 

Experiments  by  many  observers  indicate  that  Resistance  to 
bacteria  may  also  acquire  resistance  to  the  bac-  lysins. 
tericidal  action  of  the  serum,  and  that  this  prop- 
erty goes  hand  in  hand,  at  least  to  a  certain  extent, 
with  the  virulence  of  the  micro-organism.  In  some 
of  these  experiments  the  resistance  has  been 
acquired  by  growing  the  organisms  in  the  corre- 
sponding antiserum,  for  a  greater  or  less  length 
of  time.  Thus  Cohn,  by  growing  the  typhoid 
bacillus  on  antityphoid  serum,  conferred  on  it  an 
increased  resistance  to  bacteriolysis,  which  was 
retained  for  several  subsequent  generations  on  agar. 
Day  also,  in  a  similar  way,  caused  increased  serum 
resistance  in  B.  prodigiosus,  B.  vulgaris  and  B. 
ftuorescens,  and  even  conferred  some  pathogenic 
powers  on  these  organisms,  which  naturally  are 
rather  harmless  saprophytes.^  Such  results  have 
been  obtained  with  the  organisms  of  typhoid 
(Walker,  Haflkine  and  others),  cholera  (Szekely, 
Ransom,  Kitashima  and  others),  dysentery  (Mar- 
shall, Knox,  Mason),  anthrax  (Shaw,  Danyz  and 
others),  the  colon  bacillus  (Hamburger),  Vibrio  ^ 
metchnihovi  (Metchnikoff,  Bordet  and  others).  It 
has  frequently  been  found  also  that  bacteria  when 
freshly  cultivated  from  infections  have  an 
unusually  high  resistance  to  the  bactericidal  action 
of  serums.    Besserer  and  Jaffe  noted  that  a  strain 

1.  Eisenberg  gives  a  summary  of  this  and  kindred  subjects 
in  the  Centralbl.  f.  Bakteriol.,  etc.,  xlv,  No.  2. 


118  IXFECTIOX    AXD    IMMUNITY. 

of  the  typhoid  bacillus  isolated  from  a 
ma}^  show  tliis  increased  resistance. 
Resistance  to       It  is  an  old  tenet  of  Metchnikoff  that  virulent 

Pba&ocytosis.  .  ,  j.-i  i      i.        i  x 

micro-organisms  are  less  susceptible  to  phagocyto- 
sis than  avirulent.  This  was  supposed  to  be  due 
to  the  establishment  of  a  negative  chemotaxis, 
which  consisted  either  in  a  repelling  of  the  leuco- 
cytes or  in  their  failure  to  be  attracted  to  the  bac- 
teria. In  1892  Massart  reported  that  leucocytes 
were  negative  chemotactically  to  virulent  strains  of 
the  organisms  of  anthrax,  chicken  cholera,  swine 
plague,  and  to  B.  pyocyaneus  and  Vibrio  metchni- 
kovi,  and  that  they  were  taken  up  by  leucocytes  in 
the  animal  experiment  to  a  much  less  extent  than 
avirulent  strains  of  the  same  organisms.  The  same 
condition  was  noted  in  relation  to  staphylococci 
(van  der  Velde,  Kocher,  Taval).  Since  phagocy- 
tosis has  been  studied  more  extensively  under  arti- 
ficial conditions,  the  same  phenomenon  has  been 
noted  in  relation  to  other  organisms,  as  the  strepto- 
coccus (Hektoen  and  Euediger,  Bordet,  etc.), 
pneumococcus  (Eosenow),  typhoid  and  paraty- 
phoid bacilli  (Neufeld  and  Htine,  Hektoen),  the 
colon  bacillus  (Beattie),  the  meningococcus  (Flex- 
ner),  and  others.  In  African  tick  fever,  Levaditi 
and  Roche  noted  the  presence  of  spirillicidal  and 
opsonic  substances  (those  favoring  phagocytosis) 
following  the  first  attack  of  fever,  but  they 
appeared  to  be  effective  only  on  the  spirilla  which 
were  present  in  the  blood  during  the  first  attack. 
By  the  time  the  second  attack  occurred  the  organ- 
isms had  acquired  a  resistance  to  these  substances 
which  they  retained  during  several  passages 
through  rats  subsequently.  It  would  seem  that 
this  acquired  resistance  on  the  part  of  the  organ- 


RESISTANCE    TO    DRUGS.  110 

isms  is  what  makes  the  second  attack  possible,  and 
that  this  might  go  indefinitely  were  it  not  that  the 
host  eventually  responds  by  the  production  of 
such  a  quantity  of  germicidal  substances  that  the 
spirilla  are  finally  destroyed.  We  may  suppose 
that  the  conditions  are  not  very  different  in  syph- 
ilis and  in  some  of  the  chronic  protozoic  infections, 
as  trypanosomiasis  and  piroplasmosis;  in  all  these 
diseases  specific  antibodies  are  produced  during  the 
course  of  infection,  and  there  is  good  reason  to 
believe  that  some  of  these  are  germicidal  in  charac- 
ter. This  is  certainly  true  in  regard  to  piroplasmo- 
sis and  tr3q3anosomiasis,  3^et  the  organisms  persist 
in  the  blood  and  tissues  of  the  host  for  a  long 
period.  It  seems  that  they  must  have  become 
adapted  to  the  presence  of  these  germicidal  sub- 
stances. That  virulence  is  not  lost  as  a  consequence 
of  this  adaptation  is  shown  by  the  fact  that  the 
blood  wdien  it  is  injected  into  a  fresh  animal  repro- 
duces a  typical  acute  attack. 

It  is  noteworthy  that  a  similar  resistance  to  cer-  Acapired 
tain  drugs  can  be  induced  in  trypanosomes  when 
infected  animals  are  given  repeated  injections  of 
these  loreparatoins.  If  a  sufficient  quantity  of  one 
of  these  drugs  (atoxyl,  fuchsin,  tr^^pan-red,  etc.) 
is  given  to  an  infected  animal,  a  complete  cure, 
with  sterilization  of  the  bod}^,  may  be  obtained.  In 
the  event,  however,  that  an  insufficient  quantity 
of  the  drug  is  administered,  the  organisms  when 
injected  into  a  subsequent  animal  may  be  entirely 
indifferent  to  the  presence  of  the  drug,  which,  con- 
sequently, has  lost  its  therapeutic  value  against 
this  strain.  It  may  be  necessary  to  repeat  this 
process  through  many  passages  before  a  high  degree 
of  drug  resistance  is  obtained,  but  when  once  estab- 


Resi&tance 
to   Drn^s. 


120  I^FECTIO^N    AXD    IMMUNITY. 

lislied  it  is  of  long  duration.  Such  strains  are 
called  "chemoresistant."  It  has  also  been  shown 
that  trypanosomes  acquire  a  resistance  to  the 
germicidal  properties  of  serum,  as  in  the  case  of 
bacteria. 
Capsule  In  view  of  the  fact  that  some  micro-organisms 
produce  a  capsule  when  grown  in  the  animal  body, 
whereas  it  is  absent  in  ordinary  culture  media,  it 
has  been  supposed  by  some  that  the  capsule  is  an 
expression  of  adaptation  on  the  part  of  the  organ- 
ism to  the  germicidal  agencies  of  the  host,  that  it 
is  perhaps  protective  in  its  character.  Such 
observations  have  been  made  in  relation  to  the 
anthrax  bacillus  (Deutsch  and  others),  the  strep- 
tococcus (Bordet,  Marchand  and  others),  and  the 
plague  bacillus  (Lohlein).-  This  relationship,  how- 
ever, is  not  general;  and  can  hardly  be  considered 
as  thoroughly  established. 
p'rotective  ^^  addition  to  this  more  or  less  passive  adapta- 
Agencies.  tion  on  the  part  of  micro-organisms,  there  is  rea- 
son to  believe  that  they  may  actually  antagonize 
the  protective  agencies  of  the  body,  particularly 
the  process  of  phagocytosis.  Arloing  and  Cour- 
mont,  and  Eoger  believed  that  bacteria  secrete  sub- 
stances which  favor  their  growth  in  the  body. 
Eoger  observed  that  an  extract  of  the  bacillus  of 
symptomatic  anthrax  when  injected  into  the  rabbit 
favored  infection  with  this  organism.  Bouchard 
spoke  of  such  elements  as  substances  favorisantes. 
Kruse  {Zeiglers  Beitrage,  \\i,  339)  also  believed 
that  such  substances  exist  and  called  them  collect- 
ively hjtische  Sustanzen,  Angriffstoffe,  oder  Lysine. 
He  supposed  that  their  effect  was  chiefly  to  neu- 
tralize the  alexins,  the  name  which,  at  that  time, 

2.  Cited  by  Eisenberg,  1.  c. 


LEUGOCIDIN. 


121 


was  apjolied  to  the  bactericidal  substances  of  the 
serum.  Their  existence  had  no  satisfactory  sup- 
port at  that  time. 

A  little  later  van  der  Velde  discovered  that  Leucocidiu. 
staphylococci  secrete  a  substance  which  is  toxic  for 
leucocytes,  the  so-called  leucocidm.  It  appeared  to 
be  produced  by  strains  of  both  high  and  low  viru- 
lence. Still  more  recently  it  was  discovered  that 
the  streptococcus  produces  a  toxin  which  is 
destructive  for  leucocytes  (Ruediger,  Besredka). 
These  results  suggest  that  a  toxic  action  on  the 
leucocytes  may  be  a  factor  for  the  progress  of 
infection,  and  may  explain,  at  least  in  part,  the 
resistance  which  virulent  organisms  show  toward 
phagocytosis.  A  particularly  significant  observa- 
tion is  that  by  Eosenow,  to  the  effect  that  virulent 
pneumococci  secrete  a  substance  which  has  the 
power  of  inhibiting  phagocytosis,  a  substance  to 
which  the  name  of  virulin  was  given.  Virulin  can  vimiin. 
be  extracted  from  virulent  cultures  by  means  of 
salt  solution,  and  after  this  has  taken  place  the 
cocci  have  become  susceptible  to  phagocytosis.  Also 
after  avirulent  strains  have  been  treated  with  the 
extracted  virulin,  and  later  separated  from  it  by 
washing,  they  are  found  to  have  acquired  resist- 
ance to  phagocj'tosis.  Eisenberg  also  observed  that 
leucotoxic  substances  are  produced  by  the  bacilli  of 
symptomatic  anthrax  and  malignant  edema.  He 
furthermore  believes  that  it  is  a  more  or  less  com- 
mon property  of  bacteri'a  to  produce  such  sub- 
stances in  the  course  of  infection,  although  they 
may  not  be  obtained  under  artificial  conditions, 
and  that  they  are  identical  with  the  "aggressins" 
of  Bail.  The  correctness  of  this  belief,  however. 
is  not  fully  demonstrated. 


122  INFECTION    AND    IMMUNITY. 

As^ressins.  Bail,  discrediting  the  importance  of  the  germi- 
cidal substances  of  the  serum  for  natural  immun- 
ity, assigns  to  phagoc3'tosis  the  essential  role,  and 
believes  that  the  virulence  of  the  parasites  depends 
on  their  power  to  produce  substances,  the  aggres- 
sins,  which  antagonize  the  process  of  phagocytosis. 
The  aggressins  were  supposed  to  be  non-toxic  sub- 
stances which  were  produced  only  in  the  body  of 
the  infected  animal.  When  the  organisms  of 
typhoid,  cholera,  tuberculosis  and  other  diseases, 
are  injected  intraperitoneally  into  the  guinea-pig, 
the  aggressins  appear  in  the  inflammatory  exudate, 
and  are  obtained  free  from  living  micro-organisms 
by  centrifugation  and  subsequent  chemical  sterili- 
zation of  the  overlying  fluid.  This  fluid,  when 
mixed  with  the  homologous  culture,  has  the  power 
of  rendering  fatal  a  quantity  of  the  culture  wliich 
otherwise  would  be  unable  to  produce  infection, 
and  the  mixture  may  cause  a  very  acute  deatli  of 
the  experiment  animal.  Bail  found  all  the  more 
justification  for  assuming  the  existence  of  this  new 
(?)  substance  from  the  fact  that  immunization 
with  the  aggressins  gives  rise  to  a  serum  which 
has  the  power  of  neutralizing  the  effect  of  the 
aggressive  exudate;  hence  such  a  serum  was  termed 
an  antiaggressin. 
Objections.  The  studics  of  others,  however  (Wassermann  and 
Citron,  Doerr,  Sauerbeck  and  others)  indicate  that 
the  aggressins  of  Bail  do  not  represent  a  new  entity. 
Wassermann  and  Citron  found  that  the  "aggres- 
sins" as  prepared  by  Bail  are  toxic,  and  that  they 
may  be  obtained  in  artificial  cultures  as  well  as  in 
the  body  of  an  animal.  They  probably  represent 
nothing  more  than  the  cytoplasm  of  dissolved  bac- 
teria which  may  exert  an  inhibiting  effect  on  pha- 


ADAPTATION    OF   ORGANISMS.  123 

gocjtosis  in  more  than  one  way.  The  toxic 
substances  may  injure  the  leucocytes  to  such  an 
extent  that  they  do  not  readily  take  up  the  living 
organisms;  since  they  represent  disintegrated 
organisms,  they  ma}',  like  the  latter,  absorb  or 
^^bind"  the  opsonins  of  the  plasma,  on  which 
phagocytosis  depends,  and  thus  prevent  the  action 
of  the  opsonins  on  the  bacterial  cells;  similarly, 
they  bind  the  bacteriol3'sins  of  the  serum,  and 
hence  divert  their  action  from  the  living  cells; 
also,  since  the  dissolved  organisms  are  toxic,  when 
the  ^'^aggressins"  are  added  to  living  cultures,  the 
total  toxicity  for  the  animal  is  increased  by  just 
that  much.  There  is  also  evidence  to  show  that  the 
most  indifferent  proteid  substances  when  injected 
into  an  animal  may  decrease  its  resistance  to  infec- 
tion or  intoxication  for  the  moment.  Thus  Pack 
etts  and  Kirk  found  that  a  small  quantity  of  egg 
albumin,  broth,  or  normal  serums  (goat,  guinea- 
pig)  when  injected  into  white  mice,  decrease  the 
resistance  of  the  latter  to  a  concomitant  inocula- 
tion with  tetanus  toxin.  The  foreign  substances 
were  supposed  to  pre-engage  the  absorptive  and 
digestive  powers  of  various  cells  (leucoc3'tes,  etc.), 
so  that  the  toxin  was  disposed  of  less  readil}',  and 
more  remained  available  for  the  highly  susceptible 
nervous  tissues. 

The  remarks  just  made  are  not  intended  to  cast 
doubt  on  the  probability  that  pathogenic  micro- 
organisms produce  substances  which  are  antago- 
nistic to  phagocytosis.  That  the  latter  action 
really  occurs  has  already  been  indicated. 

In  previous  paragraphs  attention  was  called  to  Response  ana 
the  fact  that  micro-organisms  attempt  to  adapt  th^^ost?"  ^ 
themselves  to  their  hosts,  to  the  end  that  the  latter 


124  IXFEGTIOX    A^D    IMllUXITY. 

may  be  a  more  favorable  medium  for  their  exist- 
ence. Thus,  the}^  increase  in  virulence,  and  disarm 
the  host  by  becoming  resistant  to  its  protective 
agencies,  and  even  actively  antagonize  the  latter, 
particularly  as  regards  phagoc3'tosis,  and  by  such 
means  the  natural  immunity  of  the  host  is  rendered 
inefficient.  The  host,  however,  is  not  without  its 
own  reserve  forces,  and,  in  favorable  cases,  after 
infection  is  once  established,  it  responds  to  the  pres- 
ence of  the  micro-organisms  by  the  production  of 
a  new  supply  of  protective  "antibodies,''  the  effect 
of  which  is  to  destroy  larger  numbers  of  the  invad- 
ing organisms,  or  even  to  sterilize  the  body  com- 
pletely. In  the  latter  case  recovery  is  the  prob- 
able event.  This,  again,  may  be  looked  on  as  a 
process  of  adaptation  on  the  part  of  the  host,  in 
which  it  seeks  to  destroy  or  render  less  noxious  the 
infecting  microbes. 
Mntuai       In  certain  chronic   infections  it  seems  that  a 

Adaptation. 

mutual  adaptation  takes  pJace,  so  that  there  is  a 
tendency  for  the  host  and  parasite  to  live  in  a  half- 
way state  of  harmony.  Thus,  in  the  acute  stage 
of  syphilis,  the  "combat"  between  the  host  and  the 
spirochetes  is  an  active  one.  Eventually,  however, 
it  would  seem  that  the  host  reacts  by  the  produc- 
tion of  protective  antibodies,  a  condition  which 
results  in  an  amelioration  of  the  symptoms.  Since 
the  micro-organisms  may  remain  alive  and  viru- 
lent in  the  host  for  a  long  time  after  this  has 
occurred,  it  appears  that  they  become  habituated 
to  the  presence  of  the  antibodies,  while  the  host 
at  the  same  time  becomes  habituated  to  the  toxicity 
of  the  spirochetes.  After  the  lapse  of  still  further 
time  the  adaptation  on  the  part  of  the  patient 
appears  to  increase,  and  the  micro-organism  also 


IMMUNIZING    RESPONSE. 


125 


loses  in  virulence,  if  we  may  judge  from  the  low 
infeetivity  usually  accredited  to  tertiary  lesions, 
in  spite  of  the  fact  that  they  contain  the  spiro- 
chetes. This  mutual  adaptation,  however,  does  not 
mean  that  the  host  escapes  injury  as  a  consequence 
of  the  infection.  Similar  conditions  probably  pre- 
vail in  piroplasmosis  and  trypanosomiasis,  or  even 
in  relapsing  fever,  as  suggested  previously. 

What  has  come  to  be  known  as  the  hypothesis  of  Hypothesis 
Welch  may  be  mentioned  in  this  connection.  It 
may  be  put  in  the  form  of  the  following  question : 
If  bacterial  toxins  and  the  constituents  of  bacterial 
cells  so  act  on  the  tissue  cells  that  the  latter  pro- 
duce bodies  (antibodies)  which  are  inimical  to  the 
bacteria,  why  may  not  the  body  fluids  in  turn  so 
act  on  the  bacteria  that  the  latter  produce  bodies 
(antibodies)  which  are  inimical  to  the  tissue  cells? 
"Looked  at  from  the  point  of  view  of  the  bac- 
terium, as  well  as  from  that  of  the  animal  host, 
according  to  the  hypothesis  advanced,  the  struggle 
between  the  bacteria  and  the  body  cells  in  infec- 
tions may  be  conceived  as  an  immunizing  contest 
in  which  each  participant  is  stimulated  by  its 
opponent  to  the  production  of  cytotoxins  hostile 
to  the  other,  and  thereby  endeavors  to  make  itself 
immune  against  its  antagonist"  (AYelch). 

That  bacteria  may  acquire  increased  resistance 
to  the  destructive  agencies  of  the  host  was  referred 
to  above;  but  the  hypothesis  of  Welch  means  a 
great  deal  more  than  the  immunization  of  the  bac- 
teria against  the  defensive  powers  of  the  animal 
body.  Not  only  may  a  bacterium  during  an  infec- 
tion become  more  resistant  to  the  bactericidal 
action  of  the  body  by  producing  antibodies  to  those 
bactericidal   ao-encies,   or  bv  its   abilitv  to  absorl) 


Immunizing 
Response  by 
Micro- 
orgranisms. 


126  INFECTION    AND    IMMUNITY. 

and  dispose  of  a  greater  quantity  of  bacteriolysiu 
or  ojDsonin ;  and  not  only  may  a  bacterium  be  able 
to  respond  to  the  presence  of  natural  antitoxins  in 
the  body  by  the  production  of  more  toxin,  the 
occurrence  of  which  under  artificial  conditions  was 
shown  by  Wechsberg  in  relation  to  the  diphtheria 
bacillus;  but,  in  addition,  certain  constituents  of 
our  body  fluids  may,  by  combining  with  suitable 
bacterial  receptors,  stimulate  the  bacterium  to  the 
production  of  a  whole  shower  of  cytotoxins,  which 
attack  the  leucocytes,  er3'throcytes,  nerve  cells, 
liver,  kidne}^,  etc.  The  nature  of  the  animal  sub- 
stances which  may  combine  with  the  bacterial 
receptors  and  thus  cause  the  formation  of  the  bac- 
teriogenic  cytotoxins  is  left  an  open  question  and 
is  not  of  essential  importance  to  the  theory;  it  is 
not  at  all  necessary  that  they  be  toxic  to  the  bac- 
terium, and  they  may  even  be  taken  up  as  food 
substances.  Likewise  the  possible  nature  of  the 
cytotoxins  produced  by  the  bacterium  is  of  second- 
ary importance.  It  so  happened  that  Welch 
assumed  that  they  might  be  of  the  nature  of  ambo- 
ceptors which  may  be  complemented  by  bacterial 
complement,  by  the  circulating  complement  of  the 
body  or  by  endocomplements  of  the  tissue  cells. 
One  could  with  equal  reasonableness  assume  that 
they  may  be  complete  toxins,  receptors  of  the  sec- 
ond order,  with  a  haptophorous  and  a  toxophorous 
structure. 

In  some  support  of  this  general  hypothesis  is  the 
observation  that  the  strongest  leucocidin  (a  toxin 
for  leucocytes)  can  be  obtained  from  the  staphylo- 
coccus by  inoculating  this  organism  into  a  serous 
cavity  of  animals,  the  toxin  being  obtained  subse- 
quently from  the  mixture  of  cocci  and  leucocytes. 


ATREPTIG   IMMUNITY.  127 

Investigations  have  not  advanced  far  toward  the 
positive  determination  of  the  correctness  of  the 
hypothesis. 

In  Ehrlich's  conception  of  "atreptic"  immunity, 
the  possibility  is  entertained  that  micro-organisms 
sometimes  may  not  be  able  to  grow  in  a  host 
because  the  nutritive  conditions  are  not  suitable. 
It  probably  would  be  granted  that  proper  nutritive 
substances  are  present  in  the  host/ but  it  is  assumed 
that  they  may  be  so  intimately  and  firmly  bound 
to  other  tissue  constituents  that  they  are  not  avail- 
able to  the  micro-organisms  as  food.  Virulent 
micro-organisms  find  the  nutritive  substances 
already  available,  or,  if  this  is  not  the  condition, 
the  injury  which  they  effect  on  the  tissues  in  the 
first  instance  results  in  a  splitting  of  the  con- 
stituents so  that  the  food  substance  (rather  a  spe- 
cific food  substance)  becomes  available.  Avirulent 
organisms  not  having  the  powxr  to  j)roduce  this 
splitting  result  do  not  proliferate  to  any  great 
degree  and  soon  become  the  prey  of  the  protective 
agencies,  such  as  the  leucocytes  and  bacteriolysins. 
With  this  theory  in  mind,  one  recurs  to  the 
"exhaustion"  theory  of  immunity  at  one  time 
entertained  b}^  Pasteur,  and  cited  in  a  previous 
chapter.  This  difference  appears,  however,  that  in 
Pasteur's  theory  an  entire  absence  of  suitable  food 
was  assumed,  whereas  in  the  atreptic  theory  the 
food  substance  may  be  present  but  not  available  for 
the  use  of  the  organisms.  The  atreptic  theory  is 
put  forward  as  being  a  possible  factor  in  resistance 
to  some  infections  by  some  hosts,  not,  of  course,  as 
a  theory  intended  to  supplant  other  general 
theories  of  immunity. 


PART  TWO 


CHAPTER  VIII. 


TYPES    OF   IMMUNITY. 

By  immunity  we  understand  that  condition  in 
which  an  individual  or  a  species  of  animal  exhib- 
its unusual  or  complete  resistance  to  an  infection 
for  which  other  individuals  or  other  species  show 
a  greater  or  less  degree  of  susceptibility.  Immune 
is  from  the  Latin  immunis,  which  originally  ap- 
plied to  one  who  was  exempt  from  a  public  service, 
exempt  from  tribute,  or  free.  Although  the  word 
retained  this  civil  meaning  for  centuries,  and  still 
retains  it  in  certain  connections,  it  also  had,  even 
in  ancient  times,  a  limited  application  to  the  pro- 
tection which  an  individual  might  possess  against 
poisons.  It  is  seen,  for  example,  in  descriptions 
of  a  tribe  inhabiting  Korthem  Africa,  the  Psylli, 
who  were  said  to  possess  a  natural  immunity  to  the 
bites  of  poisonous  snakes.  Although  we  may  be 
certain  from  this  and  other  references  that  a  con- 
dition of  immunity  was  recognized  in  very  ancient 
times,  the  present  significance  of  the  term  has 
developed  largely  from  a  better  understanding  of 
the  nature  of  infectious  diseases  and  of  the  condi- 
tions upon  which  the  resistance  of  the  body  de- 
pends. 
Diseases       As  the  definition  suo^ffests,  we  do  not  think  of 

Concerned  in    .  .,        ,  -i  -t-»    •    i  j^»        t 

ininninity.  mimuuity  to  sucli  proccsscs  as  Bright  s   disease, 
arteriosclerosis  or  the  metabolic  diseases,  but  only 


NATURAL  IMMUNITY.  129 

to  those  which  we  have  learned  to  recognize  as 
infectious.  The  fact  that  an  individual  is  free 
from  gout,  diabetes  or  any  other  metabolic  disturb- 
ance, cannot  be  taken  as  indicating  an  immunity 
from  these  diseases.  Inasmuch  as  the  metabolic 
diseases  appear  to  depend  on  the  failure  of  certain 
organs  to  perform  their  functions  normalh',  for 
some  one  or  more  reasons,  we  can  only  infer  that 
in  those  who  are  free  from  such  diseases  the  corre- 
sponding organs  are  in  a  state  of  normal  activity. 
Similarly  an  individual  or  race  which  is  free  from 
an  infectious  disease  because  of  lack  of  opportun- 
ity to  contract  it  would  not  be  classed  as  immune. 

Immunity  has  no  necessary  relationship  to  the 
degree  of  contagiousness  of  an  infectious  disease, 
although  some  of  the  most  striking  and  certainly 
the  most  common  examples  of  immunity  are  seen 
in  relation  to  such  infections  (as  scarlet  fever  and 
smallpox).  Tetanus,  on  the  other  hand,  which  is 
absolutely  non-contagious,  can  likewise  give  rise 
to  a  high  degree  of  immunity. 

Xo  medical  fact  is  more  widely  known  among 
intelligent  people  than  that  an  attack  of  certain  immunitx 
of  our  infectious  diseases  brings  about  some  kind 
of  change  in  the  patient's  tissues  which  protects 
him,  or  renders  him  immune,  against  further  at- 
tacks of  the  same  disease.  Inasmuch  as  he  was 
previously  susceptible,  the  new  property  is  an  ac- 
quired one,  and  he  is  now  said  to  possess  an  ac- 
quired immunity  against  this  infection. 

It  is  also  well  known  that  many  diseases  which 
attack  man  can  not  be  inoculated  into  animals, 
and  biologists  are  familiar  with  many  examples 
of  immunity  which  are  confined  to  particular  spe- 
cies.   The  lower  animals  apparently  can  not  be  in- 


Acqulred 


Natural 
Immanlty. 


Imnianity. 


130  IXFECTIOX    AXD    IMMUyiTY. 

fected  with  scarlet  fever  or  measles,  nor  man  with 
chicken  cholera.  The  negro  is  less  susceptible 
than  the  white  man  to  yellow  fever.  The  resist- 
ance which  these  examples  illustrate  exists  natur- 
alty,  not  through  having  the  disease ;  it  is  a  natural 
immunity. 
Family  Sus-  Natural  immunity  is,  for  the  most  part,  an  in- 
and  herited  condition;  this  certainly  is  the  case  where 
a  whole  class  of  animals  is  involved.  Similarly, 
the  susceptibility  which  is  peculiar  to  a  species 
must  be  hereditary.  It  is  often  said  of  some  dis- 
eases that  they  '^'run  in  families ;"  e.  g.,  carcinoma, 
gout,  insanity.  This  appears  to  be  just  as  true  of 
some  infectious  diseases,  the  most  noteworthy  ex- 
ample of  which  is  probably  tuberculosis.  In  con- 
trast to  this  inherited  susceptibility  is  an  inherited 
immunit}^  which  may  also  "run  in  families."  It  is 
not  so  easy  to  adduce  examples  of  this.  We  are  in 
the  habit  of  thinking  of  the  individual  who  can 
resist  all  infections  as  representing  a  standard. 
He,  however,  is  above  the  average  in  resistance, 
and  the  average  is  our  proper  standard  for  esti- 
mating the  resistance  of  a  species  or  race  of  ani- 
mals. It  is  undoubtedly  true  that  some  families 
possess  an  unusual  resistance  to  tuberculosis. 
Furthermore,  experimental  work  with  animals  has 
proved  that,  within  limits,  an  immunity  to  cer- 
tain infections  (e.  g.,  tetanus)  acquired  by  a  fe- 
male may  be  transmitted  to  her  offspring.  Such 
immunit}^,  liowever,  is  very  transient  in  character, 
and  is  "passive"  in  its  type;  it  depends  on  the 
transfer  of  protective  substances  from  the  circula- 
tion of  the  female  parent  to  that  of  the  embryo 
in  utero,  and  some  weeks  after  the  birth  of  the  lat- 
ter these  substances  are  eliminated  and  the  immun- 


ACQUIRED   SUSCEPTIBILITY.  131 

ity  disappears.  That  of  the  parent,  however,  per- 
sists for  a  much  longer  period;  it  is  "active"  in 
character,  as  explained  later.  Even  in  a  given 
family,  however,  there  are  often  marked  variations 
in  susceptibility  and  resistance.  One  child  in  a 
family  may  contract  scarlet  fever,  while  another, 
living  under  exactly  the  same  conditions,  may 
escape  it. 

Susceptibility  also  is  often  acquired  in  a  more 
or  less  evanescent  way.  The  resistance  of  an  indi- 
vidual may  vary  greatly  at  different  times  and 
under  different  conditions.  These  are  accidental, 
acquired  states  such  as  may  be  occasioned  by 
exhaustion,  hunger,  exposure  to  cold  and  other 
unhygienic  conditions. 

Eecently,  the  existence  of  a  specific  acquired  Acquired  sm 
susceptibility  to  various  proteid  substances  and  ^^^ 
bacterial  products  has  been  determined  by  experi- 
mentation. An  injection  of  serum  or  various  pro- 
teids  into  the  proper  animal  renders  it  extremely 
susceptible  to  a  second  injection;  and  a  person 
Avho  is  suffering  from  a  particular  infection  shows 
unusual  sensitiveness  to  the  products  of  the  organ- 
ism causing  the  infection,  as  shown  by  the  tuber- 
culin reaction  of  Koch.  Such  animals  and  indi- 
viduals are  said  to  have  been  sensitized.  This  sub- 
ject will  be  discussed  later  under  "Anaphylaxis." 

Many  of  these  facts  were  familiar  long  before 
anything  was  IvQown  regarding  the  principles  on 
which  they  depend.  Subsequent  to  the  discovery 
of  some  of  these  principles  (to  be  considered 
later),  it  became  convenient  and  necessary  to  rec- 
ognize other  special  types  of  immunity,  although 
any  type  which  can  be  conceived  must  still  find  a 
place  under  either  natural  or  acquired  immunity. 


132 


rXFECTION    AND    HIM  UNITY. 


Antibacterial 
Immunity. 


Phaeocytosls. 


Although  such  diseases  as  t3^phoid  and  cholera 
are  accompanied  by  pronounced  toxic  symptoms, 
the  poisonous  substances  seem  to  be  integrally  as- 
sociated with  the  bacterial  protoplasm  and  not 
secreted  in  a  soluble  or  diffusible  form  by  the  liv- 
ing cell ;  they  are  spoken  of  as  intracellular  toxins 
or  endotoxins.  Observations  point  to  the  belief 
that  the  endotoxins  are  liberated  only  after  the 
bacteria  are  killed  and  dissolved.  When  one, 
through  infection,  has  acquired  immunity  to  ty- 
phoid or  cholera,  his  fresh  serum  is  able  to  kill  the 
respective  bacterium,  but  apparently  is  not  able  to 
neutralize  its  toxic  substance.  Hence,  on  the  basis 
of  the  nature  of  the  serum,  immunity  to  such  dis- 
eases is  spoken  of  as  antibacterial  rather  than 
antitoxic. 

Although  the  subject  is  still  in  a  developmental 
state,  the  conditions  indicate  that  there  are  two 
factors  in  antibacterial  immunity,  one  in  which 
the  plasma  or  serum  has  a  marked  power  of  kill- 
ing the  micro-organisms,  the  other  in  which  the 
destruction  is  largely  by  means  of  "phagocytic  cells. 
The  former  was  just  referred  to.  Both  agencies 
operate  in  many  infections,  as  in  typhoid,  cholera 
and  others;  whereas  in  other  instances  (strepto- 
cocci, staphylococci)  phagocytosis  is  the  only  de- 
tectable protective  agency.  In  most  cases  phago- 
cytosis cannot  take  place  until  certain  constituents 
(opsonins)  in  the  plasma  or  serum  have  "sensi- 
tized" the  bacteria.  In  case  of  recovery  the  power 
of  pliagocytic  destruction  is  usually  enhanced.  We 
have,  therefore,  to  recognize  phagocytic  immunity 
as  a  type,  or  at  least  as  an  important  factor,  in 
botli  n  itural  and  acquired  resistance. 


ANTITOXIC  IMMUNITY.  133 

In  contrast  to  infections  of  the  type  referred  to 
above  are  others  in  which  the  symptoms  are  pro- 
duced by  soluble  toxins,  the  ectotoxins,  which  are 
secreted  by  the  micro-organisms. 

The  symptoms  which  are  so  characteristic  of 
tetanus  are  produced,  not  by  contact  of  the  bacteria 
with  the  nervous  system,  but  rather  through  the 
specific  soluble  toxin  which  is  secreted  by  the  bacilli 
in  the  wound  where  they  reside.  This  poison,  or 
toxin,  is  carried  from  the  wound  to  the  nervous 
system  through  the  lymphatic  or  blood  circulation, 
the  bacterium  itself  not  being  transported.  There- 
fore, although  tetanus  is  a  bacterial  disease,  it  is 
at  the  same  time  and  in  a  peculiar  sense  a  toxic 
disease.  The  serum  of  an  animal  which  has 
acquired  immunity  to  diphtheria  or  tetanus  neu- 
tralizes the  corresponding  soluble  toxin,  but  does 
not  necessarily  injure  the  micro-organism  itself. 
That  is  to  say,  the  immunity  is  antitoxic. 

Experience  has  shown  that  this  distinction 
between  antibacterial  and  antitoxic  immunity  is 
an  important  one,  and  the  differentiation  is  very 
sharp  in  some  instances,  particularly  in  acquired 
immunity.  In  many  examples  of  natural  immun- 
ity, the  resistance  cannot  be  attributed  so  specific- 
ally to  antibacterial  or  antitoxic  serum  properties. 
This  is  referred  to  later. 

In  the  types  of  immunity  referred  to,  the  fac- 
tors on  which  the  resistance  appears  to  depend, 
i.  e.,  the  germicidal  or  antitoxic  action  of  the 
serum  or  the  germicidal  power  of  the  leucocytes, 
are  susceptible  to  experimental  demonstration.  We 
are  familiar  with  another  type  of  resistance,  how- 
ever, which  finds  no  expression  in  the  form  of 
antitoxins  or  other  antibodies.     This  relates  par- 


Antitoxic 

Imiuanity. 


134 


IXFECTION    AND    IMMUNITY. 


Active 
Imniunity. 


Passive 
Immiinity. 


ticularly  to  habituation  to  various  drugs,  as  mor- 
phin,  cocain  or  arsenic,  to  which  a  high  resistance 
may  be  acquired.  The  true  explanation  of  such 
resistance  is  not  known,  but  it  would  appear  to 
depend  on  some  acquired  property  by  the  cells 
which  were  originally  more  susceptible;  in  other 
words,  it  would  appear  to  be  an  immunity  which 
is  fixed  in  the  cells,  a  static  immunity,  so  to  say, 
if  the  expression  may  be  coined.  It  may  depend  on 
habituation  alone,  on  an  increased  power  of  de- 
stroying the  poison  by  the  cells,  or  on  a  decreased 
affinity  of  the  cells  for  the  poison. 

A  similar  process  may  exist  in  acquired  resist- 
ance to  some  of  the  more  chronic  infections,  as 
tuberculosis,  leprosy  and  others,  although  very  lit- 
tle is  known  definitely  concerning  it. 

Immunity  which  results  from  an  infection  de- 
pends on  a  specific  reaction  on  the  part  of  the 
tissue  cells  in  response  to  the  chemical  injury  pro- 
duced by  the  bacteria  or  their  toxins.  The  indica- 
tions of  the  occurrence  of  such  a  reaction  lie,  first, 
in  the  recovery  of  the  patient,  and,  second,  in  the 
new  antitoxic  or  antibacterial  power  which  may  be 
demonstrated  in  the  serum  or  the  increased  phago- 
cytic power  of  his  leucocytes.  In  view  of  the  active 
part  played  by  the  body  in  establishing  this  new 
resistance,  the  condition  is  referred  to  as  an  active 
immunity.  In  the  preparation  of  various  anti- 
toxic and  antibacterial  serums  for  therapeutic  pur- 
poses, a  condition  of  active  immunity  is  deliberate- 
ly produced  in  the  animals  (the  horse,  for  exam- 
ple) by  the  injection  of  the  toxins  or  of  the  bac- 
teria. 

Contrariwise,  the  resistance  which  is  established 
in  an  individual  through  the  injection  of  an  im- 


TYPES   OF  IMMUNITY. 


135 


mune  serum  (such  as  diphtheria  antitoxin)  is  a 
passive  immunity,  since  it  depends  on  the  intro- 
duction of  ready-made  immunizing  substances 
rather  than  on  their  production  through  an  active 
process  on  the  part  of  the  one  injected.  Active 
and  passive  immunity,  then,  are  varieties  of  ac- 
quired immunity.  Depending  on  the  disease 
which  caused  the  immunity,  or  on  the  character 
of  the  serum  injected,  they  may  be  antibacterial 
or  antitoxic,  or,  to  a  certain  extent,  opsonic  (pha- 
gocytic). 

Any  one  of  the  types  mentioned  may  be  either 
relative  (partial)  or  absolute  (complete).  If  the 
immimity  is  absolute,  infection  is  impossible.  If 
only  relative,  different  conditions  may  be  made 
to  prevail  which  would  render  infection  possible; 
for  example,  a  large  number  of  bacteria  will  often 
cause  an  infection  where  a  smaller  number  fails 
to  do  so.  There  may  also  be  a  temporary  decrease 
in  one's  resistance  through  overwork,  hunger  or  ex- 
posure.   Immunity  is  usually  relative. 

By  proper  combinations  of  the  terms  which 
have  been  enumerated,  one  may  describe  somewhat 
accurately  the  different  forms  of  immunity.  Thus, 
a  child  which  has  received  a  prophylactic  injec- 
tion of  diphtheria  antitoxin  is  in  a  state  of  ac- 
quired passive  antitoxic  immunity  to  diphtheria. 
If  immunity  to  typhoid  has  developed  as  a  result 
of  the  disease,  the  condition  is  that  of  an  acquired 
active  antibacterial  immunity,  etc.  Accordingly, 
although  the  terms  may  be  somewhat  confusing, 
it  is  seen  that  they  are  in  no  sense  contradictory. 

The  folloAving  classification  of  the  agencies  which 
may  contribute  to  immunity  in  one  disease  or 
another  may  be  given,  although  we  must  recognize 


Relative  and 

Absolute 

Immunity. 


Classification 
of  Types. 


136  INFECTION    AND    IMMUNITY. 

that  it  probably  does  not  include  all  conceivable 
factors. 

FACTORS   IN  IMMUNITY. 

Natural   Immunity  : 

1.  Antibacterial   properties  of  the  serum   or  plasma. 

2.  Antibacterial  properties  of  the  leucocytes  in  cooperation 

with  opsonins   (preparers  for  phagocytosis). 

3.  Antitoxic  properties  of  the  serum  or  plasma,   resulting 

in  a  simple  binding  or  neutralization  of  toxins. 
Hypothetically,  too,  certain  ferments  of  the  body 
may  split  or  decompose  toxins. 

4.  Total  insusceptibility  of  the  body  to  endotoxins  or  ecto- 

toxins.  Tliere  is  reason  to  believe  also  that  com- 
parative resistance  sometimes  depends  on  the  fact 
that  a  toxin  has  a  stronger  affinity  for  organs  of  less 
vital  importance  for  the  life  of  the  individual  than  it 
has  for  more  important  organs.  The  chicken,  for 
example,  is  very  resistant  to  tetanus,  although  Its 
serum  contains  no  antitoxin.  It  yields,  however, 
when  inoculations  are  made  directly  into  the  nervous 
tissue. 

5.  The   "atreptic"   immunity   of   Ehrlich,   in   which   micro- 

organisms do  not  find  suitable  food,  or  food  in  avail- 
able form,  in  the  body  of  the  host.  This  is  theoreti- 
cal at  present. 

Acquired    Immunity  : 

1.  Increased    antibacterial    properties    of    the    serum     or 

plasma. 

2.  Increased  phagocytic  power  of  the  leucocytes,  and  per- 

haps other  phagocytic  cells,  depending  on  the  increased 
formation  of  opsonins. 

3.  Increased  antitoxic  properties  of  the  serum  or  plasma. 

4.  Habituation  of  the  cells  to  bacterial  poisons. 

Under  3  and  4^  we  may  have  also  to  consider  an 
increased  power  of  splitting  or  digesting  toxic  sub- 
stances. Of  this^  however,  we  know  nothing  defi- 
nite. 

One  and  3  (possibly  also  2)  may  be  passive  as 
well  as  active.  These  subjects  receive  further  con- 
sideration in  subsequent  chapters. 


CHAPTER  IX. 


NATURAL  IMMUNITY. 

Xatural  immunity  to  infection  depends,  first,  on 
certain  obstacles  to  invasion  which  are  afforded 
by  the  body  surfaces  and  the  germicidal  effect  of 
their  secretions;  and,  second,  on  antibacterial  and 
antitoxic  forces  which  are  joresent  in  the  cells  and 
fluids  of  the  interior  body. 

(1)  Protection  Afforded  by  the  Body  Surfaces 

Virulent   organisms    (e.    g.,   staph3dococci   and    The  stin. 

streptococci)  exist  normally  on  the  skin  or  be- 
tween the  superficial  horny  cells,  some  exceptional 
circumstance  being  necessar}^,  e.  g.,  wounds,  to  en- 
able them  to  penetrate  deeper  and  to  cause  disease. 
It  is  evident,  then,  that  the  physiologic  shedding 
of  the  superficial  horny  cells  and  their  continual 
reformation  at  a  deeper  level  is  a  process  calcu- 
lated to  rid  the  surface  of  the  body  of  many  micro- 
organisms. 

The  question  whether  micro-organisms  can  ever 
penetrate  the  unbroken  skin  has  been  much  dis- 
cussed. Although  experiments  have  sho^^Ti  that 
traumatism  is  not  absolutely  necessary,  clinical 
experience  indicates  that  these  so-called  crypto- 
genetic  infections  are  not  of  ready  occurrence. 
When  they  do  occur,  the  infection  atrium  is  prob- 
ably one  of  the  glandular  orifices. 

The  sweat  glands  with  their  ducts,  and  the  hair   Cutaneoas 
follicles    with   their   appended   sebaceous   glands^ 


138  IXFECTION    A^'D    IMMUNITY. 

are  vulnerable  points  in  the  defense  which  the 
cutaneous  surface  represents.  Although  they  are 
protected  somewhat  by  the  flow  of  their  excretions, 
especially  in  warm  weather,  and  although  the  en- 
trance of  germs  is  made  more  difficult  by  the  con- 
traction of  the  skin  and  consequent  narrowing  of 
the  orifices  in  cold  weather,  yet  various  incidents 
may  lead  to  the  introduction  and  retention  of 
virulent  micro-organisms  in  these  structures. 
When  this  occurs  there  is  little  difficulty  in  the 
way  of  their  producing  necrosis  of  the  epithelium, 
invading  the  surrounding  tissue  and  causing  a 
pustule,  boil,  carbuncle,  cellulitis,  or  even  a  gen- 
eralized infection.  The  secretion  of  the  sebaceous 
glands  appears  to  be  not  germicidal.  On  the  other 
hand,  the  acid  nature  and  certain  salts  found  in 
perspiration  render  this  fluid  antagonistic  to  the 
development  and  virulence  of  certain  micro-organ- 
isms. 

The  serous  exudate,  and  the  crust  which  forms 
subsequent  to  an  abrasion,  antagonize  infection. 
The  serum  itself  contains  germicidal  substances, 
while  the  crust  mechanically  prevents  microbic 
invasion. 
sahcQtaneoiis        Solublc  poisons  such  as  aconite  and  bacterial 

Connective  ^ 

Tissue,  toxins  are  not  absorbed  through  the  unbroken  skin. 
Even  after  germs  penetrate  the  epidermis,  the 
subcutaneous  connective  tissue  is  often  an  obstacle 
to  their  further  extension.  The  subcutaneous  in- 
jection of  some  micro-organisms  (e.  g.,  cholera) 
is  tolerated  better  by  animals  than  one  given  into 
the  abdominal  cavity  or  blood  vessels.  We  are 
also  familiar  with  the  benign  course  of  lupus 
compared  with  visceral  tuberculosis;  the  same  is 
true  of  cutaneous  and  visceral  glanders.    This  re- 


MUCOUS    MEM  BR  AXES.  139 

sistance  is  explainable,  at  least  in  part,  by  the 
rapidity  with  which  new  connective  tissue  forms 
in  the  subcutaneous  tissue,  offering  a  mechanical 
limitation  to  the  infection,  and  by  the  rich  lymph 
supply  which  makes  possible  the  rapid  accumula- 
tion of  bactericidal  lymph  and  of  phagocytic  cells. 
On  the  other  hand,  it  must  be  mentioned  that  in 
some  diseases  the  subcutaneous  tissue  offers  no 
perceptible  resistance  to  bacterial  invasion 
(plague),  and  that  toxins  may  be  more  virulent 
when  introduced  into  this  tissue  than  when  in- 
jected into  the  abdominal  cavity  or  the  general 
circulation  (tetanus). 

The  moist  condition  of  mucous  membranes  has  mucous 
been  found  to  favor  the  multiplication  of  many 
microbes,  although  mucus  itself  is  said  to  atten- 
uate the  virulence  of  some  micro-organisms,  as 
the  pneumococcus ;  mucus,  however,  is  not  actively 
germicidal.  A  layer  of  mucus,  on  the  other  hand, 
is  a  mechanical  protection,  and  its  constant  excre- 
tion is  a  means  of  steadily  removing  bacteria  from 
mucous  surfaces. 

The  conjunctiva  is  protected  against  infection  conjunctiTa. 
by  the  mechanical  interference  of  the  eyebrows, 
eyelashes,  eyelids,  irrigation  of  the  conjunctival 
surface  by  tears  which  carry  germs  through  the 
lachrymal  duct  into  the  nasal  cavity,  the  ability 
of  the  conjunctival  epithelium  to  repair  itself 
rapidly,  and  the  mild  germicidal  action  of  the 
salts  which  are  present  in  the  tears.  These  pro- 
tective agencies,  however,  are  often  surmounted 
by  micro-organisms,  such  as  the  pneumococcus, 
staphylococcus  and  the  influenza  bacillus.  Many 
soluble  poisons,  aconite,  diphtheria  toxin  and  the 


140 


IXFECTION    AXD    IMMUNITY. 


toxin  of  hay  fever  are  readily  absorbed  from  the 
conjunctiva. 
Nasal  Cavity.  Compared  with  the  anterior  nares,  the  posterior 
are  poor  in  micro-organisms.  This,  in  part,  at 
least,  is  due  to  the  tortuosity  of  the  channels,  caus- 
ing dust  and  bacteria  to  strike  the  walls  where 
they  are  held  by  a  moist  surface,  and  the  action 
of  the  ciliated  epithelium  in  carrying  them  imbed- 
ded in  mucus,  again  toward  the  anterior  nares. 
Nevertheless,  the  nasal  mucous  membrane  is  a 
common  infection  atrium  for  streptococci,  staph- 
ylococci, diphtheria  and  influenza  bacilli,  the  dip- 
lococcus  of  epidemic  meningitis,  and,  probably,  for 
other  infectious  agents. 
Moutii.  Very  many  species  of  micro-organisms  flour- 
ish in  the  oral  cavity,  some  of  them  being  patho- 
genic :  staphylococci,  streptococci,  pneumococci, 
and  often  diphtheria  bacilli.  They  are  constantly 
removed  with  the  saliva,  and  through  the  exten- 
sive desquamation  of  the  epidermis  occasioned  by 
mastication.  Saliva  is  not  germicidal,  but  in- 
hibits the  growth  and  weakens  the  virulence  of 
some  bacteria.  The  fetid  breath  and  the  sor- 
didity  observed  in  fevers  where  the  mouth  is  dry 
are  attributable  at  least  in  part  to  the  lack  of 
saliva  with  its  anti-infectious  properties.  The 
great  rapidity  with  which  wounds  of  the  month 
bieal  is  a  potent  factor  in  preventing  serious  infec- 
tions. 

^licro-organisms  do  not  readily  reach  the  ulti- 
mate ramifications  of  the  bronchioles.  In  ordinary 
respiration  the  velocity  of  the  inspired  air  is  so 
reduced  as  it  nears  the  alveoli  that  the  further 
movement  of  the  gases  is  one  of  gradual  diffusion 
more  than  of   violent   admixture.      Consequently 


Lnners. 


LUNGS   AND   STOMACH.  141 

there  are  greater  opportunities  for  germs  to  come 
in  contact  with  the  bronchial  walls  where  they 
become  imbedded  in  mucus  with  which  they  may 
be  expelled  by  coughing  and  the  action  of  the 
ciliated  epithelium.  Both  the  alveolar  epithelial 
cells  and  the  leucocytes  which  enter  the  air  sacs 
and  bronchioles  have  been  shown  to  take  up  bac- 
teria. The  conditions  in  the  lungs  which  favor 
the  development  of  infections,  as  bronchitis,  pneu- 
monia, influenza,  tuberculosis,  are  by  no  means 
clearly  understood.  Variations  in  individual 
resistance,  here  as  in  other  parts  of  the  body,  such 
as  may  be  caused  by  exposure  to  cold,  are  certainly 
of  great  importance.  It  is  probable  that  the  lung 
is  the  infection  atrium  for  a  number  of  our  acute 
infectious  diseases.  It  has  been  demonstrated  that 
systemic  infections,  as  with  anthrax  bacilli,  may 
be  caused  by  the  inhalation  of  the  micro-organisms. 

The  gastric  juice,  through  the  hydrochloric  stomach. 
acid  it  contains,  is  able  to  kill  anthrax,  typhoid, 
tubercle  bacilli,  cholera  vibrio  and  other  organ- 
isms. Clinical  and  experimental  evidence  shows 
that  this  power  is  often  inadequate,  virulent 
micro-organisms  reaching  the  intestines  in  spite 
of  it  (typhoid,  cholera,  dysentery,  tuberculosis, 
etc.).  It  is  probable  that  bacteria  in  the  stomach 
are  often  protected  against  the  action  of  the  gas- 
tric juice  to  some  extent  by  being  imbedded  in 
solid  particles  of  food.  Certain  acidophilic  germs, 
as  well  as  yeasts  and  torulse,  seem  to  flourish  in  the 
gastric  secretions;  these  are  largely  non-patho- 
genic, but  the  regularity  with  which  peritonitis 
follows  perforating  wounds  of  the  stomach  indi- 
cates that  it  probably  always  contains  pathogenic 
bacteria,  though  it  may  be  only  their  temporary 


142  IXFECTIO^'    AXD    IMMUXITY. 

habitat.  The  gastric  juice  may  render  some  bac- 
teria harmless  by  digesting  their  toxins;  one 
gram  of  the  gastric  juice  of  a  dog  will  neutralize 
fifty  fatal  doses  of  diphtheria  toxin,  or  10,000  of 
tetanus  toxin,  using  the  guinea-pig  as  the  test 
animal.  On  the  other  hand,  the  toxin  of  the  bacil- 
lus of  botulism  (causing  a  form  of  meat  poison- 
ing) seems  to  be  uninfluenced  by  the  stomach  con- 
tents, as  the  development  of  the  intoxication  indi- 
cates. Vomiting  is  often  a  means  of  ridding  the 
stomach  of  toxic  substances,  including  bacteria. 
The  stomach  itself  is  exceptionally  free  from  in- 
fections. 
Intestines.  The  bile  Is  moderately  bactericidal  for  some 
germs,  but,  on  the  whole,  the  intestinal  secretions 
have  low  germicidal  powers;  this  is  indicated  by 
the  fact  that  the  colon  contains  many  more  bac- 
teria than  the  duodenum.  On  the  other  hand, 
the  pancreatic  juice  destroys  some  toxins  (diph- 
theria, tetanus)  more  powerfully  even  than  the 
gastric  juice.  This  ability  of  the  pancreatic  juice 
(o  destroy  toxic  bacterial  products  may  explain  the 
more  frequent  occurrence  of  enteritis  in  the  ileum 
than  in  the  duodenum.  The  bile  also  has  a  neu- 
tralizing power  for  some  toxins.  Although  a  num- 
ber of  pathogenic  bacteria  inhabit  the  intestinal 
tract  (colon  bacillus,  streptococci,  etc.),  they  do 
not  often  set  up  inflammatory  processes  in  the 
adult.  The  tissues  become  accustomed  to  their 
presence.  The  pathogenic  bacteria  which  do  not 
normally  exist  in  the  intestines  are  those  which, 
on  introduction,  are  most  likely  to  cause  disease 
(typhoid,  cholera,  dysentery,  etc.).  The  intesti- 
nal tract  of  the  infant,  on  the  other  hand,  is  fre- 
quently attacked  by  some  micro-organisms  (strep- 


INFLAMMATION.  143 

tococcus,  colon  bacillus^  Bacillus  pyocyaneus) , 
which  in  the  same  locality  in  the  adult-  appear 
harmless.  The  fact  that  many  individuals  are  not 
stricken  in  an  epidemic,  in  which  all  are  equally 
exposed  to  infection,  points  to  the  probability  that 
pathogenic  organisms  (typhoid,  cholera  and  dys- 
entery) often  traverse  the  intestinal  canal  without 
inducing  disease.  Naturally,  microbes  are  elimi- 
nated in  enormous  quantities  in  the  feces,  and  in 
inflammatory  states  this  elimination  is  increased 
by  diarrhea.  It  is  also  not  to  be  forgotten  that  the 
intestinal  tract  is,  to  a  considerable  extent,  a 
lymphoid  organ,  and  that  in  the  presence  of  infec- 
tion enormous  quantities  of  phagocytes  can  be 
called  into  action  quickly. 

The  protective  properties  of  the  genito-urinary 
surfaces  are  not  different  in  principle  from  those 
already  mentioned  (vaginal  acidity,  mechanical 
and  perhajDS  bactericidal  cleansing  by  the  men- 
strual flow,  urinary  irrigation). 

(2)  Internal  Protective  Agencies. 
A.  Inflammation. 

Although  there  are  many  chemical  and  physical 
agents  which  may  cause  inflammation,  we  are  in- 
terested here  only  in  those  of  an  infectious  na- 
ture. 

Inflammation  may  be  considered  as  a  reactive  Nature  of 
condition  on  the  part  of  the  tissues,  which  devel- 
ops in  response  to  the  action  of  some  injurious 
agent.  The  process  may  be  beneficial  in  some  in- 
stances, while  in  others  it  may  be  pernicious  from 
the  beginning  to  the  end.  The  thickening  of  the 
endothelium  of  the  cerebral  vessels  as  one  sees  it 
in  syphilis  is  a  progressive,  reactive  change  which 


Inflamiuatioii. 


144  nFEGTION    AXD    IMMUNITY. 

in  no  sense  can  be  of  benefit  to  the  individual,  and 
which  can  have  no  conceivable  function  in  over- 
coming the  syphilitic  infection.  Likewise,  the  new- 
formed  connective  tissue  seen  in  alcoholic  cirrho- 
sis of  the  liver  is  of  no  benefit  to  the  hepatic  tissue, 
though  it  may  serve  in  some  degree  to  protect  the 
liver  cells  from  the  alcohol  which  continues  to  be 
ingested.  In  an  ulcer  of  the  cornea  the  presence 
of  serum  and  of  leucocytes,  as  well  as  the  prolifer- 
ation of  connective  tissue,  may  be  the  sine  qua  non 
for  the  healing  of  the  ulcer,  yet  the  resulting  scar 
may  greatly  impair  the  vision.  The  inflammation 
in  the  instance?  cited  is  injurious  because  of  the 
functional  importance  of  the  tissues  involved.  On 
the  other  hand,  an  extensive  scar  which  has 
formed  in  tissues  of  less  functional  importance, 
as  in  the  skin  and  subcutaneous  tissue,  may  be 
harmless. 

It  is,  then,  to  be  recognized  that  there  are  certain 
consequences  of  the  inflammatory  reaction,  the 
seriousness  of  which  depends  on  the  situation, 
severity,  duration  and  extent  of  the  process,  and 
that  these  consequences  are  independent  of  any 
protective  function  the  inflammation  may  have 
exercised. 
Variations        The  amouut  and  character  of  the  reaction  are 

la  Reactions.  ,  .      ,     ,  •    ,.  -,  t 

subject  to  many  variations,  depending  on  a  num- 
ber of  conditions: 

1.  It  varies  with  the  nature  of  the  microbe. 
Non-pathogenic  organisms  induce  little  more  in- 
flammation than  so  many  minute,  inanimate, 
non-toxic  particles.  The  tubercle  bacillus  causes 
especially  the  formation  of  connective  tissue, 
giant  cells  and  the  accumulation  of  lymphoid 
cells,  aside  from  some  retrogressive  changes  char- 


LEUCOCYTES.  145 

acteristic  of  the  disease.  Organisms  similar  to 
the  streptococcus  and  pneumococcns  lead  to  the 
formation  of  pus  and  fibrin,  to  the  accumulation 
of  serum  and  of  polymorphonuclear  leucocytes 
more  than  mononuclears,  whereas  the  prolifera- 
tion of  fixed  tissue  elements  is  secondary.  The 
tetanus  bacillus  alone  causes  almost  no  local  in- 
flammatory change. 

2.  The  reaction  is  influenced  by  the  virulence 
of  a  particular  strain.  A  streptococcus  which 
has  lost  its  virulence  is  disposed  of  by  the  animal 
tissues  with  a  minimum  tissue  reaction,  perhaps 
no  more  than  slight  congestion  and  edema  and 
the  wandering  in  of  a  few  leucocytes ;  one  of  high- 
er virulence  causes  an  intense  reaction,  mani- 
fested by  congestion,  edema,  hemorrhages,  necro- 
sis and  pus  formation;  then  streptococci  of  such 
great  virulence  that  they  destroy  life  in  the  course 
of  a  few  hours  are  occasionally  encountered  in 
wound  infections  and  in  peritonitis,  having  in  the 
meantime  elicited  a  minimum  inflammatory  reac- 
tion. 

3.  It  has  a  relation  to  the  resistance  or  the  nat- 
ural immunity  of  the  individual.  Metchnikoif, 
in  particular,  has  shown  that  animals  of  high  re- 
sistance to  a  particular  microbe  destroy  the  germ 
quickly  by  phagocytosis,  while  in  susceptible  ani- 
mals the  accumulation  and  activity  of  phagocytic 
leucocytes  are  deficient. 

The  occurrence  of  leucocytes  in  inflammatory  Leucocytes. 
conditions  is  so  characteristic  that  one  naturally 
seeks  to  associate  their  presence  with  some  in- 
fluence which  is  exerted  by  the  toxic  substance  or 
the  bacteria  which  cause  the  inflammation.  It  is 
a  long-known  fact  that  some  microbes  attract  one 


146  INFECTION    AND    IMMUNITY. 

kind  of  leucocytej  that  others  attract  another 
kind,  and  that  in  still  other  instances  the  leuco- 
cytes appear  to  be  either  uninfluenced  or  actually 
are  repelled  by  the  infecting  agent. 
chemotaxis.  The  phenomenon  of  living  cells  moving  toward 
or  away  from  certain  other  cells  or  substances  is 
an  expression  of  affinity  and  this  affinity  is  known 
as  chemotaxis;  the  former  is  positive,  the  lat- 
ter negative,  chemotaxis.  There  is  a  somewhat 
general  law,  but  one  to  which  exceptions  exist. 
that,  regardless  of  the  microbe  involved,  the  more 
acute  the  inflammatory  process  the  more  do  poly- 
morphonuclear leucocytes  accumulate,  while  in 
the  more  chronic  infections,  with  much  connec- 
tive tissue  formation,  the  mononuclear  leucocytes 
predominate.  Thus  in  tuberculosis  one  finds 
lymphocytes  and  plasma  cells — mononuclears — 
predominating  greatly  over  the  polymorphonu- 
clears. In  the  acute  purulent  infections,  on  the 
other  hand — streptococcus,  staphylococcus,  pneu- 
mococcus — the  latter  type  of  leucocyte  predomi- 
nates, the  mononuclears  being  fewer  and  remain- 
ing at  a  distance  from  the  center  of  action.  There 
is  reason  to  believe  that  the  mononuclear  leuco- 
cytes play  an  important,  though  perhaps  indirect, 
role  in  the  formation  of  the  connective  tissue. 
piiagocytosis.  The  ingestion  of  particles  by  living  cells,  phago- 
cytosis, is  a  property  which  many  cells  possess. 
Although  micro-organisms  and  inanimate  parti- 
cles are  sometimes  found  in  epithelial  cells,  cer- 
tain of  the  mesoblastic  cells  have  this  function 
pre-eminently :  polymorphonuclear  leucocytes,  large 
mononuclear  leucocytes  (lymphocytes),  ameboid 
connective  tissue  and  endothelial  cells.  Of  these 
the  polymorphonuclear  leucocytes,  the  microphages 


PLASMA    AND    SERUM.  147 

of  Metchnikoff,  have  the  greatest  phagocytic  power ; 
the  others,  the  macrophages,  are  more  exception- 
ally phagocytic,  but  some  of  them  take  up  such 
cells  as  erythrocytes  and  other  tissue  cells  readily. 
Now,  the  mere  ingestion  of  the  bacteria  by  such 
cells  would  not  be  of  necessity  injurious  to  the 
microbes;  indeed,  opponents  of  Metchnikoff's  pha- 
gocytic theory  of  immunity  held  that  phagocytosis 
by  wandering  cells  may  be^  and  often  is,  pernicious, 
in  that  the  cells  may  return  to  the  circulation  and 
spread  the  infection  to  other  parts.  This  is  prob- 
ably true  in  many  instances.  But  when  we 
learn  that  after  ingesting  the  bacteria  the  phago- 
cytes are  often  able  to  kill  and  digest  them,  it  is 
realized  that  the  process  may  be  a  genuine  pro- 
tective factor.  This  being  true,  the  importance  of 
positive  chemotaxis  in  recovery  from  an  infection 
becomes  manifest.  It  is  also  represented  that 
phagocytic  cells  have  the  power  of  excreting  their 
germicidal  substances  into  the  plasma  and  serum 
and  lending  to  the  latter  a  bactericidal  power. 
Furthermore,  it  is  held  that  they  may  absorb  liquid 
poisons,  bacterial  toxins,  and  in  some  manner  de- 
stroy their  toxicity.  As  shown  later,  these  are  es- 
sential points  in  the  phagocytic  theory  of  immun- 
ity. 

Serum,  even  when  entirely  free  of  leucocytes, 
has  bactericidal  powers  for  many  micro-organisms ; 
it  need  not  be  discussed  at  present  whether  this 
power  exists  primarily  in  the  serum  or  is  one  con- 
ferred on  it  by  the  leucocytes.  In  view  of  its  pres- 
ence, however,  it  is  evident  that  the  serous  exu- 
date which  is  usually  present  in  inflammations, 
especially  the  acute,  may  be  of  influence  in  com- 
bating the  infection.     Serum  mav  contain  natural 


Influence  of 
Plasma  and 
Semm. 


148  IXFECTION    AXD    IMMUNITY. 

antitoxins,  and,  in  addition,  it  ma}^  be  of  value 
in  lessening  the  toxicity  of  poisons  by  diluting 
them,  aiding  in  their  elimination,  or  destroying 
them  by  means  of  ferments  (!). 
Fibrin.  The  abundant  deposit  of  fibrin  seen  in  some  in- 
flammations is  of  mechanical  value  by  hemming 
in  the  infection  and  by  offering  a  barrier  to  the 
rapid  diffusion  of  toxins.  We  are  all  familiar 
with  the  part  played  by  fibrinous  and  fibrous  ad- 
hesions in  preventing  a  localized  peritonitis  from 
becoming  generalized.  In  prolonged  inflamma- 
tions fibrin  furnishes  a  ground  substance  into 
which  new  connective  tissue  and  vessels  grow  (or- 
ganization) . 
[nflammatory        ^j^g  new-fomicd  conncctive  tissue  seen  in  many 

Connective  ^  ,  .  '^ 

Tissue,  inflammations,  especially  the  chronic,  as  in  tuber- 
culosis and  actinomycosis,  offers  an  important 
barrier  to  the  extension  of  an  infection.  Perhaps 
no  better  example  of  this  could  be  cited  than  the 
dense  tissue  which  forms  around  a  tuberculous 
sinus  or  abscess. 

To  sum  up,  the  inflammatory  reaction  antago- 
nizes infections,  (1)  mechanicall}^,  through  the 
formation  of  new  connective  tissue  around  the 
focus,  and  dense  accumulations  of  leucocytes  and 
fibrin;  (2)  through  the  bactericidal  and  antitoxic 
actions  of  the  lymph  and  serum;  (3)  through  the 
phagocA^ic  action  of  ameboid  cells. 

The  value  of  hot  applications,  and  Biers  passive 
congestion  treatment,  in  local  inflammations,  finds 
a  logical  explanation  in  view  of  the  facts  men- 
tioned, in  that  they  increase  congestion,  which 
hastens  the  exudation  of  plasma  and  leucocytes 
and  the  proliferation  of  cells,  and  accelerate  the 
elimination  of  toxic  substances. 


NATURAL   IMMUNITY. 


149 


Natural 
Immanity. 


The  special  features  of  the  phagocytic  theory  of 
immunity  are  considered  in  a  later  chapter.  For 
many  details  in  regard  to  inflammation,  the  reader 
is  referred  to  the  classic  article  of  Adami  on  this 
subject  in  the  first  volume  of  Allbutt's  "System  of 
Medicine/^ 

B.  Properties  of  the  Serum  and  Plasma. 

We  have  seen  that  the  protection  afforded  by 
the  body  surfaces  may  be  effective  against  both 
microbes  and  their  toxins,  and  that  local  inflam- 
matory processes,  although  most  certainly  antago- 
nizing  the  bacteria,  may  at  the  same  time  have 
some  antitoxic  value. 

The  term  "natural  immunity,"  however,  as  indi- 
cated in  the  preceding  chapter,  has  a  peculiar  appli- 
cation to  the  natural  resistance  of  some  species  or 
races  of  animals  to  infections  to  which  other  spe- 
cies or  races  are  susceptible ;  and  to  an  unusual  in- 
dividual resistance  often  seen  in  members  of  a 
given  race  or  species.  This  condition  depends  on 
properties  residing  in  the  tissues  or  fluids  of  the 
body,  and  consequently  is  independent  of  any  pro- 
tection which  the  body  surfaces  afford.  Its  pres- 
ence is  demonstrated  in  the  most  striking  man- 
ner by  the  experimental  method,  when  micro-or- 
ganisms or  toxins  are  injected  directly  into  the  tis- 
sues or  circulation.  At  the  same  time  every-day 
obs'fervation  provides  many  examples. 

In  certain  instances  natural  immunity  or  sus-  zooiogricai 
ceptibility  shows  a  relation  to  zoological  affinities. 
Thus  only  man  and  the  higher  apes  are  susceptible 
to  syphilis;  and  only  animals  which  are  closely 
related  to  cattle,  as  sheep^  goats  and  other  rumi- 
nants,  suffer  from  rinderpest.     There   are  many 


Relation' 
ships. 


150  IXFECTIOy    AXD    IMMUXITY. 

exceptions  to  this  tendency,  however;  perhaps  the 
most  striking  example  is  found  in  the  fact  that 
whereas  sheep  ordinarily  are  extremely  susceptible 
to  anthrax^  Algerian  sheep  are  relatively  immune. 
Similarly  the  white  rat  is  immune  (relatively) 
and  the  wild  rat  is  susceptible  to  anthrax. 
Factors  in  Xatural  immunity  may  depend  on  a  lack  of 
Immunity,  pathogenicity  on  the  part  of  the  organism  for  the 
host,  which  is  equivalent  to  insusceptibility  on  the 
part  of  the  host;  or,  on  the  presence  in  the  host 
of  a  sufficient  quantity  of  antibacterial  and  anti- 
toxic substances;  or,  as  suggested  by  Ehrlich,  on 
the  inability  of  the  micro-organism  to  proliferate 
in  the  host  because  proper  nutritive  substances  are 
not  present,  or,  if  present,  are  bound  to  other  sub- 
stances in  such  a  way  that  they  are  not  available  as 
food  for  the  organisms. 

As  stated  in  the  preceding  chapter,  immunity 
may  be  either  antibacterial  or  antitoxic,  i.  e.,  the 
immunity  may  in  one  case  depend  on  the  power 
of  the  animal's  tissues  and  fluids  to  destroy  the 
micro-organisms,  or,  in  another,  on  their  power 
to  neutralize  or  destroy  the  bacterial  toxins. 

The  distinction  between  antibacterial  and  anti- 
toxic immunity  is  demonstrated  more  readily  in 
acquired  than  in  natural  immunity.  When  one 
has  recovered  from  typhoid  fever,  for  example,  his 
serum  has  acquired  an  increased  power  of  killing 
the  typhoid  bacillus,  while  at  the  same  time  it 
appears  to  have  little  or  no  power  of  neutralizing 
tlie  poisons  of  this  organism.  Acquired  immunity 
to  diphtheria,  on  the  other  hand,  is  characterized 
by  the  power  of  the  serum  to  neutralize  the  toxin 
of    the    diphtheria    bacillus,    although    it    hardly 


TYPES   OF  IMMUNITY.  151 

exceeds  normal  serum  in  its  bactericidal  power  for 
the  bacillus  itself. 

Having  ascertained  by  observation  or  experi-  ^j^^^^'JJ****'' 
ment  that  a  certain  species  has  a  degree  of  immun-  Types  of 
ity  to  an  infection,  certain  lines  of  investigation 
may  be  followed  for  the  purpose  of  determining 
the  character  of  the  immunity.  If  the  animal 
fails  to  become  infected  following  the  injection 
of  a  living  and  virulent  culture,  it  is  fair  to  assume 
that  the  organisms  have  been  killed  within  the 
body  of  the  animal.  That  this  has  been  the  result 
ma}^,  indeed,  be  determined  by  microscopic  exam- 
ination of  the  different  tissues  and  by  the  inocula- 
tion of  culture  media.  It  is  often  desirable  to 
determine  the  extent  to  which  micro-organisms 
are  eliminated  through  the  excretions  (urine  and 
feces)  ;  this  is  best  done  by  the  culture  method, 
but  it  is  often  a  difficult  technical  problem. 

The  natural  antibacterial  forces  with  which  we 
are  familiar  consist  of  the  germicidal  action  of 
the  serum  and  plasma,  and  the  phagocytic  and 
destructive  action  of  the  leucocytes,  endothelial  and 
perhaps  other  cells.  It  is  difficult  to  obtain  sat- 
isfactory results  by  a  study  of  these  forces  within 
the  body  of  the  animal,  particularly  as  regards  the 
bactericidal  action  of  the  serum  and  plasma,  hence 
such  studies  are  usually  carried  on  outside  the 
body.  Such  experiments  are  open  to  the  criticism, 
however,  that  the  artificial  conditions  are  far 
removed  from  those  of  the  body,  and  that  the 
results  do  not  always  justify  us  in  drawing  con- 
clusions reo^ardins:  the  course  of  events  within  the 
body.  Phagocytosis  under  natural  conditions  is 
more  susceptible  to  study,  and  it  is  to  be  remem- 
bered that  Metchnikoff  came  to  his  far-reaching 


152  INFECTION    AXD    IMMUXITY. 

conclusions  regarding  the  importance  of  phagocy- 
tosis purely  from  a  study  of  the  process  in  vivo.  In 
spite  of  this  we  have  come  to  a  better  understand- 
ing of  the  mechanism  of  phagocytosis  by  studies 
of  the  phenomenon  under  artificial  conditions,  as 
will  appear  later. 
Germicidal  In  determining  the  germicidal  action  of  serum, 
Serum,  wliich  sliould  be  freshly  obtained,  it  may  be 
mixed  with  a  suspension  of  the  microbes  in  a 
number  of  test-tubes,  varying  amounts  of  serum 
being  used  with  constant  amounts  of  the  bacteria 
in  the  different  tubes.  At  a  subsequent  period, 
from  three  to  twenty-four  hours  later,  cultures  on 
Petri  plates  are  made  from  these  mixtures.  The 
numbers  of  colonies  which  appear  in  these  cultures, 
compared  with  the  number  which  appear  when 
serum  is  not  added,  is  an  index  of  the  bactericidal 
power  of  the  serum.  If  this  power  is  found  to  be 
high,  it  is,  in  the  present  state  of  our  knowledge, 
considered  as  presumptive  evidence  that  the  nat- 
ural immunity  of  the  animal  depends  on  it,  at 
least  in  part.  It  is,  nevertheless,  a  fact  that  the 
antibacterial  immunity  of  an  animal  does  not 
always  go  hand  in  hand  with  the  bactericidal  power 
of  its  serum.  A  well-known  illustration  of  this  is 
the  following :  Both  the  dog  and  the  rat  have  a 
rather  high  degree  of  immunity  against  infections 
with  the  anthrax  bacillus;  yet  it  has  been  found 
that  the  serum  of  the  dog  has  almost  no  bacteri- 
cidal effect  on  this  microbe,  while  that  of  the  rat 
has  a  very  strong  effect.  At  the  same  time  we 
should  remember  that  the  bactericidal  power  of  the 
serum  does  not  necessarily  represent  the  entire 
antibacterial  function  of  the  body.  In  the  serum 
we  have  none  of  the  body  cells,  and  especially  none 


OPSONIN  IS.  153 

of  the  phagocytes,  the  destructive  action  of  which 
on  some  bacteria  is  well  known.  Many  micro- 
organisms, indeed,  which  are  not  destroyed  by 
serum  at  all,  are  readily  ingested  and  killed  by 
leucocytes  (staphylococci,  streptococci). 

As  a  consequence  of  fundamental  studies  by  Phagocytosis 
Denys  and  Le  Clef,  by  Leishman,  by  A.  E.  Wright 
and  others,  it  is  now  possible  to  study  phagocytosis 
in  vitro  with  a  degree  of-  accuracy  not  to  be  approx- 
imated in  the  living  body.  It  has  been  learned  that 
leucocytes,  as  a  rule,  are  not  able  to  take  up  bac- 
teria until  the  latter  have  been  acted  on  (sensi- 
tized) by  some  substance  which  is  contained  in  the 
serum.  Wright  gave  the  name  of  "opsonins"  to 
these  substances.  Some  of  them  are  susceptible  to 
heat  (55  C),  while  others  are  much  more  resist- 
ant. To  the  latter^  which  are  greatly  increased  by 
infection  or  artificial  immunization,  Neufeld  has 
applied  the  term  "bacteriotropins.'^ 

Leishman's  method  is  to  mix  a  suspension  of 
the  bacteria  with  defibrinated  blood  (containing 
leucocytes),  incubate  the  mixture  for  fifteen  or 
more  minutes,  to  make  and  stain  spread  prepara- 
tions on  slides,  and  then  count  the  number  of  bac- 
teria which  have  been  ingested  by  the  leucocytes. 
The  average  number  taken  up  by  fifty  or  more  leu- 
cocytes constitutes  the  "phagocytic  index."  AYright 
has  varied  this  technic  in  order  to  study  the  opson- 
ins quantitatively,  as  will  be  described  later. 

Experiments  have  shown  that  all  normal  serums 
contain  opsonins  for  a  variety  of  micro-organisms, 
and  all  micro-organisms  are  susceptible  to  phagocy- 
tosis by  the  blood  of  one  or  more  animals,  in  case 
their  virulence  is  not  excessive.  We  have  every 
reason,  therefore,  to  believe  that  phagocytosis  is 


154 


INFECTION    AND    IMMUNITY 


Alexins. 


Nataral 

Antitoxic 

Inininnity. 


an  important  natural  protective  factor,  and  in 
some  instances  it  is  the  onl}'  one  which  can  be 
actually  demonstrated,  as  in  the  case  of  staphylo- 
cocci and  streptococci. 

That  organisms  are  often  destroyed  after  being 
ingested  by  the  leucocytes  is  manifest  from  changes 
in  form  which  they  undergo,  and  from  the  loss  of 
their  staining  power.  Cultivation  experiments 
have  also  shown  that  the  leucocytes  are  able  to 
kill  certain  bacteria.  In  such  experiments,  the 
technic  which  was  mentioned  in  testing  the  bac- 
tericidal power  of  serum  may  be  used,  in  this  case, 
however,  substituting  defibrinated  blood,  which 
contains  leucocytes,  in  place  of  the  serum.  If  the 
bactericidal  power  of  the  defibrinated  blood  is 
greater  than  that  of  the  serum  alone,  the  effect  of 
the  leucocytes  becomes  apparent. 

At  a  time  when  the  antitoxic  action  of  serums 
was  not  appreciated,  Buchner  gave  the  name  of 
alexins  (from  the  Greek,  dU^eiv ^  to  ward  off)  to 
the  protective  substances  of  the  serum,  i.  e.,  to  the 
bactericidal  substances,  making  the  observation 
that  they  were  very  labile  substances,  losing  their 
power  spontaneously  in  a  few  days  when  exposed 
to  the  air  and  light,  or  when  they  were  heated  at 
55  C.  for  thirty  minutes.  As  will  be  indicated 
later,  the  "alexins"  are  more  complex  than  Buchner 
supposed. 

In  determining  the  presence  or  absence  of  anti- 
toxic immunity,  the  toxin  of  the  microbe,  of 
course,  must  first  be  in  hand.  The  methods  of  ob- 
taining toxins  will  be  referred  to  later.  If  the 
animal  resists  a  dose  of  toxin  which,  in  proportion 
to  weight,  produces  disease  in  some  other  suscepti- 
ble animal,  the  tissues  or  fluids  of  the  first  animal 


ANTITOXIC   IMMUNITY.  155 

may,  or  may  not,  contain  antitoxin.  If  the  resist- 
ance is  referable  to  the  presence  of  antitoxin^  the 
latter  may  be  detected  in  the  following  manner: 
The  animal  is  bled,  its  serum  collected  from  the 
clot,  then  mixtures  of  the  serum  and  of  the  toxin 
are  injected  into  animals  of  loiown  susceptibility 
for  the  toxin.  If  the  test  animal  is  in  this  way 
protected  from  an  otherwise  fatal  dose  of  the  toxin, 
it  is  evidence  that  the  serum  contains  an  antitoxic 
substance.  On  the  other  hand,  if  the  serum  shows 
no  such  antitoxic  effect,  we  must  conclude  that  the 
resistance  of  the  animal  is  due  to  other  causes;  as, 
for  example,  non-susceptibility  of  the  tissues, 
power  of  the  living  cells  or  ferments  to  destroy  the 
toxin,  or  absorption  of  the  toxin  by  tissues  of  sec- 
ondary importance  to  life. 

Following  this  method  of  experimentation,  if 
antibacterial  properties  are  found  to  the  exclusion 
of  antitoxic,  the  immunity  is  considered  to  be  an- 
tibacterial; and  with  the  converse  result  it  is  anti- 
toxic, or  dependent  on  non-susceptibility.  It  is,  of 
course,  conceivable  that  in  a  given  case  it  might  be 
both  antitoxic  and  antibacterial.  In  dealing  with 
diseases  of  which  the  specific  microbe  is  known 
and  cultivated,  the  existence  of  antibacterial  or  of 
antitoxic  substances  can  usually  be  found  by  the 
methods  described.  If  the  etiology  is  unknown,  or 
the  micro-organism  cannot  be  cultivated,  as  in 
scarlet  fever,  measles,  etc.,  that  is,  if  the  virus  and 
its  toxin  cannot  be  obtained  in  quantities,  the 
nature  of  the  resistance  is  not  at  present  open  to 
determination. 

It  is  seldom  that  natural  resistance  is  absolute. 
Pasteur  found  that  the  great  immunity  of  the 
chicken  for  anthrax   could  be  overcome  by  im- 


156  IXFECTlOy    AXD    IMilUXITY. 

mersing  the  animal  in  cold  water,  the  reduction 
in  body  temperature  supposedly  decreasing  the  re- 
sistance. It  was  stated  previously  that  physical 
exhaustion,  hunger  and  exposure  to  cold  may  also 
reduce  natural  resistance.  Pestilence  and  famine 
often  go  hand  in  hand. 
_  Relative  Similarly,  immunity  to  toxins  usually  is  rela- 
tive. As  an  illustration  of  natural  immunity  to 
toxins,  the  following  table  serves  a  good  purpose. 
The  horse  is  the  animal  of  greatest  susceptibility 
to  tetanus  toxin.  If  the  minimum  fatal  amount  of 
one  gram  of  horse  weight  is  taken  as  a  unit,  this 
scale  of  resistance  for  some  other  animals  is 
obtained   (Knorr)  : 

For  1  gram  of  guinea-pig  weight 2  units  ai"e  fatal 

For  1  gram  of  goat  weight 4  units  are  fatal 

For  1  gram  of  mouse  weight 13  units  are  fatal 

For  1  gram  of  rabbit  weight 2,000  units  are  fata 

For  1  gram  of  chicken  weight 200,000  units  are  fatal 

xon-snscep-  ^^  ^'i^w  of  the  high  immunity  of  the  chicken 
tibiiity.  agaiust  tetanus,  one  may  be  led  to  suppose  that  its 
serum  would  contain  a  large  amount  of  antitoxin, 
yet  experiments  show  that  it  possesses  practically 
no  tetanus  antitoxin.  This  fact  suggests  that 
there  is  a  distinct  type  of  natural  immunity 
which,  it  is  thought,  may  be  independent  of  both 
the  antibacterial  and  the  antitoxic  properties  of 
the  body. 
Cell  It  is  now  thought  that  the  toxic  elements  of  bac- 
teria are  chemical  substances  (very  complex, 
surely)  which  are  able  to  injure  the  tissues,  i.  e., 
to  cause  disease,  only  by  entering  into  chemical 
union  with  substances  which  the  cells  contain. 
Such  chemical  substances  or  groups,  pertaining 
to  the  cells,  will  be  referred  to  later  under  the 
name  of  cell  receptors.     Accordingly,  if  the  cells 


CELL  RECEPTORS.  157 

of  an  animal  do  not  possess  groups  or  receptors 
which  are  capable  of  forming  a  chemical  union 
with  the  toxin,  the  latter  would  be  unable  to  pro- 
duce injury,  i.  e.,  the  animal  would  be  immune 
even  in  the  absence  of  ail  bactericidal  or  antitoxic 
properties.  This  condition,  however,  is  not  one 
which  is  capable  of  satisfactory  demonstration, 
at  least  at  present,  but  the  conditions  point  irre- 
sistibly to  its  existence  in  some  cases. 

We  are  accordingly  led  to  the  conclusion  that 
immunity  to  toxins  is  not  in  all  cases  antitoxic, 
in  the  sense  that  the  serum  contains  demonstrable 
antitoxin;  and  likewise  that  immunity  to  bacteria 
is  not  in  all  cases  antibacterial,  in  the  sense  that 
the  serum  contains  substances  which  are  able  to 
kill  the  bacteria  in  test-tube  experiments.  Non- 
susceptibility  and  phagocytosis  may  be  of  impor- 
tance in  resistance  of  this  type. 

There  is  another  factor,  however,  which  may  importance 
throw  light  on  the  type  of  natural  immunity  just  Attacked?*'*^ 
considered.  We  know  that  tetanus  toxin  causes 
tetanus  through  its  power  of  uniting  with  the 
nerve  cells,  and  we  may  consider  that  tetanus  is 
a  very  fatal  disease,  primarily  because  of  the  vital 
nature  of  the  tissue  which  it  attacks.  Now,  if  the 
toxin,  instead  of  uniting  with  the  cells  of  a  vital 
organ,  were  to  combine  Avith  cells  of  less  impor- 
tance to  the  economy,  as,  for  example,  the  cells 
of  the  subcutaneous  tissue,  it  is  probable  that  we 
should  have  no  tetanus.  In  some  of  the  lower  ani- 
mals there  is  reason  to  believe  that  the  toxin  of 
tetanus  does  unite  with  such  tissue  (Metchnikoff). 
Roux  and  Borrel  believe  that  the  greater  degree  of 
immunity  to  tetanus  which  the  rabbit  has  over  the 
guinea-pig  is  due  largely  to  the  fact  that  the  rab- 


158  INFECTION    AND    IMMUNITY. 

bit's  liver  is  able  to  fix  a  great  deal  of  the  toxin. 
And  Metchnikoff  has  fonnd  that  the  liver  of  the 
scorpion,  which  has  an  absolute  immunity  to  tet- 
anus, absorbs  the  toxin  and  retains  it  for  months. 
Summary.  ^Yg  ma}^,  then,  enumerate  the  following  as  the 
factors  which  probably  are  responsible  for  the  dif- 
ferent grades  of  natural  immunity  and  suscepti- 
bility to  various  bacteria  and  their  toxins:  the 
bactericidal  and  antitoxic  powers  of  the  serum  and 
plasma;  the  destructive  effects  of  the  phagoc3^tes 
and  other  cells  on  both  bacteria  and  toxins;  a  pos- 
sible absolute  non-susceptibility  in  some  cases  (the 
absolute  non-existence  of  suitable  cell  receptors) ; 
the  lack  of  suitable  available  food  for  the  micro- 
organisms in  some  instances  (atreptic  immunity; 
see  the  preceding  chapter)  ;  the  overwhelming  dis- 
tribution of  the  '^suitable"  cell  receptors  in  organs 
of  less  vital  necessity  for  the  individual,  thus 
diverting  the  poisons  from  the  more  important 
organs. 

This  knowledge  is  Yery  general,  however,  and  in 
many  specific  instances  we  continue  to  be  in  doubt 
regarding  the  exact  conditions  which  are  respon- 
sible for  natural  immunity  and  susceptibility.  We 
have  no  reason  to  believe  that  any  one  factor  is 
operative  for  all  infections,  although  phagocytosis 
appears  to  be  more  general  in  its  action  than  the 
other  processes  mentioned.  Each  disease  must  be 
studied  as  a  unit  in  relation  to  each  species  of 
animal.  In  one  instance  the  resistance  or  suscepti- 
bility may  depend  on  the  bactericidal  power  of  the 
body  fluids;  in  another,  on  the  germicidal  action 
of  the  leucocytes  and  other  cells;  in  another,  on  the 
antitoxic  (destructive)  action  of  the  cells  or  fer- 
ments with  or  without  the  presence  of  true  "anti- 


HEMOLYSIS.  159 

toxins"  in  the  serum,  etc.  There  is  reason  to 
believe  that  two  or  more  different  protective  proc- 
esses may  come  into  operation  at  the  same  time 
against  a  given  infection. 

Eegarding  natural  antitoxic  immunity,  it  seems 
probable  that  we  have  no  example  in  which 
the  resistance  can  be  satisfactorily  explained  solely 
by  the  quantity  of  "antitoxins"  which  are  dem- 
onstrable in  the  serum ;  rather  we  must  assume  the 
existence  of  other  means  of  destroying  and  resist- 
ing toxins,  as  mentioned  above. 

In  order  that  a  pathogenic  organism  may  pro- 
duce a  progressively  fatal  disease  in  a  susceptible 
animal,  the  following  obstacles  must  be  sur- 
mounted: The  strong  defenses  of  the  body  sur- 
faces must  first  be  overcome ;  a  local  inflammatory 
reaction  which  may  have  been  excited  must  first 
prove  itself  to  be  inadequate  for  the  limitation  of 
the  infection;  there  must  be  an  insufficient  supply 
or  insufficient  activity  of  antimicrobic  and  anti- 
toxic processes  in  the  body  fluids  and  cells. 

Other  Properties  of  Normal  Serums 

In  addition. to  the  bactericidal  and  antitoxic  ac-  Hemolysis. 
tion  of  many  normal  serums,,  they  often  possess 
other  characteristics  which  are  of  the  highest  in- 
terest in  the  study  of  immunity.  In  earlier  days 
it  had  been  noted  that  the  transfusion  of  blood 
from  one  species  to  another  was  often  fatal  to  the 
injected  animal.  Later  investigations  showed 
that  this  was  due  to  toxic  substances  in  the  trans- 
fused blood ;  substances  which  agglutinated  and  de- 
stroyed the  red  blood  cells  of  the  injected  animal. 
The  process,  in  which  the  hemoglobin  is  dissolved 
out  of  the  red  blood  cells,  may  be  reproduced  in 


160  IXFECTIOy    AND    IMMUNITY. 

test-tube  experiments  by  mixing  the  blood  cells  of 
one  animal  with  the  serum  of  another  which  is 
toxic  (e.  g.,  rabbit  blood  -j-  goat  serum).  This  is 
the  phenomenon  of  hemolysis,  and  the  appearance 
of  such  a  tube  is  exactly  like  that  seen  when  blood 
is  mixed  with  distilled  water  or  even  with  tap 
water;  i.  e.,  it  is  a  laking  of  the  blood,  it  loses  its 
opacity  and  assumes  a  beautiful  cherry-red  color. 
The  serum  of  practically  every  species  contains  a 
hemolytic  substance  (a  serum  hemolysin)  for 
some  kind  of  erythrocyte. 
Cytotoxiiis.  Some  serums  also  contain  toxic  agents  for  other 
cells;  they  are  generally  called  serum  cytotoxins. 
The  serum  of  the  eel  not  only  contains  a  strou.i: 
hemoh'sin,  or  hemotoxin,  but  also  a  powerful 
poison,  for  nervous  tissue,  neurotoxin.  Similarly 
we  have  normal  leucotoxins  for  leucocytes,  nephro- 
toxins  for  kidney  tissue,  etc. 

Assintinins.  Another  property  of  many  normal  serums  is 
that  which  causes  agglutination  or  clumping  of 
bacteria,  as  one  sees  it  in  the  Gruber-Widal  test 
for  typhoid.  Even  normal  human  serum  may  ag- 
glutinate the  typhoid  bacillus,  but  to  a  less  degree 
than  that  of  a  typhoid  patient. 
Precipitins.  One  scrum  often  causes  a  precipitate  in  the 
serum  of  another  animal,  or  in  a  bacterial  culture 
filtrate. 

In  many  instances,  a  foreign  serum  which  is 
not  particularly  toxic  on  first  injection,  becomes 
very  poisonous  when  administered  (subcutane- 
ously)  a  second  time.     (See  "Anaphjdaxis.") 

In  considering  these  facts,  one  becomes  con- 
scious of  the  great  complexity  of  that  substance 
which  plays  so  important  a  part  in  immunity  and 
its  studv — i.  e.,  the  blood  serum. 


CHAPTER  X. 


ACQUIRED    IMMUNITY. 

Acquired  immunity  may  be  either  active  or  pas- 
sive: active  when  it  arises  as  a  consequence  of 
infection  or  artificial  immunization  (vaccination)  ; 
passive^  when  protective  or  curative  serums  are 
injected. 

One  who  has  recovered  from  scarlet  fever,  small-  :A.ctive 
pox,  plague^  typhoid  fever,  etc.,  becomes  possessed 
of  lasting  protection  against  subsequent  attacks.  On 
the  other  hand,  the  immunity  afforded  by  an  at- 
tack of  certain  other  diseases  usually  is  of  shorter 
duration:  cholera,  diphtheria,  pneumonia,  etc.  So 
far  as  known^  the  acquired  protection  is  specific 
in  character :  that  is,  a  person  who  has  had  measles 
may  still  have  scarlet  fever ;  or  an  attack  of  cholera 
does  not  protect  against  a  later  attack  of  typhoid. 

In  a  number  of  diseases  one  attack  confers  no 
evident  protection  against  a  second:  gonorrhea, 
influenza,  recurrent  fever  and  malaria.  Some  dis- 
eases may  create  a  predisposition  for  recurrence: 
erysipelas,  influenza,  diphtheria  in  some  instances, 
although  a  natural  susceptibility  of  the  individual 
may  explain  repeated  attacks.  The  mere  fact  of 
recovery,  however,  is  sufficient  evidence  of  at  least 
a  temporary  immunity.  It  is  evident,  therefore, 
that  among  the  various  infectious  diseases  different 
grades  of  active  immunity  must  be  recognized. 

Certain  chronic  diseases  are  of  particular  inter- 
est in  this  connection,  as  pointed  out  in  Chapter 


162  INFECTION     AND     IMMUNITY. 

VII.  On  first  thought  it  would  seem  tliat  immun- 
chronic  ity  can  havc  no  place  in  an  infection  of  lonff  dura- 
tion,  from  which  recover}^  is  rare  or  does  not  occur. 
This,  however,  is  not  necessarily  true,  and  the  very 
chronicity  of  the  infection  may  in  some  instances 
depend  on  the  establishment  of  a  certain  degree  of 
acquired  immunity.  It  is,  of  course,  possible  that 
in  other  instances  chronicity  depends  on  a  low 
degree  of  virulence  on  the  part  of  the  micro- 
organisms or  a  low  natural  susceptibility  on  the 
part  of  the  host.  Sleeping  sickness  may  be  taken 
as  an  example  of  a  chronic  disease,  the  prolonged 
course  of  which,  in  all  probability,  depends  on  the 
formation  of  protective  substances.  This  is  indi- 
cated from  the  fact  that  an  acute  is  followed  by  a 
chronic  stage.  At  the  height  of  the  acute  stage 
trypanosomes  are  very  numerous  in  the  blood,  but 
after  a  time  their  number  decreases  and  eventually 
it  is  difficult  to  find  them  except  in  organs  which 
serve  as  reservoirs  for  them.  Ehrlich  speaks  of 
this  type  of  immunity  as  Immunitas  non  sterili- 
sans.  It  may  disappear  more  or  less  completely, 
its  disappearance  being  marked  by  a  recurrence  of 
acute  trypanosomiasis. 

The  existence  of  this  temporary  immunity  to 
trypanosomiasis  was  demonstrated  in  mice  by 
Franke.  When  mice,  infected  with  mal  de  caderas 
(a  variety  of  trypanosomiasis)  are  given  an  injec- 
tion of  a  sufficient  quantity  of  "trypanrot,"  all  the 
trypanosomes  are  killed  and  the  cure  is  immediate. 
If  a  smaller  quantity  of  "trypanrot"  is  injected,  it 
may  still  be  sufficient  to  free  the  circulation  from 
parasites  for  twenty  or  thirty  days,  after  which 
general  invasion  again  occurs.  During  this  period 
of  comparative  freedom  from  parasites  the  animals 


PERIODIC     IMMUNITY.  163 

are  relatively  immune,  which  is  shown  by  inability 
to  reinfect  them  with  trypanosomes  of  the  same 
species.  After  this  period  is  passed  they  succumb 
very  quickly.  That  the  heightened  resistance  is 
not  due  to  the  presence  of  a  residuum  of  "trypan- 
rot'^  in  the  body  is  shown  by  the  fact  that  suscepti- 
bility for  other  species  of  trypanosomes  (as 
nagana)  is  retained.  In  other  words,  this  tem- 
porary immunity  is  somewhat,  if  not  absolutely, 
specific.  It  probably  is  brought  about  by  rapid 
active  immunization  consequent  on  the  disintegra- 
tion of  many  parasites  following  the  administra- 
tion of  the  "trypanrot." 

The  conditions  in  syphilis  and  piroplasmosis 
would  seem  to  be  similar  to  that  in  sleeping  sick- 
ness; i.  e.,  during  and  following  general  invasion, 
reinfection  from  without  does  not  occur,  although 
the  disease  is  still  active  in  some  part  of  the  body. 
In  both  syphilis  and  trypanosomiasis  reinvasion 
from  within  may  occur,  presumably  following  the 
disappearance  of  the  temporary  immunity. 

In  still  another  infection,  relapsing  fever,  it 
would  seem  to  be  similar  to  that  in  sleeping  sick- 
and  reinvasion  alternate  before  the  course  is  com- 
pleted. It  is  not  clear  why  the  micro-organisms 
are  not  entirely  killed  off  during  the  periods  of 
temporary  immunity.  Several  factors  may  be 
involved.  During  the  periods  of  remission  the 
spirilla  leave  the  general  circulation  and  are  found 
in  some  of  the  solid  organs,  particularly  the  spleen. 
At  this  time  they  may  be  protected  to  some  degree 
by  an  existence  in  organs  which  are  relatively  free 
from  germicidal  agents.  During  this  period  also 
the  less  resistant  organisms  may  be  destroyed  and 
those  which  remain  may  undergo  an  adaptation  to 


Periodic 
Immunity. 


164  INFECTION     AND     IMMUNITY. 

the  protective  agencies  of  the  host,  which  would  be 
equivalent  to  an  immunization  against  the  anti- 
bodies of  the  host.  The  recurrence  of  general 
invasion  may  also  coincide  with  a  disappearance  of 
the  general  blood  immunity. 
ProiojEoau  Concerning  such  chronic  infections  Ehrlich  may 
tions.  be  quoted  ("Chemotherapeutische  Trypanosomen- 
Studien/'  Berl.  Tclin.  Wclmsclir.,  1907^,  No.  9-12)  : 
"In  accordance  with  the  views  which  Eobert  Koch 
has  developed  regarding  malaria,  I  assume  that  in 
various  protozoan  diseases  an  immunity  of  perma- 
nent character  is  far  from  occurring  as  readily  as 
in  the  majority  of  the  bacterial  diseases,  and  that 
a  certain  degree  of  permanent  immunity,  charac- 
terized by  the  presence  of  antibodies,  is  obtained 
only  after  prolonged  invasion  of  the  body,  demand- 
ing particularly  a  large  number  of  recurrences. 
If  the  immunity  attained  is  not  sufficient  to 
destroy  all  the  parasites,  those  Avhich  remain 
accommodate  themselves  to'  the  injurious  agents 
which  are  present.^' 

It  has,  indeed,  been  suggested  that  a  general 
principle  prevails  to  the  effect  that  any  infection 
in  which  an  attack  confers  strong  and  lasting 
immunity  must  be  bacterial  rather  than  protozoan 
in  its  etiology.  This  does  not  imply,  of  course, 
that  all  bacterial  diseases  confer  strong  immunity; 
there  are  many  examples  to  the  contrary,  as  already 
.  stated,  although  a  sufficient  number  of  examples 
are  known  to  render*  it  of  suggestive  value  in  the 
study  of  diseases  of  unknown  etiology. 

A  very  important  factor  for  progress  in  artifi- 
cial immunity  was  the  knowjodge  that  even  a  light 
attack  of  an  infection  (scarlet  fever,  cholera, 
typhoid,  smallpox)  may  be  efficient  in  conferring 


VACCINATION.  IGo 

iInmlmit3^  Sucli  light  attacks  are  frequently 
noted  sporadically  and  in  epidemics,  while  occa- 
sionally an  epidemic  is  mild  in  character  through- 
out. Epidemics  of  benign  smallpox  occur  fre- 
quently. In  these  instances  it  seems  probable  that 
the  mild  character  of  the  disease  depends  on  the 
low  virulence  of  the  strain  which  causes  the  infec- 
tion; and  the  condition  suggests  the  possibility  of 
artificial  attenuation  of  virulent  micro-organisms 
for  the  purpose  of  inducing  at  will  infections  of  a 
benign  character. 

It  might  be  possible  so  to  modify  the  virus  that  vaccination. 
protection  could  be  established  without  setting  in 
motion  the  actual  disease  even  in  a  mild  form. 
An  attenuation  of  this  nature  had  long  been  prac- 
ticed with  smallpox  virus.  Before  cowpox  was 
resorted  to  as  a  source  of  vaccine,  it  had  been  the 
custom  to  inoculate  the  genuine  virus  of  smallpox, 
for  the  purpose  of  producing  immunity.  Con- 
trary to  the  natural  expectation,  this  method, 
instead  of  reproducing  severe  smallpox,  often 
caused  the  modified  disease  called  variola  inocu- 
lata.  This  phenomenon  may  depend  on  the  fact 
that  the  virus  finds  the  skin  and  subcutaneous 
tissue  an  unfavorable  medium  for  the  development 
of  virulence;  a  condition  which  would  be  equiva- 
lent to  an  attenuation  of  the  microbe.  The  patho- 
genicity of  the  cholera  vibrio  in  animal  experi- 
ments is  affected  similarly  in  subcutaneous  injec- 
tions. It  is  now  generally  considered  that  cowpox 
is  smallpox  which  has  suffered  a  decrease  in  viru- 
lence because  of  its  passage  through  the  cow. 
Consequently,  when  this  weakened  virus  is  planted 
in  the  skin  of  man,  where  it  may  undergo  further 
attenuation  and  produce  the  mildest  possible  form 


Attenuation. 


166  INFECTION     AND     IMMUNITY. 

of  modified  smallpox,  we  have  an  ideal  vaccine. 
In  a  similar  manner  the  virulence  of  the  anthrax 
bacillus  for  sheep  may  be  lessened  by  passing  the 
organism  through  the  dove.  This  method  of  de- 
creasing, or  in  some  cases  of  increasing,  the  viru- 
lence of  a  micro-organism  was  referred  to  in  Chap- 
ter VII  under  "passage." 

ISTo  single  method  of  attenuation  is  suitable 
for  all  organisms.  Pasteur  found  that  cultures 
of  the  bacillus  of  chicken-cholera  become  so  weak- 
ened when  exposed  to  the  action  of  light  and  air 
that  they  may  safely  be  used  as  vaccine;  also  that 
the  anthrax  bacillus  when  grown  at  42°  C.  is  at- 
tenuated and  does  not  form  spores,  and  conse- 
quently becomes  a  suitable  vaccine  for  sheep  and 
cattle.  Of  no  less  interest  to  us  is  Pasteur's 
method  of  attenuating  the  virus  of  hydrophobia 
by  desiccating  the  spinal  cords  of  infected  ani- 
mals (rabbits) ;  the  altered  virus  is  then  suitable 
for  the  immunization  of  individuals  who  have 
been  bitten  by  a  rabid  animal. 

Work  of  the  past  decade  has  shown  that  suc- 
cessful vaccination  is  possible  against  cholei-a, 
typhoid  and  plague  by  the  inoculation  of  avirii- 
lent  cultures,  or  those  which  have  been  killed  out- 
right by  heat.  In  so  far  as  we  know  the  immunity 
which  is  caused  by  vaccination  or  protective  in- 
oculation is  antibacterial,  or,  better,  antimicrobic. 
This  point,  however,  is  difficult  to  determine  in 
relation  to  diseases  of  unknown  etiology,  or  in  the 
event  that  the  micro-organism  does  not  lend  itself 
to  the  necessary  experimental  manipulations 
(smallpox,  hydrophobia).  It  is  possible  that  the 
protection  may  be  largely  antitoxic  in.  some 
instances.     In  Wright's  method  of  the  therapeutic 


Tlie  Serum 
in   Active 


H/JJUM     J.V    ACTIVE     IMMUNITY.  167 

t 

inoculation  of  killed  cultures  or  bacterial  products 
(e.  g.,  staphylococci,  tuberculin)  the  attempt  is 
definitely  made  to  increase  the  opsonins  and  other 
antibodies  in  the  patient's  blood. 

One  may  ask  if  acquired  immunity  to  bacteria 
and  to  toxins  is  due  to  the  presence  of  the  anti-  immunity. 
bacterial  and  antitoxic  substances  which  were 
mentioned  in  connection  with  natural  immunity. 
Although  normal  serum  is  strongly  bactericidal 
for  the  typhoid  bacillus,  the  serum  of  one  who  has 
recovered  from  typhoid  fever  possesses  this  power 
to  a  much  greater  degree.  As  this  is  true  in  many 
other  bacterial  infections,  the  new  resistance  is 
held  to  depend  on  the  increase  of  bactericidal  sub- 
stances in  the  serum.  Similarly  in  acquired  im- 
munity to  diphtheria  and  to  tetanus,  the  most 
conspicuous  change  is  a  great  increase  in  the  cor- 
responding antitoxins.  The  result  is  the  same, 
regardless  of  whether  the  immunity  be  produced 
by  a  natural  attack  of  the  disease,  or  by  artificial 
immunization  with  the  specific  microbe  or  toxin. 
Accordingly  it  seems  probable  that  acquired  im- 
munity in  these  instances  depends  on  the  presence 
in  the  serum  of  an  increased  amount  of  properties 
which,  to  a  certain  degree,  may  be  present  nor- 
mally. On  the  other  hand,  acquired  immunity  is 
not  always  represented  by  an  increase  in  the  bac- 
tericidal or  antitoxic  power  of  the  serum.  Bac- 
tericidal antibodies  may,  indeed,  be  formed,  but,  if 
so,  the  micro-organisms  concerned  are  not  sus- 
ceptible to  their  action.^    This  is  the  case  with  the 

1.  By  the  method  of  complement  fixation,  which  will  be 
explained  later,  it  has  indeed  been  shown  that  practically  all 
organisms  are  able  to  cause  the  formation  of  some  type  of 
antibody. 


168 


INFECTION     AND     IMMUNITY. 


The  IjCTicocytes 
In  Active 
Immimity. 


Opsonins. 


streptococcus,  staphylococcup,  pneumococcus,  and 
several  others. 

It  was  stated  in  the  section  on  natural  immun- 
ity that  the  leucocytes,  acting  as  phagocytes  and 
as  resorptive  cells,  seem  to  be  responsible,  at  least 
in  part,  for  natural  resistance  to  an  infection,  and 
there  is  now  no  lack  of  evidence  to  show  that  they 
are  of  great  importance  for  acquired  immunity,  at 
least  in  many  instances.  Particularly,  Metchni- 
koff  and  his  followers  have  provided  us  with  many 
observations  which  go  to  prove  this  point. 

These  investigators  showed  that  in  acquired 
immunity  the  phagocytes  have  a  much  greater 
capacity  for  ingesting  and  killing  bacteria  and  for 
absorbing  and  destroying  toxins  than  when  the 
animal  is  in  a  state  of  greater  susceptibility.  It  is 
also  concluded  that  the  serum  in  active  immunity 
owes  its  new  or  more  powerful  antibacterial,  anti- 
toxic and  other  properties  to  the  leucocytes,  which 
under  the  influence  of  the  infection  have  produced 
these  substances  in  excess  and  excreted  them  into 
the  plasma. 

The  views  of  Metchnikoff  regarding  the  impor- 
tance of  phagocytosis  have  been  greatly  strength- 
ened in  recent  years  as  a  consequence  of  quantita- 
tive studies  of  phagocytosis  in  vitr-o.  As  already 
stated,  phagocytosis  of  bacteria  depends  on  their 
first  being  "sensitized''  by  the  opsonins  which  are 
present  in  the  serum.  In  1895,  Denys  and  Le 
Clef  demonstrated  that  the  serum  of  animals 
which  liad  been  immunized  with  streptococci 
induced  a  much  greater  phagocytosis  and  destruc- 
tion of  these  organisms  than  normal  serum,  deter- 
mining their  results  by  means  of  plate  cultures 
and  microscopic  studies.    More  recently,  by  means 


PASSIVE    IMMUNITY 


169 


of  the  technic  evolved  b}'  Leishman  and  by 
Wright,  this  principle  has  been  found  to  have  a 
wide,  almost  universal  application :  in  other  words, 
active  immunization,  as  in  a  natural  infection  or 
by  the  injection  of  bacterial  cells,  is  almost  invari- 
ably accompanied  by  an  increase  in  opsonins,  which 
appears  to  coincide  with  an  increase  in  the  phago- 
cytic power  of  the  blood. 

Inasmuch  as  it  has  proved  possible  by  the  pro- 
longed immunization  of  animals  with  bacteria  or 
toxins  to  induce  a  high  concentration  of  antibac- 
terial or  antitoxic  substances  in  their  serum,  it 
was  the  natural  expectation  that  if  such  serums 
were  injected  into  other  animals  the  latter  would 
thereby  be  endowed  with  an  increased  resistance 
to  the  infectious  agent  against  which  the  serum 
had  special  activities  (passive  immunization). 
This  has  been  found  to  be  the  case  with  many 
antibacterial  (typhoid,  cholera,  plague,  dysentery, 
etc.)  and  some  antitoxic  serums  (diphtheria,  teta- 
nus). Unfortunately  the  protection  afforded  by 
the  injection  of  an  immune  serum  is  of  short  dura- 
tion (from  two  to  several  weeks) ;  it  is  as  if  a  for- 
eign substance  had  been  injected,  the  fate  of  which 
is  to  be  eliminated  rapidly.  This  is  in  contrast 
to  the  condition  in  active  immunity,  in  which  the 
protective  substances  are  often  formed  over  a  long 
period  by  the  body  cells. 

The  school  of  Metchnikoff  brings  the  leucocytes 
into  relation  with  passive  as  well  as  active  im- 
munity. It  is  held  that  the  immune  serum  which 
is  injected  is  potent,  because  it  stimulates  the  leu- 
cocytes to  a  greater  phagocytic  activity  in  the  case 
of  antibacterial  immunity,  or  to  a  greater  absorp- 


Passlve 
Inimiinlty. 


Tlie    Leucocytes 
in    Passive 
Immunity. 


and    Opsonins. 


170  INFECTION     AND     IMMUNITY. 

tion  and  destruction  of  toxins  in  the  ease  of  anti- 
toxic immunity. 
"stimniins"  It  is  uow  knowu,  as  stated,  that  an  immune 
serum  favors  j^hagocytosis  because  of  its  action  on 
the  bacteria  rather  than  on  the  leucocytes;  hence 
the  position  of  Metchnikoff^s  "stimulins/"'  which 
were  supposed  to  stimulate  the  leucocytes  to  an 
increased  phagocytosis,  does  not  seem  to  be  on  a 
good  footing  at  present.  The  value  of  the  opsonins 
in  passive  immunity  is,  indeed,  an  unknown  fac- 
tor; the  question  is  hardly  determined  finally. 
Some  of  the  opsonins  deteriorate  very  quickly; 
hence  they  could  be  of  no  value  in  serums  as  they 
are  placed  on  the  market.  Others  are  more  resist- 
ant, and  may  have  a  certain  value  in  passive  immu- 
nization, although  they  probably  do  not  approxi- 
mate in  importance  the  bactericidal  and  antitoxic 
substances. 

By  way  of  summary  we  may  say  that  bacterici- 
dal substances,  antitoxins  and  opsonins  are  the 
known  and  demonstrable  factors  in  active  immun- 
ity. It  does  not  follow  that  all  three  factors  come 
into  play  in  every  conceivable  infection;  or  that  if 
they  do,  in  some  particular  disease,  the  three  are 
equally  important.  Thus,  in  typhoid  fever,  the 
serum  has  an  enhanced  bactericidal  power,  and 
investigations  seem  to  show  that  the  opsonins  are 
also  increased ;  on  the  other  hand,  we  have  no 
evidence  to  show  that  acquired  immunity  to 
typhoid  fever  is  antitoxic.  In  diphtheria  and  teta- 
nus, the  immunity  is  represented  by  the  presence 
of  antitoxins  in  the  serum,  whereas  the  opsonins 
and  bacteriolysins  appear  to  be  of  less  importance. 

Another  condition  is  found  in  infections  with 
staphylococci,  streptococci,  pneumococci  and  some 


Summary, 


HABITUATION     TO     TOXINS.  171 

other  organisms,  in  which  the  only  demonstrahle 
change  of  importance  is  an  increase  in  the  opso- 
nins, and  with  this  an  increase  in  the  power  of 
phagocytic  destruction  of  the  cocci. 

In  some  chronic  infections  it  is  possible  that  the 
individual  shows  a  resistance  to  the  bacterial 
toxins,  which  is  on  the  order  of  habituation,  or 
adaptation,  and  which  is  not  represented  by 
any  demonstrable  antitoxins.  Thus,  by  the  use 
of  gradually  increasing  doses  of  tuberculin,  an 
individual  may  eventually  tolerate  large  doses 
which  in  the  beginning  would  have  been  very 
toxic. 

In  spite  of  this  acquired  resistance,  however, 
the  body  appears  to  form  no  true  antitoxin  for  the 
tuberculin.-  After  the  cessation  of  treatment  the 
resistance  of  the  individual  gradually  returns  to 
normal;  that  is  to  say,  the  cells  return  to  their 
original  susceptibility. 

The  possible  relation  of  anaphylaxis  to  acquired 
immunity  will  be  discussed  in  the  chapter  on 
'^Anaphylaxis." 

Mention  may  be  made  here  of  the  well-known 
but  curious  phenomenon  that  resistance  may  vary 
with  the  age  of  the  individual.  Typhoid  fever  at- 
tacks the  adolescent  or  middle-aged  rather  than 
the  very  young  or  very  old.  Active  tuberculosis 
grows  less  common  in  the  later  decades  of  life. 
Then  we  have  what  are  distinctively  the  diseases 
of  childhood :  after  15  years  of  age  diphtheria,  for 
example,  is  uncommon.     Some  of  these  instances 

2.  Such  a  course  of  treatment  does  cause  the  formation 
of  antibodies  of  a  specific  character,  hut  they  appear  not  to 
be  antitoxic  in  character.  The  "antituberculin"  which  Was- 
sermann  recognizes  by  means  of  the  method  of  fixation  of 
complement  has  not  been  shown  to  be  an  antitoxin. 


Habituation. 


172  INFECTION     AND     IMMUNITY. 

of  acquired  immunity  may  be  referable  to  differ- 
ences in  the  character  of  the  cell  receptors  at  dif- 
ferent ages,  while  perhaps  others  are  due  to  a  slow 
immunizing  process  occasioned  by  the  prolonged 
presence  of  non-pathogenic  amounts  of  the  proper 
micro-organisms. 
Enzymes.  Emmcricli  and  Loew  found  that  many  bacteria 
produce  in  culture  media,  as  well  as  in  the  animal 
bod}^,  substances  which  apparently  act  as  ferments 
and  which  are  able  to  kill  not  only  the  bacterium 
which  secretes  the  ferment,  but  many  others.  For 
example,  pyocyanase,  the  bacteriolytic  enzyme  of 
Bacillus  pyocyaneus,  dissolves  pyocyaneus, 
anthrax,  diphtheria  and  typhoid  bacilli,  the  vibrio 
of  cholera,  the  streptococcus  and  staphylococcus. 
These  enzymes  usually  are  not  toxic,  and  it  has 
been  supposed  that  in  the  course  of  an  infection 
they  reach  such  a  concentration  in  the  blood  that 
they  destroy  the  bacteria  which  produced  them, 
thus  bringing  about  recovery.  It  is  asserted  also 
that  they,  either  during  infection  or  as  a  result  of 
repeated  injection  of  the  ferment,  enter  into  a 
somewhat  permanent  combination  with  the  al- 
bumin of  the  body,  forming  the  so-called  "im- 
mune-proteidins,"  on  which  acquired  immunity 
depends. 

It  is  also  stated  that  with  "pyocyanase-immune- 
proteidin"  it  is  possible  so  to  immunize  a  rabbit 
that  a  subsequent  (twelve  days)  otherwise  fatal 
dose  of  the  anthrax  bacillus  is  harmless. 

Although  the  effects  of  these  "enzymes"  on 
anthrax  and  on  some  other  organisms  have  been 
confirmed  by  a  number  of  investigators,  their  im- 
portance in  acquired  immunity  and  in  the  recov- 
ery from  infections  is  very  doubtful.    There  is  the 


NON-SPECIFIC     RESISTANCE.  173 

special  objection  to  this  theory  that  it  puts  im- 
munity on  a  non-specific  basis;  i.  e.,  pyocyanase 
will  protect  against  anthrax,  diphtheria,  etc., 
while,  in  reality,  all  our  clinical  and  experimental 
data  point  to  the  high  specificity  of  acquired 
immunity. 

In  contrast  to  the  specific  immunization  which 
may  be  accomplished  with  an  immune  serum,  it  is 
important  to  recognize  that  a  non-specific  increase 
in  resistance  may  be  caused  by  the  injection  of  a 
number  of  substances,  which  in  the  test-tube  have 
no  destructive  action  on  the  bacteria.  Issaeff 
injected  into  the  peritoneal  cavity  such  substances 
as  bouillon,  tuberculin  and  sterile  urine,  and  found 
\he  resistance  of  the  animals  increased  to  the  peri- 
toneal inoculation  of  virulent  organisms.  Normal 
serum  from  another  animal  has  a  similar  effect, 
but,  in  this  instance,  the  bactericidal  substances  of 
the  foreign  serum  may  be  a  factor  in  the  new 
resistance.  Supposedly,  this  non-specific  resistance 
is  local,  and  it  appears  to  depend  on  the  attraction 
of  an  increased  number  of  phagoc3^tesand  of  addi- 
tional complement  (alexin)  to  the  peritoneal  cav- 
ity. The  suggestion  that,  preceding  laparotomy^ 
nucleinic  acid  be  injected  into  the  abdominal  cav- 
ity, in  order  to  increase  the  local  resistance,  has 
its  foundation  in  the  experimental  work  cited. 

The  serum  of  an  animal  acquires  antibodies  not  immune 
only  for  bacteria  and  toxins,  but  also  for  many  <^y*o*o^«»»» 
other  cells  and  substances  which  may  be  injected. 
There  are  many  immune  cytotoxins,  such  as  the 
hemolysins,  leucotoxins,  neurotoxins,  nephrotoxins, 
etc.,  which  are  formed  as  the  result  of  immuniza- 
tion with  the  corresponding  cells.  (See  '^^Cyto- 
toxins.") 


174 


INFECTION     AND     IMMUNITY, 


Immune 
Assrlutiuins. 


mmnne    Precip- 
itins  and   tlie 
Biologric  Test 
for  Species. 


By  systematically  injecting  an  animal  with  a 
bacterium  or  with  any  tissue  cell^  agglutinating 
substances  (agglutinins)  are  formed  and  may  be 
demonstrated  in  the  serum.  Like  other  antibodies, 
they  are  highly  specific  for  the  cell  used  in  the 
immunization. 

It  has  been  found  that  toxins,  other  than  those 
of  bacterial  origin,  will  yield  antitoxins  by  im- 
munization. Such  toxins  are  snake  venom,  yield- 
ing antivenin;  ricin,  a  hemagglutinating  toxin 
from  the  castor-oil  bean,  yielding  antiricin,  etc. 

Recently  what  is  termed  the  biologic  test  for 
species  has  assumed  prominence.  This  test  may 
be  illustrated :  A  goat  is  injected  repeatedly  with 
the  serum  of  man.  After  a  number  of  injections 
a  very  minute  amount  of  this  goat's  serum  will 
cause  a  precipitate  when  mixed  with  human 
serum,  but  not  when  mixed  with  the  serum  of  any 
other  animal  (except,  perhaps,  that  of  anthropoid 
apes).  The  test  is  so  delicate  that  when  a  small 
amount  of  old  dried  human  blood  is  dissolved  in 
salt  solution  and  treated  with  the  goat  serum  the 
precipitation  will  still  occur,  and  in  view  of  this 
fact,  the  test  has  become  of  medicolegal  impor- 
tance. 

The  wide  distribution  of  this  phenomenon 
among  all  kinds  of  animals  gives  it  great  biologic 
significance,  particularly  as  regards  the  differentia- 
tion of  species. 

Kraus  found  that  by  immunization  with  cer- 
tain bacterial  filtrates  substances  are  formed  in 
the  serum  which  cause  precipitates  in  the  filtrates. 
It  is  further  interesting  that  other  albumin-con- 
taining substances,  as  egg  albumin  or  milk,  will 
on  immunization,  yield  specific  antibodies.     The 


ANTIFERMENTS.  175 

serum  of  an  animal  which  has  been  immunized 
with  goat's  milk  will  cause  a  precipitate  in  the 
latter,  but  not  in  cow's  milk.     (See  "Precipitins.") 

It  has  also  been  possible  to  obtain  specific  anti-  Antifennents. 

bodies  for  ferments :  for  the  peptonizing  ferments 
of  bacteria,  for  emulsin,  lab,  fibrin  ferments,  etc. 
There  are,  however,  a  great  many  substances  for 
which  antibodies  can  not  be  obtained;  this  is  true 
for  substances  of  known  chemical  composition, 
such  as  acids,  bases,  salts,  and  for  the  alkaloids 
(str3Thnin,  morphin,  aconite,  etc.) 


CHAPTEE    XI 


TOXINS  AND  ANTITOXINS. 

E^hriicii's       Through  Ehrlich  the  word  toxin  has  come  to 
of  Toxin,  have  a  special  significance,  being  applied  only  to  a 
certain  type  of  toxic  substances.    According  to  his 
original  conception  they  have  the  following  prop- 
erties : 

1.  They  are  extremely  labile  substances  which 
occur  as  secretion  products  of  vegetable  or  of  ani- 
mal organisms. 

2.  Their  chemical  nature  is  unknown.  The  im- 
possibility of  obtaining  them  in  pure  form  and 
their  great  lability  render  them  insusceptible  to 
ordinary  chemical  analysis. 

3.  An.  analysis  of  a  toxin  may  be  reached  at 
present  only  through  the  medium  of  biologic  ex- 
periments. 

4.  Immunization  with  toxins  yields  antitoxins. 
It  has  not  been  possible  to  obtain  antitoxins  for 
inorganic  poisons,  glucosids  and  alkaloids 
(morphin,  strychnin,  etc.) 

5.  In  contrast  to  well-defined  chemical  poisons, 
the  action  of  toxins  is  characterized  by  a  latent  or 
incubation  period.  That  is,  following  the  introduc- 
tion of  a  toxin,  a  certain  period  of  time  elapses 
before  toxic  symptoms  appear,  and  this  period  is 
greater  than  the  time  logically  required  for  the 
absorption  of  the  toxin  through  the  circulation.^ 

1.  Recent  work  Indicates  that  the  long  incubation  period 
of  tetanus  may  depend,  at  least  in  part,  on  the  length 
of  time  required  for  the  toxin  to  reach  the  ganglion  cells 
through   the  axis   cylinders   of  the   motor   nerves. 


TOXINS.  177 

The  incabation  period  may  be  shortened  experi- 
mentally by  the  injection  of  large  quantities  of 
toxin,  but  it  can  not  be  eliminated  entirely.  The 
poisons  of  snake  venoms  appear  to  act  without  in- 
cubation period,  but  they  are  still  to  be  classed 
with  the  toxins,  because  of  their  power  to  cause 
the  formation  of  antitoxins. 

6.  "The  facts  make  it  necessary  to  assume,  as  a 
condition  for  the  poisonous  action  of  toxins,  a  spe- 
cific chemical  union  of  the  toxin  with  the  proto- 
plasm of  the  cells  in  certain  organs."  .  .  .  "The 
affinity  of  other  poisons,  as  the  alkaloids,  for 
tissues,  depends  not  on  chemical  union,  but  on 
some  such  process  as  solid  solution  or  loose  salt 
formation/' 

The  -preparation  of  the  soluble  toxins  of  bacteria  Preparation 

.  of  Toxins. 

is  relatively  simple.  It  is  necessary  only  to  inocu- 
late a  suitable  fluid  medium  with  a  culture  of  the 
microorganism,  to  allow  growth  to  take  place  for 
some  days  at  body  temperature,  then  to  pass  the 
fluid  through  a  porcelain  or  some  equivalent  filter. 
The  soluble  toxins  usually  may  be  precipitated 
from  the  filtrate  by  some  precipitant,  as  ammon- 
ium sulphate,  and  preserved  in  a  dried  state  for  a 
long  period.  Such  a  precipitate  does  not  represent 
the  toxin  in  a  pure  form,  but  various  proteid  sub- 
stances of  the  culture  medium,  as  well. 

The  bacilli  of  diphtheria  and  tetanus,  Bacillus 
pyocyaneus,  and  Bacillus  hotulinus,  are  the  princi- 
pal micro-organisms  whicli  produce  soluble  toxins. 

When  the  toxins  of  these  organisms  are  injected 
into  a  suitable  animal,  phenomena  similar  to  those 
produced  by  an  infection  with  the  organisms 
themselves  are  produced.     They  are  in  a  particu- 


178  INFECTION     AND     IMMUNITY. 

lar  sense  specific  toxins.  Some  micro-organisms, 
however,  produce  more  than  one  toxin.  The  teta- 
nus bacillus,  for  example,  secretes,  in  addition  to 
the  toxin  causing  the  nervous  symptoms  of  tetanus, 
another  (tetanolysin,  or  tetanus  hemolysin)  which 
has  the  power  to  destroy  red  blood  cells.  Ehrlich 
holds  that  the  diphtheria  bacillus  produces  not 
only  the  toxin  which  causes  the  acute  intoxication 
of  diphtheria,  but  another  of  long  incubation 
period  which  may  cause  paralysis.  Cobra  poison 
has  at  least  two  toxins,  one  which  attacks  the  nerv- 
ous tissues — a  neurotoxin — and  another  which  at- 
tacks the  erythrocytes;  the  two  may  be  separated 
by  appropriate  measures.  As  previously  stated, 
the  serum  of  the  eel  has  a  strong  neurotoxin  and 
a  hematoxin. 
Secondary  Somc  micro-organisms  produce  one  or  more 
soluble  toxic  substances,  which  it  is  often  difficult 
or  impossible  to  consider  as  the  actual  disease- 
producing  elements  of  these  organisms.  Concern- 
ing a  disease  which  is  so  well  characterized  clini- 
cally as  tetanus,  it  is  not  difficult  to  determine 
by  inoculation  experim.ent  whether  one  has  in  hand 
the  specific  toxin.  The  proof  is  naturally  much 
more  difficult  in  infections  with  streptococci  and 
staphylococci,  for  example,  in  which  the  group  of 
symptom. s  and  the  patholo,gic  conditions  are  not 
entirely  unique  for  the  infection.  We  are  by  no 
means  certain  that  the  hemolysin  or  the  leucoci- 
din  (toxin  for  leucocytes)  of  the  staphylococcus, 
or  the  hemolysin  of  the  streptococcus  are  the  para- 
mount disease-producing  toxins  of  these  organisms, 
although  these  substances  are  true  toxins. 


TOXINS.  179 

An  important  test  for  the  pathogenic  signifi- 
cance of  a  toxin  lies  in  its  ability  or  inability  to 
cause  the  formation  of  an  antitoxin  which  is 
efficient  in  the  treatment  of  an  infection  by  the 
corresponding  organism.  This  is  not  the  case 
with  the  toxins  jast  mentioned.  However,  one 
should  not  place  too  much  importance  on  such  a 
test,  for  it  is  possible  that  we  are  not  able  on 
artificial  culture  media  to  obtain  the  toxin  in 
such  concentration  that  the  production  of  an  effi- 
cient antitoxin  is  possible. 

There  is  a  large  class  of  organisms  the  members  intracellular 
of  which  apparently  do  not  produce  soluble  toxins ;  Endotoxins. 
such  organisms,  however,  cause  highly  toxic  diseases 
(e.  g.,  typhoid,  cholera,  plague).  The  dead  or 
ground-up  bodies  of  such  bacteria  are  very  toxic; 
al?o  when  the  germs  disintegrate  by  a  process  of 
autolysis  or  self-digestion  the  culture  medium  be- 
comes toxic  because  of  the  cell  contents  which  are 
set  free.  Such  organisms  are  said  to  contain  in- 
tracellular toxins  or  endotoxins.  In  infections  by 
them  it  is  supposed  that  toxic  symptoms  are  pro- 
duced when  a  pathogenic  amount  of  the  intracel- 
lular toxins  is  liberated  by  the  bacteriolytic  action 
of  the  body  fluids  or  cells  (phagocytes). 

Xothing  is  known  of  the  nature  of  such  toxins. 
They  certainly  are  very  different  from  the  soluble 
toxins  of  diphtheria  and  tetanus,  since  immuniza- 
tion with  them  has  not  as  yet  resulted  in  tlie  pro- 
duction of  efficient  antitoxins.  In  spite  of  this 
fact,  however,  it  is  none  the  less  probable  that 
they  are  the  disease-producing  constituents  of  the 
organisms.  Buchner  gave  the  name  of  ^^plasmin" 
to  the  cell  juice  which  he  was  able  to  express  from 
some  micro-orsfanisms. 


180 


INFECTION     AND     IMMUNITY. 


The  Mac- 
Fadyen 
Method. 


Accidental 

Toxic 

Substances. 


Preparation 
of    Antitoxins. 


MacFadyen,  by  grinding  large  masses  of  typhoid 
bacilli  and  other  organisms  which  had  been  rend- 
ered brittle  by  the  temperature  of  liquid  air, 
obtains  from  these  organisms  a  toxic  cell  juice. 
The  efficiency  of  the  antitoxins  which  he  is  said 
to  obtain  by  such  immunization  has  not  been 
demonstrated  practically.  It  seems  improbable 
that  immunization  with  such  "toxins"  will  yield  a 
serum  differing  in  properties  from  that  obtained 
by  immunization  with  the  living  organisms. 

Toxic  substances  obtained  from  bacteria  by  the 
action  of  strong  chemicals  and  extracting  fluids, 
may  not  represent  the  essential  toxic  substance  of 
the  organism,  but  perhaps  some  disintegration 
product  which  happens  to  be  toxic. 

It  is,  of  course,  common  knowledge  that  an  anti- 
toxin is  the  blood  serum  of  an  animal,  after  the 
latter  has  been  rendered  highly  immune  by  re- 
peated injections  of  the  corresponding  toxin.  The 
horse  is  chosen  for  immunization  because  of  its 
marked  ability  to  yield  antitoxins  (diphtheria, 
tetanus),  because  of  its  size,  withstanding  much 
loss  of  blood,  and  because  of  the  readiness  with 
which  it  submits  to  manipulation. 

Manufacturing  plants  which  produce  antitoxins 
and  other  antiserums  on  a  large  scale  have  splen- 
didly equipped  stables,  which  are  kept  in  the 
optimum  hygienic  condition,  and  from  which  rats 
in  particular  are  rigorously  excluded.^    The  horses 


2.  The  importance  of  this  is  very  great  If,  for  example, 
horses  are  receiviug  injections  of  some  virulent  living 
micro-organism  (as  the  plague  bacillus).  In  this  case 
living  micro-organisms  reach  the  general  circulation,  and  a 
rat  having  bitten  the  animal  could  well  contract  the 
plague  and  be  an  evident  source  of  danger,  not  only  to 
other  animals,  but  to  the  community  at  large.  Even  fly 
proof   stalls   are   properly    instituted    In   such   cases. 


TOXINS.  181 

are  carefully  groomed  and  nourished  and  given 
such  exercise  as  will  keep  them  in  a  healthy  con- 
dition. 

The  toxins,  in  solution,  are  injected  subcutane- 
ously.^  Grave  and  even  fatal  reactions  may  follow 
the  first  injections,  if  the  toxin  has  been  given  in 
too  large  doses  or  in  too  concentrated  solutions. 
This  is  especially  true  when  injecting  tetanus 
toxin.  It  is  of  great  importance  first  to  establish 
what  the  Germans  call  a  " Grundimmunitdt/' 
which  means  a  primary  immunity  in  the  animal 
itself  so  that  the  immunization  may  then  be 
pushed  vigorously  until  the  blood  contains  anti- 
toxin in  high  concentration.  For  this  purpose  it 
has  been  found  necessary  to  weaken  the  first  tox- 
ins injected.  This  may  be  done  by  heating  the 
toxin  solution  to  65  or  70  C.  for  an  hour ;  by  add- 
ing to  it  from  0.05  to  0.4  per  cent,  of  the  trichlo-  »*  Toxins. 
rid  of  iodin ;  or  by  adding  a  solution  of  potassium 
iodid  in  which  iodin  has  been  dissolved  (Lugol's 
solution)  or,  as  is  often  done  at  present,  by  par- 
tially neutralizing  the  toxin  with  antitoxin.  High 
dilutions  of  the  unaltered  toxin  may  also  be  used. 
Gradually  the  virulence  and  amount  of  the  toxin 
injected  may  be  increased  until  finally  the  full 
virulent  toxin  is  given  in  large  doses.  The  increase 
in  dosage  must  be  very  gradual.  Eventually  as 
much  as  a  liter  or  more  of  diphtheria  toxin  is 
tolerated. 

Following  each  injection  a  reaction  occurs. 
With  diphtheria  the  local  swelling  may  be  great, 
and  sloughing  may  occur.    Following  an  injection 

3.  For  the  production  of  antivenin  the  snake  venom  Is 
best  injected  intravenously. 


Attenaation 


182  INFECTION     AND     IMMUNITY. 

of  tetanus  toxin,  tetanic  symptoms  may  appear. 
In  either  case,  there  is  some  loss  of  weight  and 
often  fever,  and  another  injection  must  not  be 
given  until  the  original  weight  is  regaiued  and 
the  general  behavior  of  the  animal  indicates  that 
its  former  healthy  condition  is  re-established. 

Several  months  of  such  treatment  are  necessary 
for  the  production  of  diphtheria  antitoxin  in  high 
concentration.  At  the  end  of  this  time  blood  is 
drawn  from  the  jugular  vein  by  means  of  a  large 
trochar  to  which  a  rubber  tube  is  attached.  The 
tube  leads  to  a  tall  glass  cylinder  holding  from 
one  to  two  liters,  and  into  this  the  blood  is  allowed 
to  iiow.  Six  liters  may  be  drawn  safely  from  a 
horse  of  average  size.*  The  most  rigid  asepsis  is 
observed  in  taking  the  blood.  The  glass  cylinders, 
appropriately  covered  to  prevent  contamination, 
are  then  set  in  a  cool,  dark  place,  and  after  the 
serum  has  separated  from  the  clot  samples  are 
taken  to  be  tested  for  their  antitoxic  value. 
PreMervatiT-es  The  scrum,  in  bulk  or  after  being  bottled  for 
the  trade,  is  preserved  at  a  low  temperature  and 
in  the  dark,  0.5  per  cent,  of  carbolic  acid  having 
been  added  to  insure  sterility.  The  addition  of 
the  acid  may  cause  harmless  cloudiness  in  the 
serum,  but  does  not  destroy  the  antitoxin.  Serums 
may  be  preserved  perfectly  in  a  dried  or  frozen 
state. 

Many  facts  of  scientific  and  practical  impor- 
tance have  been  brought  to  light  through  the  im- 
munization of  animals  on  a  large  scale.     It  has 


of  Serums. 


4.  Some  horses  may  be  bled  as  many  as  forty  times 
without  suffering  a  conspicuous  deterioration  in  health.  In 
time,  however,  an  animal  becomes  less  valuable  as  an  an- 
titoxin producer. 


STANDARDIZATION     OF     SERUMS. 


183 


been  found,  for  example,  that  following  each  in- 
jection of  toxin  the  amount  of  antitoxin  in  the 
blood  suffers  a  reduction,  and  only  equals  or  rises 
above  the  previous  amount  eight  or  ten  days  later. 
This  decrease  is  explained  by  assuming  that  the 
toxin  has,  to  a  certain  extent,  united  chemically 
with  the  circulating  antitoxin.  It  indicates  also 
the  period  at  which  the  horse  should  be  bled  in 
order  that  the  greatest  amount  of  antitoxin  may 
be  obtained.  It  might  even  be  dangerous  to  draw 
the  blood  before  this  time  had  elapsed,  since  some 
free  toxin  might  still  be  in  the  circulation. 

It  is  noteworthy  that  all  horses  are  not  equally 
good  producers  of  antitoxin.  One  may  yield  a 
serum  of  three  times  the  value  of  another,  al- 
though the  two  have  been  treated  identically  and 
seem  to  be  equally  immune  to  the  toxin. 

Another  most  interesting  fact  is  that,  although 
the  blood  of  an  animal  may  be  very  rich  in  anti- 
toxin, he  still  may  have  a  disproportionate  sus- 
ceptibility to  fresh  injections  of  the  toxin. 

Many  of  these  phenomena  have  not  been  ex- 
plained satisfactorily. 

The  necessity  of  standardizing  antitoxins  so 
that  dosage  may  be  controlled  accurately  is  self- 
evident.  To  meet  this  need  the  antitoxic  unit 
familiar  in  practice  was  devised. 

Behring,  and  also  Ehrlich,  decided  arbitrarily 
to  consider  as  the  antitoxic  unit  that  quantity  of  a 
serum  which  would  protect  a  guinea-pig  from  100 
fatal  doses  of  the  toxin.  Ehrlich's  original  method 
of  testing  a  serum  was  to  mix  different  quantities 
with  10  fatal  doses  of  the  toxin  and  inject  each 
mixture  into  a  guinea-pig  of  from  250  to  300 
grams'  weight.    That  quantity  of  the  serum  which 


standardiza- 
tion of  Toxins 
and  Anti- 
toxins. 


184  INFECTION     AND     IMMUNITY. 

protected  the  animal  against  the  ten  fatal  doses  of 
toxin  contained  1/10  of  an  immunity  unit,  and 
from  this  result  the  number  of  units  in  a  cubic 
centimeter  could  be  calculated.  This  method  in- 
volved the  use  of  toxin  as  the  standard  by  which 
the  value  of  the  antitoxin  was  measured,  and  it 
was  found  to  be  unreliable.  A  toxin  degenerates 
rather  rapidly,  retaining  at  the  same  time  its 
binding  power  for  the  antitoxin;  hence  two  tests 
made  with  the  same  serum  two  months  apart 
might  indicate  different  antitoxic  values  for  the 
serum.  Also  10  fatal  doses  of  one  toxin  often  re- 
quired more  antitoxin  for  neutralization  than  the 
same  quantity  of  a  second  toxin.  These  phenomena 
are  due  to  the  formation  of  toxids.  (See  next 
chapter.) 
standard  On  account  of  thcsc  sources  of  error,  Ehrlich 
devised  a  new  method  in  which  a  standard  anti- 
toxin or  test-serum  is  used  as  the  starting  point 
for  the  valuation  of  a  new  serum.  The  test-serum 
used  at  the  Eoyal  Prussian  Institute  for  Experi- 
mental Therapy  at  Frankfurt,  of  which  Ehrlich 
•  is  the  director,  is  a  dried  and  powdered  serum  of 
such  strength  that  1  gram  contains  1,700  immun- 
ity units;  i.  e.,  1/1700  gm.  would  protect  a  guinea- 
pig  against  100  fatal  doses  of  a  diphtheria  toxin. ^ 

5.  In  Germany  the  various  serums  are  prepared  by  pri- 
vate individuals  or  corporations  and  manufacturers  are  re- 
quired to  send  a  sample  of  every  lot  of  serum  Intended  for 
the  trade  to  the  Frankfurt  Institute  that  its  exact  value  may 
be  determined.  Each  bottle  eventually  receives  a  stamp  sig- 
nifying the  value  in  antitoxin  units  of  the  contained  serum. 
Moreover,  samples  of  every  lot  of  serum  are  retained  in  the 
institute,  and  from  time  to  time  these  are  tested  ;  and  when 
it  is  found  that  the  samples  have  degenerated  beyond  a  cer- 
tain value  the  order  is  sent  out  to  call^  in  ail  serum  belong- 
ing  to   the   degenerated    lot.     When   a   manufacturer   thinlis 


STANDARDIZATION     OF     SERUMS.  185 

Any  other  high-grade  serum  would  have  answered 
equall}^  well. 

The  institute  keeps  in  stock  a  large  number  of 
vials,  each  containing  2  grains  of  this  dried 
serum.  The  air  and  moisture  are  exhausted  from 
each  vial  and  the  latter  is  then  sealed  in  the  flame. 
Once  in  three  months  one  of  these  vials  is  broken 
open  carefully  and  tlie  serum  dissolved  in  200  c.c. 
of  a  solution  made  up  of  equal  parts  of  glycerin 
and  10  per  cent,  salt  solution;  hence  each  cubic 
centimeter  of  the  solution  contains  17  units.  Dur- 
ing the  succeeding  three  months  this  antitoxic 
solution  is  used  in  the  comparative  valuation  of 
new  antitoxins;  the  solution  retains  its  strength 
unaltered  for  this'  period.  For  individual  tests 
the  serum-solution  just  described  is  again  diluted 
seventeenfold,  so  that  each  cubic  centimeter  con- 
tains one  unit.  This  adds  to  convenience  and  ac- 
curacy. 

The  first  step  in  the  process  is  to  standardize 
some  diphtheria  toxin  in  which  the  degenerative 
changes  (toxoid  formation)  have  come  to  a  stand- 
still. This  is  done  by  adding  so  much,  of  the  toxin 
to  1  unit  (1  c.c.)  of  the  test  serum  that  an  excess 
of  one  fatal  dose  of  the  toxin  remains  unbound  by 
the  antitoxin. 

The  quantity  of  the  toxin  which  gives  this  re- 
sult is  called  the  L+dose.®     The  LO  dose  of  the 

the  serum  of  one  of  his  horses  has  a  high  value  he  may 
draw  a  small  amount  of  blood  from  the  animal  and  send 
the  serum  to  Frankfurt  for  a  preliminary  test.  If  the 
serum  is  sufficiently  strong  he  may  then  bleed  the  horse 
freely ;  if  it  is  weak  he  will  be  advised  to  continue  the 
immunization  for  a  time. 

6.  D=Limes  (Limit)  :  -1-  is  commonly  used  to  indicate 
a  fatal  result. 


186  INFECTION     AND     IMMUNITY. 

toxin  also  is  determined,  this  being  the  amount 
which  is  exactly  neutralized  by  the  unit  of  anti- 
toxin. The  use  of  the  two  doses  serves  to  eliminate 
subjective  errors  On  the  part  of  the  observer.  The 
L-l-  and  LO  doses  of  toxin  are  then  used  to  de- 
termine the  value  of  new  antitoxins.  That  quan- 
tity of  the  new  serum  which,  when  mixed  with  the 
L+  dose  of  to.xin,  cause?  the  animal  to  die  in 
four  to  six  days,  contains  1  unit  of  antitoxin.  If, 
for  example,  1/100  c.c.  accomplishes  this  result, 
the  serum  is  of  one  hundredfold  strength,  i.  e.,  1 
c.c.  would  contain  100  antitoxic  units. 

In  accordance  with  the  Act  approved  July  1, 
1902,  the  United  States  Public  Health  and  Marine- 
Hospital  Service  has  established  a  standard  unit 
for  this  country.  The  unit  is  based  on  that  of 
Ehrlich  just  described  and  was  made  by  com- 
parison with  the  normal  unit  obtained  from  Ehr- 
lich's  Institute,  Frankfort  a.  M.,  Germany. 

Antitoxins  are  purchased  on  the  open  markets 
by  officers  of  the  Public  Health  and  Marine- 
Hospital  Service  and  tested  in  the  Hygienic 
Laboratory  for  potency,  freedom  from  contamina- 
tion by  bacteria  and  chemical  poisons,  especially 
tetanus  toxin,  and  finally  to  insure  against  excess 
of  preservatives. 

The  method  of  determination  of  potency  is  sim- 
ilar to  that  used  by  Ehrlich  and  previously 
described. 

White  mice  are  inoculated  to  test  for  an  excess 
of  preservative.  (Trikresol  being  the  one  most 
employed.)  If  the  mouse  shows  trembling  or  other 
symptoms  of  poisoning  after  subcutaneous  injec- 


CONCENTRATION     OF     SERUM.  187 

tion  of  1  c.c.  of  sernm^  over  0.5  per  cent,  may  be 
suspected. 

Other  toxins  and  bacteria  are  discovered  by 
intraperitoneal  injection  of  gninea-pig. 

For  therapeutic  purposes,  it  is  desirable  to  have 
a  serum  of  high  value  in  order  to  avoid  giving  too 
large  quantities.  Several  diphtheria  serums  are 
on  the  market  which  have  a  value  of  500  units  to 
the  cubic  centimeter.  It  is  difficult  to  immunize 
above  this  point. 

In  some  cases  it  is  desirable  to  concentrate  the 
antitoxic  serum. 

Gibson  has  devised  a  means  for  this  depending 
on  the  fact  that  the  antitoxin  is  closely  associated 
with  or  comprises  the  globulin  of  the  serum.  The 
method  is  as  follows : 

To  from  10  to  15  liters  of  serum,  a  saturated 
solution  of  ammonium  sulphate  is  added  gradually 
until  precipitation  is  complete.  This  filtrate  is 
then  removed  by  filtration  through  paper  and 
dissolved  in  12  liters  of  water.  It  is  then  strained 
through  gauze  to  remove  the  filter  paper.  The 
solution  is  reprecipitated  with  ammonium  sulphate 
and  the  precipitate  removed  as  before.  The 
precipitate  is  then  dissolved  in  24  liters  of  a 
saturated  solution  of  sodium  chlorid  and  filtered 
through  gauze.  This  solution  is  allowed  to  stand 
over  night  and  the  supernatant  fluid  removed  from 
any  precipitate  which  forms.  The  precipitate  is 
washed  with  saturated  sodium  chlorid  and  the 
washing  added  to  the  first  solution. 

The  combined  solutions  are  again  precipitated 
with  saturated  ammonium  sulphate  solution  and 


188  INFECTION     AND     IMMUNITY. 

the  precipitate  collected  on  filter  paper  and  the 
moisture  pressed  partially  out  with  filter  paper. 

The  precipitate  is  then  dialized  in  parchment 
paper  in  running  water  for  three  days,  a  small 
amount  of  chloroform  being  added  as  a  pre- 
servative. 

One-half  of  one  per  cent,  sodium  chlorid  is  then 
added  and  the  solution  filtered  twice  through 
Berkefeld  filters. 

In  a  similar  way  the  U.  S.  Government  has 
provided  for  the  establishment  of  a  legal  tetanus 
antitoxin  unit  and  the  control  of  serum  production. 

Owing  to  the  fact  that  tetanus  toxin  is  very 
stable,  the  toxin  itself  is  kept  for  comparison 
instead  of  the  antitoxin  as  in  diphtheria. 

"The  immunity  unit  for  measuring  the  strength 
of  tetanus  antitoxin  shall  be  ten  times  the  least 
quantity  of  antitetanus  serum  necessary  to  save 
the  life  of  a  350  gram  guinea-pig  for  ninety-six 
hours  asfainst  the  official  test  dose  of  a  standard 
toxin  furnished  by  the  Hygienic  Laboratory  of  the 
Public  Health  and  Marine-Hospital  Service.'^" 

That  the  United  States  government  is  attempt- 
ing to  guard  the  quality  of  antitoxins  on  sale  in 
our  markets  is  apparent  from  the  following  state- 
ment :^ 

"EXAMINATION    OP    SERUMS    MADE    BY    LICENSED 
MANUFACTURERS.* 

"The  act  of  Congress,  approved  July  1,  1902,  entitled 
'An  act  to  regulate  the  sale  of  viruses,  serums,  toxins  and 
analogous  products  in  the  District  of  Columbia,  to  regulate 
interstate    commerce    in    said    articles,    and    for    other    pur- 

7.  Bulletin  No.  43,  Hygienic  laboratory. 

8.  BYom  Rosenau,  "The  Immunity  Unit  for  Standardizing 
Diphtheria  Antitoxin,"  Bulletin  No.  21  of  the  Hygienic 
Laboratory  of  the  Public  Health  and  Marine  Hospital  Service 
of  the  United  States. 


EXAMINATION     OF     SERUMS.  189 

poses,'  and  the  regulations  framed  thereunder,  approved 
Feb.  21,  1903,  imposed  upon  the  director  of  the  Hygienic 
Laboratory  the  duty  of  examining  vaccines  and  antitoxins 
for  purity  and  potency. 

"Accordingly  purchases  are  made  for  the  Hygienic  Lab- 
oratory from  time  to  time  on  the  open  market  by  officers 
of  the  Public  Health  and  Marine-Hospital  Service  stationed 
in  various  parts  of  the  country.  The  antitoxin  is  always 
bought  from  reliable  druggists,  who  keep  the  product  under 
proper  conditions  of  light,  temperature,  etc.  Several  grades 
of  diphtheria  antitoxin  made  by  each  licensed  manufac- 
turer are  bought  and  sent  to  the  Hygienic  Ijaboratory  by 
mail  for  the  purposes  of  these  tests. 

"The  serums  are  tested  not  only  for  potency,  but  also  to 
determine  their  freedom  from  contamination  by  foreign 
bacteria,  and  finally  to  insure  the  absence  of  chemical  poi- 
sons, especially  tetanus  toxin.  Note  is  made  of  the  phys- 
ical appearance  of  the  serum,  and  tests  are  made  to  de- 
termine whether  an  excessive  amount  of  preservative  has 
been   added. 

"A  careful  memorandum  is  made  of  the  facts  given  by 
the  manufacturer,  as  stated  on  the  label,  as  to  the  num- 
ber of  units  contained  in  the  package,  and  the  date  beyond 
which  the  contents  can  not  be  expected  beyond  a  reasonable 
doubt  to  yield  a  specific  result.  Note  is  also  made  of  the 
manufacturer's  compliance  with  the  law  requiring  that  the 
product  be  plainly  marked  with  the  name  of  the  article, 
and  the  name,  address  and  license  number  of  the  manu- 
facturer. 

"Delinquencies  that  occasionally  come  to  light  in  these 
examinations  are  at  once  reported  to  the  Surgeon  General, 
U.  S.  Public  Health  and  Marine-Hospital  Service,  who 
takes  the  necessary  stops  requiring  the  immediate  with- 
drawal of  the  particular  lot  of  serum  from  the  market  and 
institutes  measures  to  prevent  a  repetition  of  similar  errors." 

"SERUM  ANTIDIPHTHERICUM  IN  THE  PHARMA- 
COPEIA. 

"The  next  edition  of  the  United  States  Pharmacopeia, 
being  the  eighth  decennial  revision,  1900,  which  is  to  ap- 
pear shortly,  will  contain  an  antitoxic  serum  for  the  first 
time.  The  serum  will  be  known  officially  as  antidiphtheric 
serum  or  Serum  antidiphthericum,  and  the  unit  will  be 
recognized  as  that  approved  or  established  by  the  United 
States  Public   Health  and  Marine-Hospital   Service. 

"The  official  text,  which  has  been  kindly  furnished  by 
Professor   Remington   in   advance,   will   be  as   follows : 


190  INFECTION     AND     IMMUNITY. 

"SERUM  ANTIDIPHTHERICUM. 

A.NTID1PHTHERIC    SERUM.       DIPHTHERIA    ANTITOXIN. 

"A  fluid  separated  from  tbe  coagulated  blood  of  a  horse 
Equus  caballus,  Linne,  immunized  through  the  inoculation 
of  a  diphtheric  toxin.  It  should  be  kept  in  sealed  glass 
containers,  in  a  riark  place,  at  temperatures  between  4.5° 
and   15°    C.    (40"    and   59°    F.). 

**A  yellowish  or  yellowish-brown,  transparent  or 
slightly  turbid  liquid,  odorless  or  having  a  slight  odor, 
due  to  the  presence  of  the  antiseptic  used  as  a  pre- 
servative. 

"Specific  gravity:  1,025  to  1,040  at  25°  C.   (77°  F.). 

"Antidiphtheric  serum  gradually  loses  its  power,  the 
loss  in  one  year  varying  between  10  per  cent,  and  30 
per  cent.  Each  container  should  be  furnished  with  a 
label  or  statement,  giving  the  strength  of  the  anti- 
diphtheritic  serum,  expressed  in  antitoxic  units,  the 
name  and  percentage  by  volume  of  the  antiseptic  used 
for  the  preservation  of  the  liquid  (if  such  be  used), 
the  date  when  the  antidiphtheric  serum  was  last  tested, 
and  the  date  beyond  which  it  will  not  have  the  strength 
indicated  on  the  label  or  statement. 

"The  standard  of  strength,  expressed  in  units  of  anti- 
toxic power,  should  be  that  approved  or  established  by 
the  United  States  Public  Health  and  Marine-Hospital 
Service. 

"Average  dose  :   3.000  units. 

"Immunizing   dose   for   well   persons :   500   units." 


CHAPTEK  XII. 


toxm. 


THE       STRUCTURE       OF    TOXINS     AND      ANTITOXINS 
AND    THE    NATURE    OF    THE    TOXIN-ANTI- 
TOXIN   REACTION. 

Because  of  the  impossibility  of  obtaining  bac-  Biologic 
terial  toxins  in  pure  form,  no  conception  can  be  ^ 
gained  of  their  composition  in  terms  of  atoms  or 
molecules,  although  it  must  be  assumed  that  they 
have  some  unknown  molecular  structure.  Infer- 
ences as  to  their  nature  and  structure  can  be 
gained  only  by  means  of  the  biologic  experiment, 
i.  e.,  their  effects  on  animals  and  animal  cells 
under  arbitrary  conditions. 

When  a  toxin  and  its  antitoxin  are  mixed  in  ^eutraiiza-^ 
suitable  proportions,  the  mixture  becomes  non-  by  Antiti 
toxic  as  the  result  of  chemical  union  of  the  two 
substances;  each  molecule  of  toxin  has  combined 
with  a  molecule  of  antitoxjn  to  form  a  new  non- 
toxic molecule  which  may  be  spoken  of  as  the 
toxin-antitoxin  molecule.  It  was  at  one  time  sup- 
posed that  antitoxin  had  the  power  of  destroying 
the  toxin,  perhaps  by  a  ferment-like  action.  In 
two  instances  it  has  been  possible  to  show  that 
this  is  not  the  case.  Ordinarily  toxins  are  more 
susceptible  to  heat  than  antitoxins,  but  in  the  case 
of  pyocyaneus  toxin  and  snake  venom  the  anti- 
toxins are  the  more  susceptible.  Wassermann 
found  that  when  a  neutral  mixture  of  pyocyaneus 
toxin  and  its  antitoxin  was  heated  to  a  certain 
temperature  the  mixture  again  became  toxic,  and 
Calmette  made  a  similar  observation  concerning 
venom  and  antivenin.     If  the  toxin  had  been  de- 


192 


INFECTION     AND     IMMUNITY. 


Chemical 
Nature  of 
Reaction. 


Ferments. 


stroyed  by  the  antitoxin  the  solution  certainly 
would  not  have  regained  its  original  toxicity  on 
the  application  of  heat. 

The  following  facts  add  support  to  the  view 
that  neutralization  consists  of  chemical  union  be- 
tween the  two  substances: 

Fii*st,  neutralization  takes  place  according  to 
the  law  of  multiple  proportions,  i.  e.,  ten  times  a 
given  amount  of  antitoxin  will  neutralize  a  pro- 
portionate amount  of  toxin;  second,  neutralization 
is  more  rapid  at  warm  than  at  cold  temperatures; 
and,  third,  more  rapid  in  concentrated  than  in  di- 
lute solutions.  These  are  some  well-known  laws  of 
chemical  reactions. 

"Emil  Fischer  has  shown  that  in  the  ferments, 
definite  atom-gi'oups  of  special  configuration  are 
present  which  above  all  else  are  requisite  for  the 
whole  phenomenon  (of  fermentation).  Only  such 
substances  as  possess  a  group  to  which  the  ferment 
group  corresponds,  as  lock  to  key,  are  subject  to 
the  action  of  a  particular  ferment."  This  applies 
to  the  action  of  a  particular  ferment  on  only  one 
kind  of  substance. 
Haptopiiores.  Having  this  conception  in  mind,  Ehrlich  as- 
sumes that  union  -occurs  between  toxin  and  anti- 
toxin through  a  special  group  of  atoms  which  the 
toxin  molecule  possesses,  and  which  fits  into,  or 
norresponds  specifically  to,  another  group  of  atoms 
in  the  antitoxin  molecule.  These  are  spoken  of 
as  the  binding  or  haptophorous  gi-oups  (hapto- 
phores)  of  the  molecules.  The  haptophorous 
group  of  the  toxin  molecule  is  highly  specific  since 
a  toxin  can  be  neutralized  only  by  its  own  anti- 
toxin, and  naturally  the  haptophorous  group  of 
the  antitoxin  molecule  must  be  equally  specific. 


TOXINS     AND     ANTITOXINS. 


193 


Toxoids. 


The  toxin  molecule  contains  not  only  a  liapto-  Toxopiiore. 
phorous  group,  through  which  it  unites  with  anti- 
toxin in  one  instance  or,  in  another  instance,  with 
tissue  cells  in  the  production  of  disease,  but  also 
certain  constituents  in  which  the  specific  activit}^ 
of  the  substance  resides,  and  by  which  it  produces 
changes  in  tissue  cells,  on  combining  with  them. 
This  functional  or  pathogenic  activity  resides  in 
this  so-called  toxophorous  group  of  the  molecule. 
Hence  the  haptophorous  and  tovophorous  groups 
are  the  two  structural  elements  of  a  toxin  which 
may  be  recognized  by  biologic  experiments. 

It  is  a  peculiarity  of  toxins  that  they  lose  a  cer- 
tain amount  of  their  toxicity  in  the  course  of  time, 
although  their  binding  power  for  antitoxin  remains 
practically  unchanged.  In  the  language  of  the 
terms  which  were  used  above,  the  toxophorous 
groups  may  degenerate  or  disappear  and  leave  the 
haptophorous  groups  intact.  Toxins  which  have 
undergone  this  change  are  called  toxoids. 

Further  evidence  of  the  existence  of  toxoids  lies 
in  the  fact  that  when  used  for  immunization  they 
cause  the  formation  of  antitoxins.  This  is  possi- 
ble only  when  the  substance  is  able  to  unite  with 
the  tissue  cells;  therefore,  the  non-toxic  toxin  or 
toxoid  has  retained  its  haptophorous  groups. 

A  toxin  entirely  free  from  toxoids  has  never 
been  observed,  since  even  during  the  few  days  re- 
quired for  its  preparation  a  certain  amount  of 
degeneration  occurs. 

Additional  information  concerning  the  nature 
of  toxin  has  been  gained  by  experimenting  with 
mixtures  of  toxin  and  antitoxin,  in  which  the  two 
are  present  in  varying  proportions.  This  is  the 
'^partial  saturation"  method  of  Ehrlich.    Through 


Partial 
Saturation 
Metliod  of 
Study. 


194  INFECTION     AND     IMMUNITY. 

a  vast  number  of  experiments  Ehrlich  obtained  in- 
formation which  permitted  liim  to  estimate  that 
200  ^'binding  units'^  are  represented  in  that 
amount  of  diphtheria  toxin  (hypo the tically  pure) 
which  is  exactly  neutralized  by  one  antitoxin  unit. 
If  the  entire  amount  of  antitoxin,  i.  e.,  200/200, 
is  added  to  tlie  quantity  of  toxin  in  question,  com- 
plete neutralization  of  the  latter,  of  course,  occurs. 
In  case  the  toxin  is  entirely  pure,  199/200  of  the 
antitoxin  unit  would  destroy  all  but  1/200  of  the 
initial  toxicity;  and  150/200,  or  100/200,  or 
75/200,  etc.,  of  the  antitoxin  when  added  would 
permit  corresponding  degrees  of  toxicity  to  be 
demonstrated  through  animal  inoculations.  It 
was  found,  however,  that  neutralization  did  not 
take  place  according  to  this  simple  scale.  The  re- 
sults were  complicated,  and  Ehrlich  has  found  it 
convenient  to  express  them  graphically  in  the  form 
The  Toxin  of  ^  "toxiu  spcctrum"^  (Figs.  1,  2,  3  and  4).  For 
Spectrum,  example,  let  199/200  of  the  antitoxin  unit  be 
added  to  the  proper  amount  of  the  toxin,  198/200 
to  another  similar  amount,  197/200  to  another, 
etc.,  down  to  150/200.  In  the  last  mixture,  50 
out  of  the  200  binding  units  which  the  toxin  pos- 
sesses are  free,  and  these  50,  rather  than  some 
other  50,  are  free  because  they  have  less  affinity 
for  the  antitoxin  than  the  150  units  which  were 
Epitoxoi<iN.  bound.  It  has  been  found  that  those  units  which 
first  become  free  have  a  low  degree  of  toxicity.  It 
was  thought  that  they  might  have  lost  their  toxo- 
phorous  groups,  i.  e.,  that  they  were  toxoids;  and 
because  of  their  weak  affinity  for  antitoxin  they 
were  called  epitoxoids.  It  was  found,  however,  that 
they  possessed  a  rather  constant  though  low  degree 
of  toxicity  and  that  the  toxic  action  was  characteris- 


T0X0N8.  195 

tic.  Injection  was  followed  by  some  local  edema,  Toxon. 
then  by  a  long  incubation  period,  and  finally  by 
cachexia  and  paralysis.  On  account  of  this  char- 
acteristic toxic  action  and  the  long  incubation 
period,  Ehrlich  has  concluded  that  the  so-called 
epitoxoid  is  in  reality  a  second  toxin  which  is  se- 
creted by  the  diphtheria  bacillus.  This  he  now 
designates  as  toxon  in  order  to  distinguish  it  from 
that  other  constituent  of  diphtheria  bouillon,  the 
toxin,  which  causes  the  acute  phenomena  of  diph- 
theria. 

The  existence  or  non-existence  of  toxons  has  created 
a  great  deal  of  discussion  among  investigators.  The 
Swedish  chemist,  Arrhenius,  has  recently  attempted  to 
apply  certain  principles  of  physical  chemistry  to  the 
study  of  toxins  and  antitoxins.  It  is  a  well-known  fact 
that  some  chemical  substances,  when  in  solution,  have 
the  power  of  breaking  up  into  their  constituent  parts; 
thus  sodium  chlorid  breaks  up  in  part  into  sodium  and 
chlorin,  as  sodium  or  chlorin  ions  or  electrolytes.  The 
dissociated  sodium  or  chlorin  may  then  enter  into  com- 
bination with  any  other  suitable  substances  which  may 
be  present.  Arrhenius  holds  that  this  is  the  case  with 
the  toxin-antitoxin  molecule,  that  it  may  to  a  certain 
extent  again  break  up  into  separate  toxin  and  antitoxin. 
He  believes  that  this  dissociated  toxin  is  the  substance 
which  Ehrlich  has  been  callmg  toxon.  Madsen,  who 
formerly  had  done  much  work  with  toxons,  has  now 
joined  with  Arrhenius  in  support  of  the  dissociation 
theory.  Bordet  believes  that  toxon  and  the  various 
other  constituents  of  toxin  described  by  Ehrlich  as 
separate  substances,  are  the  result  of  combinations  of 
varying  proportions  of  toxin  and  antitoxin.  He  pro- 
duced comparable  phenomena  by  mixtures  of  complement 
and  anticomplement  in  varying  proportions  and  noting 
the  degree  of  hemolysis  produced  on  sensitized  corpus- 
cles.    In  spite  of  the  reasonableness  of  this  theory,  Ehr- 


196  INFECTIOy     AND     IMMUNITY. 

lich  and  his  followers  continue  to  uphold  the  toxon  as 
an  independent  toxic  substance,  and  have  published 
additional  experiments  to  support  their  position. 

protoxoids.  Let  One  now  add  still  smaller  amounts  of  the 
antitoxin  unit  to  the  200  binding  units  of  the 
toxin.  When  149/200  are  added  it  is  found  that 
a  certain  amount  of  true  toxin  remains  free,  the 
quantity  which  is  unbound  being  in  direct  propor- 
tion to  the  amount  of  antitoxin  withheld.  Conse- 
quently when  but  50/200  antitoxin  unit  is  added 
the  amount  of  free  toxin  corresponds  to  100  bind- 
ing units.  If  true  toxin  only  remained  it  could 
then  be  said  that  the  constitution  of  this  toxin  is : 
toxin  150  and  toxon  50.  However,  it  may  be 
found  that  as  49/200,  48/200,  etc.,  to  0/200  anti- 
toxin unit  are  added,  no  increase  of  free  toxin  is 
found,  although  the  antitoxin  added  has  been 
bound.  In  this  case,  the  50  binding  units  of  toxin 
which  have  the  greatest  affinity  for  antitoxin  are 
non-toxic;  i.  e.,  they  are  toxoids,  and  since  they 
have  the  maximum  affinity  for  antitoxin  they  are 
called  protoxoids. 

syntoxoia.M.  It  has  been  assumed  also  that  a  toxoid  may 
exist  which  has  an  affinity  for  antitoxin  exactly 
equaling  that  which  toxin  possesses;  this,  as  yet 
purely  hypothetical  constituent,  bears  the  name  of 
syntoxoid. 

Figure  1  is  a  graphic  representation  of  the 
toxin  just  described  (Madsen).  Probably  no  two 
toxins  have  the  same  constitution.  The  toxon 
zone,  for  example,  could  well  be  much  larger  in 
one  diphtheria  toxin  than  in  another. 

Refinements  in  experimentation  show  that  even 
the  true  toxin  is  not  uniform  in  its  virulence  and 
its   affinity   for  antitoxin.     Accordingly  a   proto- 


Proto-,    Den- 

tero-   and 

Trltotoxinn. 


7'0A7iY     SPECTRA. 


197 


Prototo^ot<i 


Tc 


oxone 


T— T ,  ,         y  ■   ^  ■   lyi    ■,■    I  ^    i  ,1 ,1   r    ).<•,!    '  1*   'y 1        «        I         « 

0    /«     *o     Jo     YO     JO     4«    7«    to    9*  m  110    /*0   /»o    /yj  /<•© /{O  /7»  /f#  fft  X*it 

Figure    1. 


Figure    2. 


JJeutrro-      ~r    -t    *  •  •, 


e   or 


Figure    3. 


^eurero-     TntoUxin      0 
Figure    4. 

Figures  1,  2,  3  and  4  are  taken  from  Aschoff's  "Ehr- 
lich's  Seitenkettentlneorie,  etc.,"  Ztschr.  f.  Allgem.  Physiol., 
vol.  i,  1902.  Figure  1  is  a  toxin  spectrum  worked  out  by 
Madsen.  Figures  2,  3  and  4  are  spectra  representing  the 
changes  in  qualitative  and  quantitative  structure  which  a 
toxin  may  undergo  with  age,  as  described  in  preceding  para- 
graphs. 


198  INFECTION     AND     IMMUNITY. 

toxin,  a  deuterotoxin  and  a  tritotoxin  may  be  rec- 
ognized by  this  same  partial  saturation  method. 
(See  Fig.  2.)  For  example,  it  may  be  found  that 
when  a  portion  of  the  antitoxin  unit,  between  the 
limits  of  149/200  and  125/200,  is  withheld,  a 
toxin  is  left  free  which  is  less  virulent  than  that  re- 
maining free  between  the  limits  of  124/200  and 
100/200 ;  and  from  this  point  on  the  new  unbound 
toxin  may  be  still  more  virulent.  The  first  would 
be  tritotoxin,  the  second  deuterotoxin  and  the 
third  prototoxin. 

The  "spectrum"  of  a  toxin  changes  with  its  age. 
The  prototoxin,  and  portions  of  the  deutero-  or 
tritotoxin  may  disappear  because  of  toxoid  forma- 
tion. Such  changes  have  led  to  the  recognition  of 
an  alpha  and  a  beta  modification  of  the  toxin. 
The  alpha  modifications  of  all  three  toxins  readily 
become  toxoids.  Only  the  beta  modification  of  the 
deuterotoxin  remains  constant.  The  toxon  also 
remains  relatively  intact  (Figs.  2,  3  and  4). 

This  very  complicated  method  of  investigation 
was  also  undertaken  by  Madsen  in  the  study  of 
tetanus  toxin,  for  which  a  somewhat  similar 
"spectrum"  was  constructed. 

Such  spectra  have  not  been  worked  out  in  de- 
tail for  some  of  the  vegetable  toxins,  as  ricin  and 
abrin,  but  it  is  known  that  they  form  toxoids. 

Some  of  the  toxins  of  snake  venom  differ  from 
the  bacterial  toxins  in  structure  (pages  428-431). 
The  Forma-  The  idea  was  originally  advanced  that  antitoxin 
AntVto^in!  IS  transformed  toxin,  a  change  in  the  latter  hav- 
ing been  effected  through  some  action  of  the 
tissues.  In  that  case,  the  amount  of  antitoxin  pro- 
duced should  be  roughly  equivalent  to  the  amount 
of  toxin  injected.     This,  however,  was  found  not 


SIDE-CHAIN     THEORY. 


199 


to  be  the  case.  A  single  injection  of  tetanus  toxin 
may  yield  100^000  times  the  amount  of  antitoxin 
necessary  to  neutralize  the  toxin  injected.  An  in- 
teresting experiment  is  on  record  which  shows  the 
fallacy  of  the  view  just  mentioned.  An  animal, 
tlie  serum  of  which  was  rich  in  antitoxins,  was 
bled  repeatedly  until  an  amount  of  blood  which 
equalled  the  total  quantity  normally  present  in  the 
animaPs  body  was  drawn.  Yet  the  antitoxic 
power  of  the  new  formed  blood  was  practically  un- 
changed. 

Metchnikoff,  to  explain  this  "overproduction" 
of  antitoxin,  has  suggested  that  the  toxin  molecules 
may  be  taken  up  by  phagocytic  cells  and  broken  up 
into  an  indefinite  number  of  smaller  molecules, 
each  of  which  then  is  altered  in  some  obscure  man- 
ner so  as  to  constitute  a  molecule  of  antitoxin. 

The  views  of  Ehrlich  have  found  wide  accept- 
ance, and  have  provided  a  valuable  working  hy- 
pothesis for  many  investigations.  A  considera- 
tion of  this  subject  introduces  one  at  once  to  the 
well-known  side-chain  theory  of  immunity  of 
Ehrlich.  It  may  be  considered  briefly  at  this  point, 
in  so  far  as  it  involves  the  origin  and  nature  of 
antitoxin.  Ehrlich  considers  it  fundamental,  in 
regard  to  the  metabolic  activity  of  cells,  to  assume 
that  the  cell  constituents  must  enter  into  chemical 
combination  with  food  substances  in  order  that  the 
latter  may  be  made  available  for  the  use  of  the 
cell.  It  is  supposed  that  cells  contain  cer- 
tain atom  groups  of  unknown  chemical  nature 
which  make  possible  the  binding  of  food  sub- 
stances. The  name  of  receptor  was  given  to  such 
groups,  since  substances  are  received  into  the  cell 
through  them.    -Inasmuch  as  the  foods  and  some 


Ehrlicli's 
"Side-Chain." 


Receptors. 


209  INFECTION     AND     IMMUNITY. 

Multiplicity  other  substaiices  wliich  penetrate  the  cells  differ 
in  their  chemical  nature,  it  is  probable  that  there 
are  various  receptors  for  the  various  types  of  sub- 
stances. The  binding,  however,  is  but  a  prelimi- 
nary step  to  profound  changes  which  the  substance 
may  next  undergo,  through  the  action  of  other, 
more  vital,  cell  constituents.  That  is  to  say,  the 
receptor  is  but  a  link  to  bring  the  substance  into 
relationship  with  the  vital  activities  of  the  cell, 
which  Ehrlich  supposes  may  reside  in  a  hypotheti- 
cal "LeistungsJtern"  (action  center  or  nucleus). 
In  view  of  this  conception  one  readily  understands 
the  propriety  of  considering  the  receptor  as  a  side- 
chain  of  the  ''Leistungshern/'  just  as  the  chemist 
speaks  of  the  various  groups  which  may  be  at- 
tached to  the  benzol  ring,  or  benzol  nucleus,  as 
side-chains  (See  Chapter  XIX). 
Action  of  In  preceding  pages  it  has  been  emphasized  that 
a  toxin,  in  order  that  it  may  injure  a  cell,  must 
enter  into  chemical  combination  with  its  constitu- 
ents, and  it  is  a  fundamental  tenet  of  the  Ehrlich 
theory  that  this  union  is  one  which  takes  place 
between  the  toxin  and  a  cell  receptor  (side-chain). 
The  cell  receptor,  then,  either  is  a  haptophore  or 
possesses  a  haptophore  as  a  part  of  its  complex. 

As  the  physiologic  demands  are  probably  re- 
sponsible for  the  character  of  the  various  recep- 
tors, it  is  not  likely  that  special  receptors  are 
created  when  some  unusual  substance,  as  a  bac- 
terial toxin,  is  introduced  into  tlie  body.  Conse- 
quently, when  toxin  unites  with  a  cell,  it  probably 
occupies  receptors  which,  under  normal  circum- 
stances, are  employed  in  some  physiologic  process. 
If  some  inert,  non-toxic  substance  should  com- 
bine extensively  with  cells,  a  corresponding  num- 


RECEPTORS. 


201 


ber  of  receptors,  which  ordinarily  are  used  for 
normal  metabolism,  would  be  thrown  out  of  func- 
tion. Union  of  this  nature  would  be  equivalent 
to  an  injury  of  the  cell,  and  it  is  possible  that  the 
action  of  toxoids  is  of  this  mild  nature. 


«' 

^ 

'  r 

f^  

5 

"1\ 

i 

-\ 

\  1 

.  \ 

f  J 

111 

[  1 

\  \ 

'   J    ' 

u 

,     ] 

''  \ 

-' 

Fig.  5. — Graphic  representation  of  receptors  of  the  first 
order  and  of  toxin  uniting  with  the  cell  receptor,  a.  Cell 
receptor ;  &,  toxin  molecule ;  c,  haptophore  of  toxin  mole- 
cule ;  (L,  toxophore  of  toxin  molecule ;  e,  haptophore  of  the 
cell  receptor.  From  Ehrlich's  "Schlussbetrachtungen," 
Nothnagel's  System  of  Medicine,  vol.  viii.  This  cut  is  not 
to  be  taken  as  representing  the  actual  morphology  of  toxins 
or  cell  receptors.  Nothing  is  known  of  their  morphology, 
if,  indeed,  they  havef  any.  The  cut  is  intended  merely  to 
represent,  in  a  graphic  manner,  the  supposed  chemical 
structure  and  mode  of  action  of  these  substances.  This 
statement  applies  also  to  Figures  6  and  7. 

When  toxin  unites  with  cells  there  is  involved 
not  only  the  diversion  of  cell  receptors  from  their 
customary  functions,  but  in  addition  the  destruc- 
tive action  of  the  toxin  on  the  vital  parts  of  the  cell 


202  INFECTION     AND     IMMUNITY. 

(perhaps  on  the  ''Leistungshem").  The  more 
toxin  introduced,  the  greater  the  number  of  cell 
receptors  bound,  and  the  greater  the  injury  to  the 
celL 
Hypothesis  In  casc  a  non-fatal  amount  of  toxin  has  been 
bound,  but  sufficient  to  cause  some  injury,  how 
does  the  cell  respond  to  the  injury?  Weigert,  a 
few  years  ago,  gave  expression  to  a  hypothesis 
which  is  held  to  have  some  bearing  on  this  ques- 
tion. In  studying  regeneration  following  injury 
he  concluded  that  tissues  have  the  tendency  to 
reproduce  not  only  to  the  extent  of  making  good 
tlie  injury,  but  that  an  excess  of  new  tissue  re- 
sults. The  clearest  example  of  this  occurrence  is 
that  of  scar  formation,  in  which  a  seeming  excess 
of  new  connective  tissue  cells  is  formed, 
which  later  disappears  in  part.  Similarly,  when 
a  non-fatal  amount  of  toxin  unites  with  the 
overproduc-  rcceptors,  a  cell  defect  or  injury  is  created.  The 
side-chtTins*  ccll  has  for  practical  purposes  lost  so  many  recep- 
tors. This  loss  affects  the  vital  activities  of  the 
cell,  the  "LeistungsTcern,"  and  new  receptors,  iden- 
tical with  those  occupied,  are  reproduced.  Follow- 
ing the  law  stated,  they  are  reproduced  in  excess 
of  the  number  injured,  and  the  excess  may  be  so 
great  that  the  cell  may  be  overfilled  with  them — 
so  overfilled  that  many  are  discharged  and  reach 
the  general  circulation.  These  cast-off  receptors, 
or  side-chains,  still  retaining  their  power  of  unit- 
ing "uith  toxin,  constitute  our  antitoxins.  As 
Behring  has  stated  it,  the  receptor,  when  attached 
to  the  cell,  is  the  agent  through  which  the  latter 
is  attacked,  but  when  cast  off  from  the  cell  becomes 
its  protector  (Fig.  5). 


ANTITOXINS.  203 

As  regards  the  structure  of  the  antitoxin  (cast-  Receptors  of 
off  receptor),  it  is  necessary  to  assume  only  the  order.'*** 
presence  of  the  proper  haptophorous  group.  Ehr- 
lich  designates  all  receptors  of  this  simple  type  as 
"receptors  of  the  iirst  order."  In  following 
sections  we  will  have  to  do  with  receptors  of  the 
second  and  third  orders. 

Wassermann  gives  the  following  list  of  anti- 
toxins : 

ANTITOXINS  FOR  BACTERIAL  TOXINS. 

Diphtheria  antitoxin. 

Tetanus  antitoxin. 

Botulism  antitoxin. 

Pyocyaneus  antitoxin. 

Symptomatic  anthrax  antitoxin. 

Antileucocidin,  an  antitoxin  for  the  leucocytic 

poison  of  the  staphylococcus. 
Antitoxins  for  the  blood  dissolving  toxins  of  a 

number  of  bacteria. 

ANTITOXINS  FOR  ANIMAL  TOXINS. 

Antivenin  for  snake  poison. 
Antitoxin  for  scorpion  poison. 
Antitoxin  for  spider  poison. 
Antitoxins  for  certain  poisons  of  fish,  eel  serum, 
salamander^  turtle,  and  for  wasp  poison. 

ANTITOXINS  FOR  PLANT  TOXINS. 

Antiricin,  for  a  red  blood  corpuscle  poison  of 

the  castor  oil  bean. 
Antiabrin,  for  a  similar  poison  of  the  jequirity 

bean. 
Antirobin,  for  robin,  a  locust  tree  poison. 
Anticrotin,  for  crotin,  a  toxin  from  the  bean  of 

Croton  tiglium,  the  croton  oil  bean. 


204  INFECTION     AND     IMMUNITY. 

Hay  fever  antitoxin,  for  the  toxin  of  pollens 
which  cause  hay  fever. 

ANTIFERMENTS. 

Antirennet. 

Antipepsin. 

Antitrypsin. 

Antiiibrinferment. 

Antiurease,  for  urease,  a  urea  splitting  ferment. 

Antilaccase. 

Antityrosinase. 

Antisteapsin. 

Antiferments  for  the  ferments  of  bacterial 
cultures. 

The  above  are  true  antitoxins.  There  are  otheT* 
substances,  however,  which  occasionally  exert  an 
antagonistic  action  on  toxins,  although  they  prob- 
ably are  not  true  antitoxins.  For  example,  it  has 
been  found,  that  cholesterin  neutralizes  the  action 
of  tetanolysin,  the  hemolytic  toxin  of  the  tetanus 
bacillus  (Noguchi),  and  also  the  hemolytic  action 
of  cobra  venom  and  cobra-lecithid.  (See  Chap. 
XVI).  On  the  other  hand,  it  does  not  affect  two 
other  hemolytic  toxins,  staphylolysin,  which  is 
derived  from  the  staphylococcus,  and  arachuolysin 
which  is  obtained  from  spiders  (Kyes),  the  action 
of  cholesterin,  therefore,  is  in  no  sense  specific  and 
apparently  is  of  a  different  type  from  that  of 
serum  antitoxins.  This  is  further  indicated  by 
the  fact  that  chloesterin  also  inhibits  the  hemolytic 
activity  of  certain  substances  which  can  not  be 
classed  with  the  toxins,  e.  g.  saponin,  agaricin 
(Noguchi).  Fluids  which  contain  cholesterin  nat- 
urally, as  milk,  serum  and  bile,  have  a  similar 
inhibiting  power. 


ANTITOXINS.  205 

The  discovery  of  Hcktoen  that  certain  salts  are 
able  to  neutralize  the  toxic  action  of  some  serums, 
by  combining  with  the  so-called  complement,  may 
also  be  mentioned  in  this  connection. 


CHAPTER  XIII. 


Specificity. 


Widal  and 
Grnnljaui»i. 


Normal 
Agreintinins. 


THE  PHENOMENON  OF  AGGLUTINATION. 

Agglutination,  in  the  bacteriologic  sense,  refers 
to  the  clumping  and  sedimentation  of  a  homogene- 
ous suspension  of  micro-organisms  by  the  action  of 
a  serum. 

Although  a  number  of  investigators  had  ob- 
served the  phenomenon  of  agglutination,  Gruber 
and  Durham  first  saw  its  significance.  They  found 
that  the  reaction  was  a  specific  one,  i.  e.,  that  the 
serum  which  would  cause  the  strongest  agglutina- 
tion of  a  micro-organism  was  that  of  an  animal 
which  had  been  made  immune  to  it  by  repeated 
injections. 

Widal's  service  consisted  in  the  utilization  of  the 
phenomenon  as  an  aid  in  the  diagnosis  of  typhoid 
fever.  He  is  the  originator  of  clinical  serum 
diagnosis.  It  is  perhaps  largely  a  matter  of  acci- 
dent that  we  speak  of  the  Widal  reaction  rather 
than  the  Griinbaum  reaction.  Grunbaum  was  car- 
rying on  the  same  work  at  the  same  time,  but 
Widal  preceded  him  in  the  publication  of  his  more 
extensive  work. 

In  the  chapter  on  natural  immunity  it  was 
stated  that  normal  serums  often  are  able  to  ag- 
glutinate bacteria.  Normal  human  serum  may  ag- 
glutinate the  typhoid,  colon,  pyocyaneus,  and  dys- 
entery bacilli,  and  occasionally  the  staphylococcus 
and  cholera  vibrio;  it  does  not  agglutinate  the 
streptococcus  and  some  other  organisms.  In  cer- 
tain cases  it  may  agglutinate  the  typhoid  bacillus 


IMMUNE     AGGLUTININS. 


207 


une 
Agrslntinins. 


even  when  the  serum  is  diluted  to  one  in  thirty,  a 
point  of  practical  importance  in  the  clinical  use  of 
the  test.  When  a  normal  serum  is  found  to  have  a 
high  agglutinating  power,  a  previous  infection  by 
the  micro-organism  is  to  be  thought  of.  This  pos- 
sihility  receives  emphasis  from  the  fact  that  the 
serum  of  a  new-born  child  is  devoid  of  many  of  the 
agglutinins  which  are  found  in  later  life.  Hence, 
of  the  so-called  normal  agglutinins,  many,  after 
all,  may  be  acquired  properties. 

The  term^  immune  agglutinin  is  applied  to  the  imm 
agglutinating  substance  in  a  serum,  when  the 
property  has  developed  as  a  result  of  infection,  or 
of  systematic  immunization  with  the  organism. 
Thoy  are  formed  during  infections  with  the  organ- 
isms of  typhoid,  cholera,  dysentery,  plague,  etc. 

For  the  artificial  production  of  agglutinins,  the 
bacteria  may  be  injected  into  the  veins,  subcutane- 
ous tissue,  or  peritoneal  cavity ;  in  some  cases  they 
may  be  fed  to  animals,  rubbed  into  the  skin,  or 
sprayed  into  the  lungs.  If  certain  micro-organ- 
isms are  sealed  up  in  a  collodion  sac  and  placed  in 
the  abdominal  cavity  of  an  animal,  an  agglutinat- 
ing serum  will  be  formed ;  the  necessary  substances 
diffuse  through  the  sac  and  reach  those  body  cells 
which  produce  the  agglutinin.  It  is  not  necessary 
that  living  bacteria  be  injected ;  in  fact,  the  strong- 
est agglutinin  is  said  to  be  formed  by  the  injection 
of  bacteria  which  have  been  killed  by  a  tempera- 
ture of  62  C.  In  certain  instances  agglutinins  are 
produced  by  immunization  with  disintegration 
products  of  bacteria  or  with  bacterial  extracts. 

Nearly  all  bacteria,  even  when  non-pathogenic,   Ag-sintinin- 
will  give  rise  to  agglutinating  serums  when  in- 
jected; but  not  all  have  the  power  equally.  ISTicolle 


Producing 
Orgranisms. 


208  IXFECTION     AXD     IMMUNITY. 

and  Trenell  distinguish  three  groups  of  bacteria 
in  regard  to  their  agglutinabilit}^  by  the  homolo- 
gous antiserums.^  The  first  group  includes  easily 
agglutinable  organisms,  for  the  most  pathogenic: 
Typhoid,  dysentei*}^,  cholera,  plague,  glanders,  and 
the  colon,  psittacosis,  pyocyaneus  bacilli,  and  B. 
enteritidis.  They  yield  agglutinating  serums  read- 
ily either  as  a  result  of  infection  or  by  immuniza- 
tion. The  second  group  comprises  organisms 
which,  during  infection  or  convalescence,  do  not 
cause  the  formation  of  agglutinins,  but  may  be 
forced  to  do  so  by  systematically  injecting  them 
into  animals.  In  the  third  group  are  included 
those  which  even  during  prolonged  immunization 
rarely  cause  the  formation  of  agglutinating 
serums:  the  Friedlander  bacillus.  These  facts 
may  be  taken  as  an  index  of  the  diseases  in  which 
we  may  expect  to  obtain  the  agglutination  reaction 
by  the  serum  of  the  patient. 
Variations^  in  The  degree  of  agglutinating  power  which  may 
jB:enic  Power  be  obtained  by  immunization  varies  greatly.  Van 
rganisntN.  ^^^  Yeldc  spcaks  of  a  typhoid  serum  which  in  a 
dilution  of  one  in  one  million  was  agglutinating, 
and  Durham  had  a  cholera  serum  which  was  ef- 
fective in  a  dilution  of  one  in  two  millions.  Such 
powerful  serums  are  rarely  obtained. 

Even  two  different  strains  of  the  same  organism 
may  differ  in  their  ability  to  cause  the  formation 
of  agglutinins.  It  is  generally  said  that  a  typhoid 
strain,  which  is  agglutinated  with  difficulty,  gives 
rise  to  a  weak  agglutinating  serum,  while  an  easily 

].  The  homologous  organism  for  a  typhoid  serum,  for  ex- 
ample, is  the  typhoid  bacillus,  and  vice  versa  ;  other  organ- 
isms, or  other  serums,  are  heterologous.  These  are  commonly 
used  terms. 


AGGLUTININS. 


209 


agglutinable  strain  gives  a  strong  agglutinin.  The 
logic  of  this  will  become  apparent  when  we  con- 
sider the  nature  of  the  bacterial  substance  which 
causes  the  body  to  produce  agglutinin. 

That  the  agglutinating  power  of  the  scrum  of  a  variations  in 
typhoid  patient  varies  from  day  to  day  is  a  fact  A^SruUnins. 
of  practical  importance.  It  may  be  thirty  times  as 
strong  one  day  as  the  next,  and  may  even  disap- 
pear entirely  for  a  day  or  two.  Hence  the  impor- 
tance of  making  more  than  one  test  in  a  suspicious 
case,  when  the  first  trial  has  been  doubtful  or 
negative.  There  is  no  adequate  explanation  for 
this  great  variation.  It  is  said  that  mixed  infec- 
tions, intestinal  hemorrhage,  or  a  sudden  pouring 
out  of  typhoid  bacilli  into  the  circulation  may 
cause  a  reduction  in  the  agglutinating  power.  This 
occurrence  has  an  important  bearing  on  the  possi- 
bility of  using  the  agglutinating  power  of  the 
serum  as  a  prognostic  sign.  Although  it  has  often 
been  noted  that  in  fatal  infections  agglutinins  may 
be  absent  from  the  serum,  the  variations  just  men- 
tioned indicate  that  prognosis  could  not  be  based 
safely  on  the  result  of  a  single  agglutination  test. 

The  agglutinating  substance  is  found  in  the  oistriijTition 
highest  concentration  in  the  blood  serum,  but  it  ins  in  Body. 
may  be  demonstrated  in  the  various  body  fluids 
and  in  extracts  of  the  organs ;  it  is  said  to  be  par- 
ticularly rich  in  the  milk.  It  is  present  in  the 
serum  of  an  artificially  produced  blister,  and  it  has 
been  recommended  that  blistering  be  resorted  to 
in  order  to  obtain  serum  for  the  test.  The  bile 
often  agglutinates  the  t3rphoid  bacillus,  but  the 
power  has  no  necessary  relationship  to  a  pre-exist- 
ing infection ;  it  is  possible  that  the  agglutination 
in   this   case  is   due  to   obscure  chemical   causes 


210  INFECTION     AND     IMMUNITY. 

rather  than  to  the  usual  serum  agglutinin.  Becht 
and  Greer  find  that  agglutinins  occur  in  the  var- 
ious body  fluids  in  the  following  order  of  concen- 
tration :  blood  serum,  thoracic  lymph,  neck  lymph, 
traces  in  the  pericardial  fluid,  least  and  not  con- 
stantly in  the  cerebrospinal  fluid  and  aqueous 
humor.  The  administration  of  pilocarpin  causes 
a  rise  in  the  agglutinating  power  of  the  tears, 
sputum  and  some  other  body  fluids;  the  drug 
increases  cell  secretions. 
Inheritance.  When  typhoid  fcver  occurs  during  pregnancy, 
agglutinins  may  appear  in  the  serum  of  the  fetus. 
On  the  one  hand  it  has  been  held  that  agglutinin 
passes  from  the  mother  to  the  fetus,  or,  on  the 
other  hand,  that  the  presence  of  agglutinins  arises 
from  infection  of  the  fetus  itself. 

Although  the  milk  may  be  very  rich  in  agglu- 
tinin, it  is  doubtful  if  the  serum  of  a  breast-fed 
child  undergoes  much  increase  in  its  agglutinating 
power  because  of  the  ingestion  of  the  milk.  The 
intestinal  juices    (trypsin)    digest  agglutinins. 

The  origin  of  agglutinins  in  the  animal  body  is, 
according  to  very  convincing  experiments  of 
Hcktoen  and  Carlson,  the  tissue  cells  of  the  body. 
Significance  One  of  tlic  most  interesting  and  important  phe- 
nat?on'  uomcua  in  the  study  of  immunity  is  the  so-called 
Pfeiffer  phenomenon.  An  animal  which  has  been 
rendered  immune  to  cholera  by  repeated  injections 
of  cholera  vibrios  has  the  power  of  digesting  or  dis- 
solving th^  latter  when  they  are  placed  in  the  fresh 
set-um  or  in  the  peritoneal  cavity  of  the  immunized 
animal.  Gruber  and  Durham  were  studying  this 
phenomenon  in  the  test  tube  when  they  first  ob- 
served the  agglutination  reaction.     It  was  found 


AGGLUTINATION.  211 

that  the  agglutinating  property,  as  well  as  the  bac- 
tericidal power,  was  the  resuil:  of  immunization. 
Inasmuch  as  an  increase  in  the  bactericidal  power 
of  a  serum  points  to  the  existence  of  an  acq  aired 
immunity,  the  question  naturally  arises:  Does  the 
associated  property  of  agglutination  have  a  similar 
significance  ? 

Many  observations  indicate  that  the  two  activi- 
ties are  distinct,  that  they  depend  on  different 
substances  in  the  serum.  The  following  are  the 
important  points  involved: 

1.  The  bactericidal  power  is  destroyed  at  56  C, 
while  agglutinins  resist  a  temperature  of  62  C. 

2.  In  certain  cases  it  has  been  possible  to  cause 
the  bacteria  to  absorb  the  agglutinin  from  the 
serum,  leaving  the  bactericidal  substance  intact. 

3.  A  serum  may  be  bactericidal,  but  not  agglu- 
tinating. 

4.  During  the  course  of  natural  or  experimental 
typhoid  fever  or  cholera  the  development  of  the 
agglutinating  and  bactericidal  powers  may  not  be 
parallel.  In  cholera,  the  agglutinating  power  may 
disappear  soon,  but  the  bactericidal  power  remains 
for  a  long  time. 

5.  Micro-organisms  which  have  been  killed  by  a 
bactericidal  serum  may  lose  their  toxicity;  ag- 
glutinated bacteria   remain  virulent. 

Besredka  found  an  apparent  relationship  be- 
tween agglutination  and  immunity;  if  typhoid 
bacilli  were  agglutinated  before  they  were  injected 
into  the  abdomen  of  a  guinea-pig  the  animal  would 
recover,  but  if  thev  were  not  as^sflutinated  death 
resulted.  The  explanation  offered  for  this  loss  of 
virulence  is  that  the  bacilli  being  agglutinated  and 
immobilized   are   more   readily   taken   up   by   the 


212 


IXFECTION     AND     IMMUyiTY. 


Technic    of 

the     Agrgluti- 

nation   Test. 


The    Bacterial 
Suspension. 


phagoc3'tes;  if  phagocytosis  is  inhibited  by  some 
means  the  agglutinated  organisms  are  found  to  be 
still  virulent. 

Koch  has  attempted  to  use  the  agglutination 
test  with  the  tubercle  bacillus  as  an  index  of  im- 
munity against  tuberculosis.  This  is  not  accepted 
as  a  reliable  test  for  the  immunity,  but  is  perhaps 
a  general  index  of  the  ability  of  the  individual  to 
form  antibodies  for  this  organism.  This  method 
was  devised  inasmuch  as  the  bactericidal  action  of 
a  serum  on  the  tubercle  bacillus  is  not  readily  de- 
termined. 

One  may  use  two  methods  of  determining  the 
agglutination  of  bacteria  :  1.  the  macroscopic  or 
naked  eye  observation  of  the  clumping  and  sedi- 
mentation of  a  homogeneous  suspension  of  the 
bacteria  in  test-tubes;  2,  the  microscopic  observa- 
tion of  the  clumping  of  the  organisms  when  the 
latter  are  mixed  with  serum  and  mounted  as  a 
"hanging-drop"  preparation." 

AVhen  the  organism  to  be  tested  grows  rapidly, 
it  is  the  custom  to  use  a  young  culture,  one  which 
has  grown  on  an  agar  surface  or  in  bouillon  for 
from  eighteen  to  twenty-four  hours.  Older  cul- 
tures of  the  typhoid  bacillus  or  of  the  cholera 
vibrio  are  agglutinated  with  more  difficulty  than  a 
young  culture.  If  an  agar  culture  is  used,  the 
bacteria  may  be  washed  from  the  surface  by  pour- 


2.  For  .1  hanging-drop  preparation  it  is  necessary  to  have 
a  slide  with  a  saucer-shaped  depression  on  one  surface.  A 
drop  of  the  solution  to  be  examined  is  mounted  on  a  cover 
glass,  and  the  latter  Is  then  mounted,  drop  side  down,  over 
the  depression  and  the  edges  of  the  cover-glass  sealed  with 
vase! in  or  paraffin.  There  Is  ample  room  for  motile  organ- 
isms to  swim  about  in  such  a  preparation,  and  the  loss  of 
motility   incident  to  agglutination   is  readily  observed. 


BACTERIAL     SUSPENSIOIS'.  213 

ing  5  or  10  c.c.  of  physiologic  salt  solution  into 
the  tube  and  shaking  vigorously;  the  resulting 
suspension  is  then  ready  for  use.  For  either  the 
macroscopic  or  microscopic  test  it  is  absolutely 
essential  to  have  a  homogeneous  suspension  of  the 
bacteria^  in  order  to  avoid  misinterpretations  which 
may  be  occasioned  by  the  accidental  or  natural 
bacilli  were  agglutinated  before  they  were  injected 
should  be  shaken  thoroughly  before  the  emulsions 
are  used.  This  uniformity  of  suspension  is  readily 
accomplished  with  such  organisms  as  the  typhoid 
bacillus  and  cholera  vibrio^  motive  organisms,  but 
when  they  grow  in  chains  (streptococcus)  or  in 
coherent  masses  (diphtheria  and  tubercle  bacilli) 
more  violent  measures  must  be  resorted  to.  Daily 
shaking  of  a  liquid  culture  of  the  diphtheria  or 
tubercle  bacillus  is  fairly  effective,  but  the  medium 
must  be  passed  through  a  paper  filter  before  it  can 
be  used  safely;  in  this  way  the  larger  clumps  are 
removed.  Some  investigators  dry  a  large  quantity 
of  tubercle  bacilli,  grind  them  up  thoroughly  in  an 
agate  mortar  and  suspend  the  particles  in  salt 
solution;  the  fragmented  condition  of  the  organ- 
isms does  not  interfere  with  their  participation  in 
the  reaction.  One  should  have  a  uniform  technic 
in  preparing  a  bacterial  emulsion  in  order  to  obtain 
as  nearly  as  possible  the  same  number  of  bacteria 
in  a  given  volume  of  solution,  on  different  occa- 
sions. For  example,  one  may  uniformly  suspend 
a  twenty-four-hour  agar  culture  in  10  c.c.  of  salt 
solution.  A  uniform  technic  makes  it  possible  to 
observe  the  quantitative  relationship  which  exists 
between  the  mass  of  bacteria  to  be  agglutinated 
and  the  agglutinating  power  of  the  serum. 


214  INFECTION     AND     IMMUNITY. 

To  Obtain  To  obtain  serum  for  the  test  one  may  resort  to 
blistering;  place  a  cantharides  plaster  from  one- 
half  to  three-fonrths  of  an  inch  square  on  the  ab- 
dominal skin,  protect  it  with  a  dressing,  and  in 
about  twelve  hours  remove  the  serum  with  a  steril- 
ized hypodermic  syringe.  Or,  one  may  collect  in  a 
small  test  tube  from  0.5  to  1  c.c.  of  blood  from  the 
lobe  of  the  ear  or  finger-tip,  and  draw  off  the  serum 
after  it  has  separated  by  clotting.  It  is  the  cus- 
tom in  some  well-equipped  laboratories  to  fill  sev- 
eral U-shaped  capillary  tubes  with  blood  from  the 
lobe  of  the  ear  and  to  separate  the  blood  from  the 
serum  at  once  by  centrifugation.  The  custom  of 
arying  a  few  drops  of  blood  on  a  coverglass  or  on 
filter  paper,  and  of  sending  this  preparation  to  a 
laboratory  for  the  agglutination  reaction,  has  been 
practiced  quite  extensively,  and  is  a  justifiable 
procedure  when  it  is  not  possible  to  collect  the  pure 
serum.  It  has  the  disadvantage  that  the  experi- 
menter never  knows  exactly  how  much  blood  has 
been  collected,  and  consequently  can  not  perform 
the  test  with  exact  dilutions  of  the  serum,  the  im- 
portance of  which  will  be  pointed  out  below.  The 
red  corpuscles  and  debris  in  such  a  preparation  also 
interfere  with  the  clearness  of  the  field  in  micro- 
scopic examination,  a  difficulty  which  may  be 
partly  overcome  by  filtering  the  dissolved  serum. 
Serum  When  only  a  small  amount  of  serum  is  available, 
it  is  necessary  to  use  the  microscopic  method. 
Normal  human  serum,  when  concentrated,  and 
even  when  diluted  to  one  in  ten  or  higher,  some- 
times agglutinates  the  typhoid  bacillus  and  some 
other  organisms;  the  same  serum,  when  diluted  to 
one  in  forty  or  one  in  sixty,  may  not  agglutinate. 
The  serum  of  a  typhoid  patient,  however,  or  of  a 


Dilutions 


LOOP     MEASUREMENT.  215 

typhoid  convalescent  rarely  fails  to  agglutinate  in 
these  higher  dilutions.  It  is  generally  held  that 
a  dilution  of  one  in  forty  or  fifty  is  sufficiently 
high  to  eliminate  the  possibility  of  agglutination 
by  a  non-typhoid  serum,  and  sufficiently  low  to 
render  the  serums  of  all,  or  nearly  all,  typhoid  pa- 
tients agglutinating.  The  necessity  for  dilution  of 
the  serum  is  emphasized  by  the  additional  fact 
that  infections  with  related  organisms,  as  the  colon 
bacillus,  cause  a  slight  increase  in  the  agglutinat- 
ing power  for  the  typhoid  bacillus  along  with  a 
relatively  large  increase  of  colon  agglutinins.  A 
test  with  a  low  dilution  of  this  colon  serum  might 
give  a  positive  reaction  with  the  typhoid  bacillus 
and  lead  to  an  incorrect  interpretation;  but 
if  a  dilution  of  one  in  forty  were  used,  the  non- 
agglutination  of  the  typhoid  bacillus  would  speak 
against  a  typhoid  infection.  This  will  be  consid- 
ered under  "group  agglutination"  (Chapter  XIV). 

A    convenient    method    of    measuring    small  The  "Loop" 

-         - ,  T  .      ,  «  Measurement. 

amounts  of  culture  and  serum  is  by  means  of  a 
fine  platinum  wire  which  is  bent  at  its  tip  to  form 
an  eyelet  or  "loop."^  If  one  places  one  loop  of 
serum  into  a  small  watch  glass  or  hollow-ground 
slide,  and  adds  nine  logps  of  bouillon  or  of  salt 
solution,  a  dilution  of  one  in  ten  is  reached.  Five 
loops  of  this  mixture  with  five  of  the  diluent  gives 
a  dilution  of  one  in  twenty.  One  loop  of  the  sec- 
ond dilution,  to  which  is  added  one  of  the  culture 
suspension,  gives  the  desired  dilution  of  one  in 
forty.  The  last  may  be  mixed  directly  on  the 
coverglass,  and  then  inverted  on  a  hollow-ground 

3.  Pfeiffer  introduced  a  conventional  "loop"  of  such 
dimensions  that  it  holds  2  milligrams  of  bacterial  cells  as 
they  are  taken  from  a  solid  surface,  like  that  of  agar. 


216  INFECTION     AND     IMMUNITY. 

slide.     More  accurate  dilutions  can  be  made  by 
means  of  capillary  tubes. 

A  convenient  amount  of  serum  is  allowed  to 
enter  the  tube  by  capillary  attraction.  The  length 
of  this  column  is  marked  on  the  tube  and  then 
successive  volumes  of  the  diluent  drawn  in,  each 
being  separated  from  the  succeeding  one  by  a  small 
bubble  of  air.  It  is  readily  seen  how  with  even  a 
minute  quantity  of  serum,  one  may  make  the  test 
with  dilutions  of  one  in  ten,  one  in  twenty,  one  in 
thirty,  one  in  forty,  etc.,  details  which  are  neces- 
sary for  a  correctly  performed  test.  It  is  im- 
portant that  in  the  different  dilutions  the  same 
amount  of  bacterial  emulsion  be  used. 

In  the  macroscopic  test,  more  serum  is  neces- 
sar}^,  though  the  quantity  need  not  be  large,  and 
the  dilutions  are  made  in  test  tubes  of  suitable 
size.  One  should  always  deal  with  definite  quan- 
tities of  the  serum  dilutions,  and  should  always 
add  the  same  amount  of  bacterial  emulsion  in  the 
various  tubes  involved  in  a  test. 
The  Micro-  If  agglutination  occurs  in  the  microscopic  prep- 
Reaction,  aration  described  above,  one  sees,  with  the  high 
power,  in  the  course  of  from  fifteen  minutes  to  a 
half-hour,  that  two  or  more  micro-organisms 
which  come  in  contact  have  a  tendency  to  remain 
in  this  position.  In  the  case  of  a  motile  organism 
(typhoid)  the  movements  may  be  exaggerated  for 
a  time.  In  the  course  of  the  next  few  hours,  other 
cells  are  added  to  incipient  groups  and  new  groups 
originate.  Motility  becomes  less  and  less  and  event- 
ually ceases,  in  a  characteristic  reaction.  The 
maximum  change  has  taken  place  in  from  six  to 
eight  hours.    Not  less  than  four  or  five  cells  which 


AGGLUTININ     UNIT. 


217 


scopic 
Reaction. 


are  permanently  agglutinated  are  considered  in- 
dicative of  a  positive  reaction;  the  test  is  most 
decisive  when  large  masses  are  formed,  so  large  that 
they  are  seen  readily  with  a  low  magnification.  A 
similar  preparation  to  which  no  serum  has  been 
added  should  always  be  made,  in  order  to  eliminate 
spontaneous  or  "auto-agglutination"  as  a  possible 
source  of  error. 

In  a  macroscopic  test,  the  uniform  cloudiness  of  Tiie  Macm- 
the  mixture  of  serum  and  bacteria  becomes 
changed  by  the  formation  of  smaller  and  larger 
flakes  or  clumps  of  bacteria,  which  in  the  course  of 
a  few  hours  sink  to  the  bottom  as  a  white  precipi- 
tate, leaving  a  clear  overlying  fluid.  Here  also  a 
control  tube,  to  which  no  serum  has  been  added, 
should  be  preserved  for  comparison. 

The  body  temperature,  which  may  be  obtained 
in  a  thermostat,  facilitates  the  reaction. 

The  value  of  an  agglutinating  serum  can  not  be 
expressed  in  units  with  the  exactness  that  is  at- 
tained in  measuring  diphtheria  antitoxin  for  the 
following  reasons :  1,  The  limits  of  the  reaction  are 
not  sufficiently  definite ;  2,  a  given  mass  of  bacteria 
has  the  power  of  absorbing  varying  amounts  of 
the  agglutinating  substance,  depending  on  the  con- 
centration of  the  latter;  and  3,  it  is  impossible  to 
obtain  standard  bacterial  emulsions. 

One  may  arbitrarily  decide  on  a  unit  similar  to 
that  of  Zupnik,  in  which  a  serum  which  is  able 
to  agglutinate  a  given  mass  of  bacteria  in  a  dilu- 
•  tion  of  one  in  forty  is  taken  as  the  standard.  If  a 
similar  amount  of  a  serum  agglutinates  in  a  di- 
lution of  1  in  120  it  is  said  to  be  of  threefold 
strength. 


The     Aggluti- 
nin   Unit. 


218  INFECTION     AND     IMMUNITY. 

The  value  of  the  agglutination  reaction  as  a 
clinical  diagnostic  aid  will  be  considered  later  in 
connection  with  the  individual  diseases. 

Agrsriutination  A  Consideration  of  agglutination  would  be  in- 
**  Corpuscles,  complete  if  one  did  not  mention  the  phenomenon 
as  it  occurs  with  cells  other  than  those  of  bacteria, 
in  particular  the  red  blood  cells.  The  serums  of 
many  animals,  as  stated  in  a  previous  chapter,  are 
toxic  for  the  erythrocytes  of  some  other  species. 
In  some  instances,  the  corpuscles  lose  their  hemo- 
globin under  the  influence  of  the  serum  (hemoly- 
sis) ;  in  other  instances,  or  even  with  the  same 
serums  if  previously  heated,  the  corpuscles  are 
thrown  into  clumps  and  settle  to  the  bottom  of  the 
test  tube,  leaving  a  clear  overlying  fluid.  The 
analogy  with  the  bacterial  agglutinins  goes  still 
further,  in  view  of  the  fact  that  the  formation  of 
these  ^^lemagglutinins"  may  be  induced  artificially 
in  the  body  of  an  animal  by  the  injection  of 
erythrocytes  from  another  species.  An  animal 
does  not  form  agglutinins  for  its  own  cells  (auto- 
agglutinins),  but  often  does,  however,  for  the  cells 
of  another  member  of  the  same  species  (iso-agglu- 
tinins).  What  is  said  in  the  next  chapter  con- 
cerning the  specificity  of  the  bacterial  agglutinins 
also  holds  for  the  hemagglutinins. 

Plant  Hemag.  Certain  plant  toxins,  true  toxins  with  hapto- 
phorous  and  toxophorous  structures,  agglutinate 
red  blood  cells:  ricin,  abrin,  crotin,  etc.  Some  of 
the  earliest  and  most  important  work  which 
Ehrlich  has  done  in  the  field  of  immunity  was  ac- 
complished with  these  plant  toxins. 


grlntinins. 


CHAPTEE    XIV 


THE  NATURE   OF   THE    SUBSTANCES    CONCERNED   IN 
AGGLUTINATION. 

Two  substances  are  concerned  in  agglutination :  Terms. 
one^  the  active  or  agglutinating  substance,  exists 
in  the  serum,  while  the  other,  the  substance  acted 
on  or  the  agglutinable  substance,  is  present  in  the 
bacteria.  The  agglutinable  substance  is  generally 
supposed  to  be  passive  in  the  reaction,  while  the 
agglutinating  property  seems  to  possess  a  ferment- 
like  element,  which  acts  on  the  agglutinable  sub- 
stance. Agglutinin,  the  term  used  in  the  preced- 
ing chapter,  is  now  generally  applied  to  the  sub- 
stance in  the  serum.  Eecently  the  bacterial  con- 
stituent has  been  called  agglutinogen,  because  of 
the  belief  that  the  agglutinable  substance,  when 
introduced  into  the  animal  body,  stimulates  the 
latter  to  the  formation  of  agglutinin;  hence  ag- 
glutinogen means,  not  agglutination-producing, 
but  agglutinin-producing.  These  shorter  terms 
will  be  used  for  the  sake  of  convenience. 

The  presence  of  agglutinogen  in  an  organism  As-siutinogen. 
may  be  demonstrated  in  three  ways :  1.  The  mere 
fact  of  its  agglutinability  by  a  serum  is  evidence 
of  the  presence  of  an  agglutinable  substance.  2. 
If  during  infection  or  immunization  the  serum  ac- 
quires agglutinating  properties,  the  bacterium  pos- 
sesses an  aggiutinogenic  substance.  3.  If  a  cul- 
ture is  mixed  with  a  serum  containing  the  specific 
agglutinin,  and  after  a  period  of  contact  is  re- 
moved by  centrifugation,  the  resultant  disappear- 


220  INFECTION     AND     IMMUNITY. 

ance  of  agglutinin  from  the  serum,  which  may  be 
demonstrated,  shows  that  something  in  the  bac- 
teria (agglutinogen)  has  combined  with  the  ag- 
glutinin. 

Distribution  The  locatiou  of  agglutinogen  in  the  bacterial 
nogen.  cclls  has  reccived  some  discussion.  There  is  a  tend- 
ency to  believe  that  it  exists  in  the  cell  envelope  or 
perhaps  on  its  surface.  It  appears  to  be  formed  in 
the  cell,  and,  in  some  cases,  it  may  be  excreted  into 
a  surrounding  medium;  certainly  when  bacteria 
die  and  disintegrate  agglutinogen  is  liberated.  The 
filtrates  of  certain  cultures  (entirely  free  from 
bacterial  cells),  when  injected  into  animals,  will 
cause  the  formation  of  agglutinins.  Also,  just  as 
a  micro-organism  is  able  to  absorb  agglutinin  from 
the  corresponding  antiserum  by  a  process  of 
chemical  union,  so  a  filtrate  of  the  type  mentioned 
is  able  to  neutralize  the  agglutinating  power  of  the 
serum.  In  these  instances,  agglutinogen  becomes 
free  as  a  consequence  of  disintegration  of  some  of 
the  bacterial  cells. 

The  Precipi-  The  filtratcs  of  Certain  cultures  exhibit  another 
Reaction  phenomenon  when  they  are  mixed  with  their  spe- 
cific antiserums;  this  has  to  do  with  the  bacterial 
precipitins  of  Kraus.  If,  for  example,  the  filtrate 
of  an  old  typhoid  bouillon  culture  is  mixed  with 
antityphoid  serum,  a  distinct  precipitate  is  formed 
which  eventually  settles  to  the  bottom  of  the  tube. 
This  is  a  specific  reaction,  and  does  not  occur  if  the 
filtrate  is  mixed  with  some  other  immune  serum. 
It  is  thought  by  some  that  this  so-called  precipi- 
table  substance  in  the  filtrate  is  identical  with  the 
aggiutinable  substance  (agglutinogen),  but  this 
point  is  still  the  subject  of  investigation. 


AGGLUTINOGEN. 


221 


Multiplicity 
of    Agrslntino- 
g'ens. 


Agglutinogen  may  be  extracted  from  micro- 
organisms by  chemical  processes.  The  presence 
of  the  substance  in  the  extracts  becomes  manifest 
when  immunization  with  them  causes  the  forma- 
tion of  an  agglutinating  serum.  This,  again,  is 
the  "test  of  immunization.^^ 

The  agglutinogen  of  one  bacterium  is  not  iden- 
tical with  that  of  any  other.  If  they  were  identi- 
cal, immunization  with  the  one  would  yield  an  ag- 
glutinating serum  of  equal  power  for  both  cells; 
this,  however,  is  not  the  result  obtained.  On  the 
other  hand,  the  agglutinins  of  two  different  organ- 
isms may  coincide  to  a  certain  degree,  as  will  be 
shown  under  the  subject  of  "group  agglutination." 
Certain  experiments  go  to  show  that  the  agglutin- 
ogen of  even  a  single  micro-organism  is  not  uni- 
form substance.  One  portion  is  heat-susceptible, 
being  destroyed  at  62  C,  while  another  portion  is 
said  to  resist  a  temperature  of  165  C.  Such  tech- 
nical questions  continue  to  be  investigated. 

Agglutinogens  are  said  to  pass  through  semi- 
permeable membranes,  while  agglutinins  do  not. 

Smith  and  Eeagh  distinguish  two  kinds  of  ag- 
glutinogen in  those  bacteria  which  possess  flagella, 
one  peculiar  to  the  cell  body,  and  the  other  to  the 
flagellse. 

x\gglutinin  may  be  precipitated  completely  from  P>*op«^*i^f:  *** 
a  serum  by  the  sulphates  of  magnesium  or  ammo- 
nium, when  the  salts  are  used  in  proper  concentra- 
tions. Because  of  their  reaction  to  such  precipi- 
tating agents,  agglutinins,  are  thought  to  belong  to 
the  globulin  fraction  of  serums ;  whether  globulins 
or  not,  they  are  precipitated  with  them. 

Agglutinins  resist  digestion  with  pepsin  and 
papayotin,  but  are  destroyed  after  prolonged  ex- 


Flasellar    and 
Somatic    Ag- 
Slutinogens. 


Asglutinins. 


222  INFECTION     AND     IMMUNITY. 

posure  to  the  action  of  trypsin.  An  agglutinating 
serum  which  is  dried  and  kept  free  from  moisture 
and  the  action  of  light  retains  its  power  unaltered. 
Similar  to  agglutinogen,  agglutinin  is  thought  not 
to  be  a  uniform  substance,  one  portion  being  sus- 
ceptible to  heat,  and  another  portion  resistant; 
these  have  been  called  alpha  and  beta  agglutinins. 

strnctnre  of  It  is  Convenient  to  speak  of  the  reaction  between 
agglutinin  and  agglutinogen,  and  of  the  process  m 
the  body  through  which  agglutinins  are  formed,  in 
terms  of  the  side-chain  theory.  Accordingly,  if 
that  constituent  of  micro-organisms  which  we  have 
termed  agglutinogen  is  the  substance  which  stimu- 
lates the  tissues  to  form  agglutinin,  we  must  as- 
sign to  it  a  haptophorous  group  through  which  it 
may  unite  with  the  receptors  of  the  tissue  cells. 
This  haptophore  comes  into  play  again  in  the  union 
between  agglutinogen  and  agglutinin,  which  pre- 
cedes agglutination.  There  is  no  reason  for  as- 
signing to  agglutinogen  any  other  structure  than 
this  single  haptophore;  it  is  a  passive  body,  similar 
to  antitoxin,  and  has  no  other  function  than  that 
of  uniting  either  with  cell  or  with  agglutinin. 

strncture  of  Agglutinin  also  must  have  a  haptophorous  or 
Aegintiniii.  ]3Jjj(jjjjg  group,  iuasmucli  as  it  enters  into  combina- 
tion with  agglutinogen.  In  addition  to  this  bind- 
ing group,  experiments  have  shown  that  agglutinin 
possesses  a  toxic  constituent,  which  is  analogous 
to  the  toxophorous  group  of  the  toxin  molecule. 
In  this  case,  however,  it  is  called  a  zymotoxic, 
zymotoxic  zvmophorous  or  agglutinophorous  group;  suppos- 
Gronp.  g(j|y  j^  j^^g  a  ferment-like  activity  (Fig.  6).  The 
analogy  with  toxins  goes  further,  in  that  the 
zymotoxic  group  of  agglutinin  may  degenerate  or 
may  be  destroyed,  leaving  the  haptophorous  group 


AGGLUTINOIDS. 


223 


with  its  binding  power  for  agglutinogen  practi-  Assintinoids, 
cally  unaltered;  these  are  agglutinoids,  just  as 
toxins  when  changed  in  a  similar  way  are  called 
toxoids.  A  serum  which  is  rich  in  agglutinin  may 
be  changed  into  one  rich  in  agglutinoid  by  expo- 
sure to  a  temperature  of  from  60  to  75  C,  and  by 
the  action  of  acids  or  alkalies;  the  change  also 
takes  place  spontaneously  in  the  course  of  time, 
when  the  agglutinin  is  in  solution. 

Agglutinoids  are  detected  by  methods  analogous 
to  those  used  in  the  recognition  of  toxoids.  If 
toxoids  unite  with  all  the  antitoxin  in  a  solution, 
there  naturally  remains  no  antitoxin  to  unite  with 
true  toxin  which  may  be  added  subsequently.  Sim- 
ilarly, if  all  the  agglutinogen  in  a  mass  of  micro- 
organisms has  united  with  inactive  agglutinoid, 
agglutinin  which  is  added  subsequently  would  have 
no  point  of  attack  and  the  reaction  of  agglutina- 
tion would  not  occur.  So  we  may  say  that  when 
bacteria  are  treated  with  a  serum  which  has  lost 
its  original  agglutinating  power,  and  the  bacteria 
are  there])y  made  insusceptible  to  the  action  of  a 
fresh  agglutinating  serum,  the  former  serum  con- 
tains agglutinoids. 

Sometimes  it  is  found  that  even  a  fresh  serum, 
when  concentrated,  will  cause  less  agglutination 
than  when  diluted.  This  has  been  referred  to  the 
presence  of  agglutinoids  which  have  a  stronger 
affinity  for  agglutinogen  than  has  the  agglutinin; 
when  of  this  character  they  are  called  proagglu- 
tinoids,  and  accordingly  are  analogous  to  the  pro- 
toxoids  mentioned  earlier.  As  the  serum  is  diluted 
the  concentration  of  the  pro-agglutinoids  becomes 
less,  and  at  a  time  when  they  are  so  dilute  that  they 
have  no  influence  on  the  reaction,  the  agglutinins 


Proas- 
^lutinoids. 


224  INFECTION     AXD     IMMUNITY. 

are  still  present  in  such  quantity  that  agglutina- 
tion is  brought  about. 
Two  stagres  in  The  ppcsence  of  some  salt  is  necessary  for  the 
tion.  occurrence  of  agglutination.  Bordet  found  that 
if  the  salts  were  removed  from  the  serum  and  from 
the  suspension  of  bacteria  by  dialysis,  and  the  two 
were  then  mixed,  agglutination  did  not  occur;  if 
a  small  trace  of  sodium  chlorid  was  added  the  re- 
action took  place  promptly.  Furthermore,  if  the 
serum  was  completely  removed  from  the  bacteria 
by  repeatedly  washing  them  in  distilled  water,  it 
was  found  that  the  microbes  had  absorbed  the  ag- 
glutinin, but  the  latter  remained  inactive  until  the 
salt  was  added. 

This  experiment  not  only  suggests  a  haptophor- 
ous  as  distinguished  from  a  z3nnotoxic  group,  but 
also  indicates  that  agglutination  consists  of  two 
phases.  The  first  phase  represents  the  union  of 
agglutinin  with  the  bacteria,  while  in  the  second 
are  included  the  other  changes  necessary  for  the 
clumping  of  the  organisms,  in  which  the  activity 
of  the  zymotoxic  group  is  represented.  The  action 
of  the  salt,  just  cited,  is  unknown. 

The  properties  of  serums  which  are  of  interest 
in  immunity  are  now  being  studied  by  chemists, 
notably  by  Arrhenius.  The  study  of  mass  action, 
of  chemical  equilibrium  between  agglutinin  and 
agglutinogen,  for  example,  and  of  the  dissociation 
of  the  compound  after  it  has  once  formed,  are 
subjects  under  investigation,  but  which  are  too 
technical  to  be  entered  od  here. 
Gronp  Ag-  "Group  agglutination"  has  been  referred  to.  By 
this  is  meant  the  ability  of  an  antimicrobic  serum 
to  agglutinate  certain  other  organisms  which  mor- 
phologically,  biologically   and   often   pathogeneti- 


GROUP     AGGLUTINATION'.  225 

caily,  are  closel}^  related  to  the  homologous  bac- 
terium. In  these  instances,  the  agglutinating 
power  is  greatest  for  the  homologous  organism, 
and  the  degree  to  which  the  heterologous  organisms 
are  agglutinated  is,  to  some  extent,  an  index  of 
the  proximity  of  the  relationship  of  the  latter  to 
the  former.  Antityphoid  serum  has  been  found  to 
agglutinate  the  psittacosis,  colon,  paracolon,  and 
paratyphoid  bacilli  and  Bacillus  enteritidis,  but 
the  action  is  never  so  strong  as  on  the  typhoid 
bacillus  itself.  We  are  to  understand  that  this 
power  to  agglutinate  related  organisms  represents 
something  more  than  the  normal  property  of  the 
serum;  there  has  been  an  actual  increase  in  agglu- 
tinin for  the  heterologous  bacteria  as  a  result  of 
infection  or  immunization  by  the  primary  organ- 
ism. 

Having  typhoid  fever  in  mind,  this  is  a  rule 
which  works  both  ways.  Infections  with  the  colon 
bacillus  and  related  organisms,  and  sometimes 
with  organisms  not  closely  related,  as  the  staph3do- 
coccus,  may  cause  an  increase  in  agglutinin  for  the 
typhoid  bacillus.  The  importance  of  this  fact  is 
evident,  and  it  may  explain  the  positive  Gruber- 
Widal  reaction  sometimes  found  in  infections 
other  than  typhoid. 

Inasmuch  as  the  highest  agglutinating  power  is  ciiief  Aprsrin- 
always  manifest  against  the  homologous  organism,  A^siiotrnin.**' 
this  is  spoken  of  as  the  chief  agglutinin  (Haupt- 
agglutinin)  of  the  serum,  while  the  weaker  agglu- 
tinins for  other  organisms  are  called  partial  or  ad- 
ventitious agglutinins,  or  coagglutinins  (Mitag- 
glutinm) . 

The  phenomenon  of  group  agglutination  would   specificity. 
seem  to  violate  the  specificity  which  we  are  in  the 


226  INFECTION     AND     IMMUNITY. 

habit  of  attributing  to  the  reactions  of  immunity; 
yet  a  reasonable  explanation  has  been  offered  for 
the  occurrence.  It  is  probable  that  the  proto- 
plasms of  all  cells  have  certain  constituents  in 
common,  and  that  the  closer  the  relationship  be- 
tween two  different  cells  the  greater  is  the  simi- 
larity of  their  constituents.  In  view  of  this  prob- 
abilit}^,  Durham  has  used  the  following  illustra- 
tion in  the  explanation  of  group  agglutinations : 
The  typhoid  bacillus  contains  certain  constituents, 
agglutinogenic  molecules,  which  one  may  desig- 
nate as  a,  b,  c,  d,  and  e;  these  differ  among  them- 
selves in  unknown  respects,  but  each  is  able  to 
stimulate  to  the  formation  of  a  corresponding  ag- 
glutinin. The  serum,  then,  would  have  the  ag- 
glutinin molecules  A,  B,  C,  D  and  E,  also  differing 
among  themselves,  but  having  at  least  one  property 
in  common — that  of  causing  agglutination  of  the 
typhoid  bacillus  by  uniting  with  the  correspond- 
ing agglutinogenic  molecules.  In  this  sense  noth- 
ing could  be  more  specific.  The  Bacillus  enteri- 
tidis,  closely  related  to  the  typhoid  organism,  may 
possess  the  agglutinogenic  molecules  c,  d,  e,  f,  g, 
and  h,  and  following  the  principle  expressed  above 
would  stimulate,  in  the  body,  to  the  formation  of 
the  agglutinin  molecules  C,  D,  E,  F,  G  and  H. 
Inasmuch  as  the  agglutinogens  c,  d  and  e  are  com- 
mon to  the  two  bacilli,  the  agglutinins  C,  D  and  E, 
which  are  present  in  both  serums,  would  affect 
pi'ther  of  the  two  organisms.  The  typhoid  serum, 
however,  would  contain  five  agglutinins  for  the 
typhoid  bacillus  and  only  three  for  the  Bacillus 
enteritidis ,  consequently  the  action  would  be 
stronger  against  the  typhoid  bacillus;  mutato  mu' 
inndis,  the  samf^  applies  to  the  entoritidis  sornm 


SPECIFICITY     OF    SERUM. 


227 


Importance  of 
Serum 


The  same  line  of  reasoning  would  explain  the  in- 
creased agglutinating  power  of  an  anticolon  serum 
for  the  typhoid  bacillus. 

A  further  elaboration  of  this  principle  may  be 
made  in  a  case  in  which  two  different  strains  of 
the  same  organism  (typhoid  bacillus)  have  some- 
what different  agglutinogenic  molecules;  conse- 
quently the  homologous  immune  serums  for  the 
two  organisms  might  not  coincide  in  their  ag- 
glutinating powers  for  a  third  strain  of  the  bacil- 
lus. 

In  view  of  the  points  mentioned,  it  is  clear  that 
specificity  of  a  given  serum  may  be  determined 
only  by  diluting  the  sernm  to  such  an  extent  that 
the  coagglutinins  practically  are  eliminated,  the 
chief  agglutinin  being  present  in  so  much  greater 
concentration  that  it  is  still  able  to  agglutinate 
the  homologous  bacterium. 

Theoretically,  it  is  also  important  for  the  spe- 
cificity of  the  reaction  that  the  particular  strain 
of  the  organism  to  be  used  for  the  test  correspond 
in  its  agglutinogenic  molecules  or  receptors  with 
those  of  the  strain  used  for  the  immunization ;  the 
agglutinogenic  receptors  should  be  typical  for  the 
organism. 

It  is  doubtful  if  group  agglutination  occurs 
among  all  closely  related  bacteria,  inasmuch  as 
Kolle  found  that  it  did  not  exist  among  the  vib- 
rios. 

It  is  thought  possible  that  the  multiple  agglu-  Dilutions. 
tinating  power  of  a  serum  may  be  caused  by  mixed  infections. 
infections  in  some  instances.     Although  this  is  to 
be  kept  in  mind,  one  should  not  overestimate  its 
diagnostic   importance,   because   a   similar  multi- 


228  INFECTION     AND     IMMUNITY.  ^^ ' 

piicitj  may  result  from  infection  b}^  a  single  miero- 
organism. 
Production       The  explanation  of  the  production  of  aggluti- 
tinins.  nius  b}^  the  bod}^,  according  to  the  conception  of 
TheoW.  Eirrlich,  is  similar  to  that  already  given  for  the 
production  of  antitoxins.    That  is  to  say,  the  ag- 
glutinin molecules  are  cast-off  cell  receptors,  the 
overproduction  of  which  has  occurred  as  a  result  of 
their  union  with  the  agglutinogenic  molecules  of 
the  bacteria.     The  antitoxin  receptors  were  rela- 
tively simple,  having  no  other  demonstrable  struc- 
ture than  that  of  the  haptophorous  groups  through 
which  they  unite  with  the  corresponding  toxin. 
Receptors  of  \Yg  j^avc  recosTnizcd  in  the  ao^srlutinin  receptor  two 

Second  o  oo  r 

Order,  gpoups,  a  haptopliorous  and  a  zymotoxic;  conse- 
quently it  must  have  this  same  structure  when  it 
is  still  a  part  of  the  cell.  Ehrlich  designates  it  as 
a  receptor  of  the  second  order,  which,  being  de- 
fined, is  a  receptor  in  which  a  haptophorous  and  a 
zymotoxic  group  exist  as  integral  parts  of  the 
molecule  (Fig.  6). 

In  accordance  with  the  side-chain  theory,  the 
ability  of  an  animal  to  form  agglutinins  for  a  cer- 
tain organism  would  depend  on  its  possession  of  re- 
ceptors of  the  second  order  which  are  able  to  unite 
witli  the  agglutinogenic  receptors  of  the  bacterium. 
It  is  well  established  that  different  animals  may 
not  form  serums  with  equal  agglutinating  powers 
for  an  organism.  The  following  is  a  concrete  ex- 
ample: Wassermann  immunized  rabbits,  guinea- 
pigs  and  pigeons  with  a  strain  of  the  colon  bacil- 
lus, and  tested  the  three  scrums  with  fifteen  other 
strains  of  the  same  organism.  The  serum  of  the 
guinea-pigs  readily  agglutinated  the  strain  which 
was  used  for  immunization,  but  scarcelv  affected 


SPECIFICITY     OF     SERUM. 


229 


the  others.  Tlie  serums  of  the  rabbits  and  pigeons 
also  agglutinated  the  homologous  culture,  but  the 
coagglutinins  which  they  possessed  did  not  affect 
other  strains  equally.  Consequently,  it  was  sup- 
posed that  the  cells  of  the  three  animals  contained 
a  limited  number  of  receptors  in  common,  whereas 


Fig.  6. — Graphic  representation  of  receptors  of  the  second 
order  and  of  some  substance  uniting  with  one  of  them,  c, 
cell  receptor  of  the  second  order  ;  d,  toxophore  or  zymophor- 
ous  group  of  the  receptor  ;  e,  haptophore  of  the  receptor  ;  f, 
food  substance  or  product  of  bacterial  disintegration  uniting 
with  the  haptophore  of  the  ceU  receptor.  From  Ehrlich's 
"Schlussbetrachtungen,"  Nothnagel's  System  of  Medicine, 
vol,  viii. 

other  receptors  which  were  present  in  one  of  the 
animals  were  largely  wanting  in  the  other  two. 

Inagglutinability  was  mentioned  as  a  charac- 
teristic of  certain  bacteria,  especially  the  bacillus 
of  Friedlander.  This  condition  is  much  more 
important   when   it   involves    an   organism   which 


Agglntinabil- 
ity  of  Some 
Organism-s. 


230  INFECTION     AND     IMMUNITY. 

iisuaily  is  acf^lntinated  with  ease.  In  some  in- 
stances, the  tjq^hoid  bacillus  when  freshly  culti- 
vated from  a  patient,  or,  indeed,  from  contami- 
nated water,  has  been  found  to  resist  agglutination 
by  a  strong  serum;  the  same  organism  after  a 
period  of  existence  on  artificial  media  becomes  ag- 
glutinable.  Widal  and  Sicard  noted  that  often  the 
serum  of  a  typhoid  patient  would  not  agglutinate 
the  bacillus  which  had  been  cultivated  from  the 
patient's  own  body,  although  the  same  serum 
would  agglutinate  laboratory  cultures.  Cultiva- 
tion of  the  typhoid  bacillus  at  42  C.  will  cause  it 
to  lose  its  agglutinable  property,  but  it  may  be  re- 
established by  subsequent  cultivation  at  lower 
temperatures.  It  seems  that  this  variation  must 
be  due  to  some  change  in  the  bacteria,  i.  e.,  in  the 
agglutinable  substance.  It  is  possible  that  the 
organism,  during  its  existence  in  the  animal,  be- 
comes immunized  against  the  action  of  the  agglu- 
tinin just  as  the  animal  becomes  immunized 
against  the  toxic  action  of  bacteria.  This  condi- 
tion in  the  micro-organisms  would  then  be  repre- 
sented by  a  great  excess  of  agglutinogenic  recep- 
tors, so  that  a  much  greater  amount  of  agglutinin 
would  be  required  to  cause  clumping.  It  is  read- 
ily seen  how  the  use  of  an  inagglutinable  strain  of 
the  typhoid  bacillus  would  affect  serum  diagnosis. 
Theories  of  We  are  to  consider  that  in  the  phenomenon  of 
tion.  agglutination  a  reaction  of  a  chemical  or  physico-' 
chemical  nature  takes  place  between  the  agglutinin 
of  the  serum  and  the  agglutinogen  of  the  micro- 
organisms, the  actual  clumping  following  as  a 
consequence  of  this  reaction.  It  is  not  a  "yitsl" 
reaction,  for  dead  bacteria  may  be  agglutinated. 


AGGLUTINATION.  231 

Theories  of  agglutination  have  to  do,  not  with 
the  existence  of  agglutinin  and  agglutinogen,  but 
rather  with  the  nature  of  the  reaction  between  the 
two,  and  the  influences  which  bring  about  the 
clumping  after  the  reaction  has  occurred.  The 
original  theory  of  Gruber  supposed  that  the  serum 
so  afi:'ected  the  bacteria  that  they  became  sticky; 
consequently,  as  they  came  in  contact,  they  were, 
so  to  say,  glued  together.  Dineur  thought  changes 
occurred  in  the  flagellae  of  the  organisms,  a  theory 
which  is  untenable  because  some  bacteria  are  ag- 
glutinable  which  do  not  possess  flagellae.  Em- 
merich and  Loew  refer  agglutination  to  the  action 
of  an  enzyme  which  is  produced  by  the  bacterium 
itself,  a  theory  which  is  not  given  general  credence. 
Bordet  excludes  the  vitality  or  motility  of  the  or- 
ganisms as  factors,  and  believes  that  the  process  is 
purely  a  physical  one,  because  of  the  fact  that 
some  laiown  chemical  substances  may  be  made  to 
precipitate  or  to  agglutinate  certain  other  sub- 
stances (precipitation  of  colloids  by  salts)  ;  the 
theory  presupposes  some  change  in  the  molecular 
attraction  between  the  microbes  and  the  surround- 
ing fluid. 

Other  theories  have  to  do  with  the  question  of 
precipitation.  As  previously  stated,  when  the  fil- 
trates of  cultures  of  certain  organisms  are  mixed 
with  their  corresponding  immune  serums,  precipi- 
tates occur  in  the  mixtures.  It  was  mentioned 
that  the  substance  in  the  filtrate  which  takes  part 
in  the  precipitation  may  represent,  in  part,  the  ag- 
glutinable  substance  which  has  been  excreted  by 
the  bacteria.  McoUe  supposes  that  the  agglutin- 
able  substance  resides  in  the  external  layer  of  the 
bacteria  and  that  when  the  serum  is  added  a  coag- 


232  INFECTION     AND     IMMUNITY. 

ulation  occurs  in  the  envelope,  rendering  coales- 
cence with  the  envelopes  of  other  individuals  pos- 
sible. The  theory  of  Paltauf  that  the  agglutinable 
substance  finds  its  way  to  the  surface  of  the  bac- 
terium and  is  precipitated  by  its  union  with  ag- 
glutinin is  somewhat  similar.  The  shell  of  the  co- 
agulated substance  accounts  for  the  sticky  charac- 
ter which  the  envelope  acquires,  according  to  the 
theory  of  Gruber.  Paltauf  cites  observations 
which  tend  to  show  that  some  substance  actually 
is  extruded  from  the  micro-organisms  during  ag- 
glutination, and  that  in  properly  stained  speci- 
mens it  can  be  seen  as  a  precipitate  surrounding 
and  between  adjacent  organisms. 

The  multiplicity  of  theories  leads  one  to  suspect 
that  the  true  nature  of  the  process  remains  obscure. 
The  physical  nature  of  the  reaction  is  strongly 
supported  by  the  facts  that  bacteria  may  also  be 
agglutinated  and  precipitated  by  well-known  chem- 
ical substances,  such  as  hydrochloric  acid,  and  by 
various  organic  and  inorganic  colloids  (colloidal 
solutions  of  calcium  chlorid  (CaCU),  zinc  sulphate 
(ZuSo^),  ferric  hydroxid  (Fe(OH),),  aluminum 
hydroxid  (A1(0H)3),  ferric  chlorid"  (FeCI,,)  and 
aluminum  chlorid  (AICI3).  Some  of  these  sub- 
stances behave  like  the  agglutinating  serums  in 
the  possession  of  the  so-called  prozone;  i.  e.,  they 
may  fail  to  agglutinate  in  more  concentrated  solu- 
tions, whereas  after  dilution,  their  agglutinating 
power  becomes  manifest  (hydrochloric  acid  and  the 
staphylococcus,  according  to  Buxton  and  Rahe). 
Still  further  indirect  evidence  of  this  nature  of 
the  reaction  is  found  in  the  observation,  made  first 
by  Neisser  and  Friedberger,  that  two  colloids  which 


AGGLUTINATION.  233 

bear  opposite  electrical  charges  result  in  sedimenta- 
tion when  they  are  mixed  in  suitable  proportions. 
Eosin  and  Bismarck  brown,  mastic  and  colloidal 
ferric  hydroxid  (Fe(0H)3),  colloidal  silicic  acid 
and  colloidal  ferric  hydroxid  are  mixtures  which 
behave  in  this  way.  Here  also  the  inhibiting 
"prozone"  is  obtained  in  concentrated  solutions. 

An  analogy  appears  to  exist  between  bacteria 
which  have  absorbed  agglutinin  and  certain  colloids 
in  that  both  may  be  agglutinated  by  the  addition 
of  suitable  electrolytes.  This  phase  of  the  agglu- 
tination of  bacteria  was  referred  to  previously.  In 
a  like  manner  "agglutinin-bacteria"  and  the  col- 
loids mentioned  may  alike  be  precipitated  by 
various  salts  (electroh'tes),  such  as  the  chlorids  of 
sodium,  calcium  and  potassium,  and  many  others.^ 

1.  Buxton  and  Rahe  :  Jour.  Med.  Research,  1909,  xs,  113. 


CHAPTER    XV. 


Precipitins. 


PRECIPITINS. 

Because  of  their  scientific  importance  and  cer- 
tain practical  features,  the  serum-precipitins 
should  receive  something  more  than  the  incidental 
mention  which  has  been  given  them  under  agglu- 
tination and  in  other  chapters. 
Bacterial  In  1897  Kraus  discovered  that  bouillon  cultures 
of  the  organisms  of  typhoid,  cholera  and  plague, 
from  which  the  bacteria  had  been  removed  by  fil- 
tration, would  cause  precipitates  when  mixed  with 
their  respective  antiserums.  The  reaction  is  spe- 
cific. As  stated  later,  however,  this  specificity 
holds  only  when  those  quantitative  relationships 
are  observed  which  were  found  so  essential  for  the 
agglutination  test.  The  precipitins  of  Kraus  are 
the  bacterial  precipitins.  He  proposed  their  use 
for  the  identification  of  micro-organisms.  If,  for 
example,  one  has  in  hand  a  culture  which  he  sus- 
pects to  be  that  of  the  typhoid  bacillus,  it  may  be 
grown  in  a  liquid  medium,  the  cells  removed  by 
filtration,  and  the  filtrate  mixed  with  a  known 
antityphoid  serum;  if  a  precipitate  occurs  when 
the  serum  is  sufficiently  diluted,  the  reaction  indi- 
cates that  the  organism  in  question  is  the  typhoid 
bacillus.  Inasmuch  as  precipitins  are  formed  dur- 
ing the  course  of  some  infections  it  may  be  possible 
to  use  them  in  clinical  diagnosis,  but  for  either 
bacterial  or  clinical  diagnosis  the  agglutination 
test  is  more  readily  performed  and  interpreted. 


PRECIPITINS. 


235 


Phytoprecipitins  are  produced  by  immuniza- 
tion with  albuminous  substances  of  plant  origin, 
as  ricin  and  albumin  from  grains,  and  their  action 
is  specific  for  the  homologous  substance. 

Zooprecipitins  are  obtained  by  immunizing  with 
animal  albumins.  Through  the  work  of  Wasser- 
mann  and  Uhlenhuth,  of  Nuttall,  and  others,  it 
has  been  demonstrated  as  a  general  law  that  im- 
munization with  an  albumin  from  whatsoever 
source  gives  rise  to  the  formation  of  a  precipitin 
which  manifests  its  action  only  against  the  par- 
ticular albumin  used  for  the  immunization.  Hence, 
the  albumin  of  a  particular  serum,  in  some  un- 
kno^vn  respect,  is  different  from  that  of  all  others ; 
it  is  special  to  the  species. 

Immunization  with  milk  causes  the  formation 
of  a  precipitin  which  throws  down  the  casein  of 
the  milk  used  for  injection,  but  not  that  of  milk 
from  another  species.  The  milk  of  the  goat  may 
be  differentiated  from  that  of  the  cow  by  the  use 
of  the  lactoserum. 

Likewise,  after  the  injection  of  egg-white  a 
precipitin  is  formed  which  is  specific  for  the  type 
injected. 

Three  substances  are  open  to  study  in  the  pre- 
cipitation reaction.  First,  the  fluid  or  substance 
which  is  used  for  immumzation ;  it  bears  the  name 
of  precipitogen,  i.  e.,  the  precipitin-producing  sub- 
stance. Second,  the  specific  constituent  of  the 
precipitating  serum,  i.  e.,  the  precipitin.  Third, 
the  precipitate,  which  is  a  consequence  of  the  reac- 
tion between  precipitogen  and  precipitin.  We  are 
able  to  recognize  in  this  instance  the  actual  end- 
product  of  a  reaction,  a  condition  which  is  not  so 
easily  realized  in  other  ^^immunity  reactions."    It 


Pliytoprecipi- 
tinn    and 
Zooprecip- 
itins. 


Lactosernm. 


Precipitogen, 
Precipitin 
and  Precipi- 
tate. 


236  INFECTION     AND     IMMUNITY. 

is  true,  of  course,  that  little  lias  been  learned  con- 
cerning the  nature  of  the  end-product ;  its  chemis- 
try is  as  dark  as  that  of  the  proteids  in  general. 
Formation  of  As  statcd  in  the  chapter  on  "Natural  Immun- 
recipi  111.  ^^^„  normal  serums  occasionally  have  the  power 
to  cause  precipitates  in  other  serums.  Precipitins 
for  egg  albumin  and  goat  serum  have  been  found 
in  extracts  of  organs,  although  at  the  same  time 
they  were  absent  from  the  serum  of  the  animal. 
In  this  case  the  active  bodies  exist  in  the  cells  as 
"sessile  receptors,"  and  by  the  process  of  extraction 
they  are  brought  into  solution.  During  immuniza- 
tion these  same  receptors  are  stimulated  to  over- 
production and  are  throi^m  into  the  circulation  as 
free  precipitin  receptors. 

Tlie  power  of  forming  precipitins  may  be  widely 
distributed  among  the  organs.  This  function  has 
been  assigned  to  the  leucocytes  (Kraus  and  Leva- 
diti,  Moll),  and  in  one  case  they  were  formed 
locally  in  the  anterior  chamber  of  the  eye  (v. 
Dungern,  Eomer). 

For  the  artificial  production  of  precipitins  the 
precipitinogenous  fluid  may  be  injected  into  the 
veins,  peritoneal  cavity  or  the  subcutaneous  tissue. 
Within  from  four  and  a  half  to  five  days  the  pre- 
cipitin has  been  formed  to  such  an  extent  that  it 
may  be  demonstrated  in  the  serum  of  the  im- 
munized animal. 
coiioorninar  As  in  the  case  of  agglutinin  formation,  not  all 
tin«**aVni*iioI  auimals  have  equally  the  power  of  forming  a  pre- 
cipitin for  a  given  albumin.  This  point,  as  re- 
lated to  serum  precipitins,  is  of  particular  impor- 
tance, and  involves  a  factor  which  is  of  no  conse- 
quence in  bacterial  agglutinins.  In  the  first 
place,  an  animal  will  not  form  a  precipitin  whicli 


preeipiliiiN. 


FRECIPITINS.  237 

is  active  against  its  own  serum,  i.  e.,  by  bleeding 
an  animal  and  reinjecting  the  serum  a  specific  pre- 
cipitin is  not  formed.  If  formed  it  would  be  an 
autoprecipitin,  and,  as  a  rule,  animals  do  not  form 
antibodies  for  their  own  tissue  constituents. 
Again,  animals  are  less  likel}^  to  form  antibodies 
for  the  tissue  constituents  of  other  members  of  the 
same  species  than  for  those  of  other  species ;  these, 
when  formed,  are  called  iso-antibodies.  Schutze 
immunized  thirty- two  rabbits  with  serum  from  the 
rabbit  and  obtained  an  iso-precipitin  from  only  two 
of  the  number.  In  the  third  place,  animals  do  not 
readily  form  anti-bodies  for  the  tissue  constituents 
of  other  animals  which  zoologically  or  biologically 
are  closely  related.  Immunization  of  the  guinea- 
pig  with  the  serum  of  the  rabbit,  a  pigeon  with 
that  of  a  chicken,  or  a  monkey  with  human  serum, 
are  procedures  which  usually  do  not  yield  precipi- 
tatino'  serums. 

o 

Chemically,  little  is  kno\ATi  of  precipitins.  They  xatm-e  of 
are  thrown  down  by  ammonium  sulphate  in  con-  Pi'^cipitms, 
Junction  with  the  euglobulin  fraction  of  serum,  and 
are  destroyed  by  those  substances  which  alter  al- 
buminous bodies,  as  acids,  alkalies,  pepsin  and 
trypsin.  That  bacterial  precipitins  are  not  iden- 
tical with  agglutinins  for  the  same  bacteria  is 
shown  b}^  the  following  facts :  Immunization  with 
certain  bacteria  may  produce  agglutinin  but  no 
precipitins.  Precipitins  develop  more  slowly  than 
agglutinins.  As  a  rule  precipitins  are  inactuated 
at  lower  temperatures  than  agglutinins. 

When  serum  is  heated  to  from  50°  to  60°  C.  its   specific 
ability  to  cause  a  precipitate  in  the  homologous 
precipitogen  is  destroyed,  although  it  may  be  dem- 
onstrated that  the  power  to  combine  with  the  lat- 


238  INFECTION     AND     IMMUNITY. 

ter  is  unchanged.  Hence  precipitin,  like  agglu- 
tinin, is  composed  of  two  groups,  a  binding  or 
haptophorous,  and  a  ferment-like  group  in  which 
the  active  property  reside;  the  latter  is  the  coag- 
ulin  of  the  molecule.  When  precipitin  has  lost  its 
coagulin  it  becomes  precipitoid,  and  as  precipitoid 
it  ma}^  unite  with  precipitogen  and  thereby  inhibit 
the  action  of  a  fresh  precipitin  which  may  be 
added  later.  When  a  precipitating  serum  has 
partly  degenerated  into  precipitoids,  that  is,  when 
it  consists  of  a  mixture  of  precipitin  and  precipi- 
toid, it  is  found  that  the  latter  have  the  greater 
affinity  for  precipitogen;  henoe,  in  concentrated 
solutions  of  the  serum,  precipitoid  may  be  present 
in  sufficient  quantity  to  bind  all  the  available  pre- 
cipitogen, and  the  reaction  would  not  occur  in 
spite  of  the  presence  of  active  precipitin.  This  is 
spoken  of  as  specific  'inhibition.  The  action  is 
analogous  to  that  of  toxoids  and  agglutinoids,  and 
the  phenomenon  is  mentioned  again  in  this  in- 
stance in  order  to  emphasize  the  fact  that  certain 
principles  of  action  are  common  to  many  of  the 
immune  substances.  Precipitoids,  like  toxoids  and 
agglutinoids,  are  formed  by  long  standing,  by  the 
action  of  heat  and  light  and  by  other  injurious  in- 
fluences. 

Antiprecip-        '^^hc  molcculc  of  precipitin,  like  that  of  agglu- 
tinin, is  a  receptor  of  the  second  order  (Fig.  6). 

The  attempt  has  been  made  to  produce  antipre- 
cipitins  by  immunization  with  precipitating 
serums ;  this  is  immunization  with  an  immune 
serum.  Tt  is  reported  that  antibodies  have  been 
obtained  for  lactoscrum,  but  not  for  bacterial  pre- 
cipitins. There  is  a  limit  to  the  cycle  of  antibody 
formation. 


itins. 


PRECIPITOGEN.  239 

Prccipitoofen  may  be  defined  as  any  albuminous   xature  of 

.  .  .  .  Precipito- 

substance  immunization  with  whicli  will  cause  the 


sen. 


formation  of  a  specific  precipitating  serum.  In 
addition  to  those  mentioned  above,  albuminous 
urine,  pleural  exudates,  ascitic  fluid  and  that  from 
hydrocele  are  precipitogens.  Tlie  same  is  true  of 
some  albuminous  fractions  of  serums,  as  globulin, 
the  precipitating  serum  for  which  may  be  called 
antiglobulin.  Ivraus  believes  that  the  precipitogen 
of  bacterial  filtrates  is  associated  with  albuminous 
molecules.  Jacoby  obtained  by  tryptic  digestion 
of  ricin,  a  precipitogen  which  gives  no  albumin 
reaction.  On  the  other  hand,  certain  precipito- 
gens are  destroyed  by  pepsin  and  trypsin,  a  fact 
which  indicates  their  albuminous  nature. 

Certain  precipitogens  are  said  to  consist  of  a 
thermolabile  and  a  therrnostabile  portion,  the  dif- 
ferentiation of  which  we  need  hardly  consider. 

It  is  of  no  little  interest  that  precipitogen   simi-   Precipitoid 

,         ,  •     •,•  •   J.         n    L  XT  1      Derived    from 

lar  to  precipitin,  consists  oi  two  groups,  through    preeipitosen. 

one  of  which  it  unites  with  precipitin,  whereas  the 
other  has  a  coagulating  function.  Egg  albumin, 
for  example,  when  heated  to  rather  high  tempera- 
tures, loses  its  ability  to  participate  in  the  pre- 
cipitation reaction,  although  it  retains  its  binding 
power  for  precipitin.  In  view  of  the  fact  that  the 
two  substances  which  enter  into  the  reaction  have 
similar  structures,  it  is  difficult  to  say  which  as- 
sumes the  passive  and  which  the  active  role.  De- 
generated precipitogen  is  also  called  precipitoid. 
In  order  to  distinguish  the  two  precipitoids  one 
must  speak  of  the  precipitoid  of  precipitogen.  and 
the  precipitoid  of  precipitin.  The  precipitoid  of 
precipitogen  yields  precipitin  by  immunization ; 
hence,  it  is  all  the  more  analosrous  to  the  toxoids. 


240  INFECTION     AND     IMMUNITY. 

Precipitate.  The  precipitate  which  is  caused  when  a  bacterial 
filtrate  is  mixed  Avith  its  specific  antiserum  forms 
in  from  one-half  hour  to  several  hours,  and  appears 
as  a  coherent  white  sediment  which  in  tlie  course 
of  twenty-four  hours  has  left  the  overlying  fluid 
quite  clear.  The  action  of  the  precipitins  for 
serums  is  more  rapid,  and  in  either  case  sedimen- 
tation is  hastened  by  placing  the  fluids  at  body 
temperature.  As  intimated  above,  the  occurrence 
of  the  reaction  depends  on  an  intact  condition  of 
the  coagulin  groups  of  both  substances.  A  low 
concentration  of  organic  acid  favors,  whereas  min- 
eral acids  and  alkalies  inhibit  or  prevent  precipi- 
tation ;  a  neutral  reaction  is  indifferent.  The  pre- 
cipitate contains  albumin,  which,  however,  has  be- 
come so  changed  that  it  is  not  susceptible  to  the 
action  of  trypsin.  The  two  in  combining  have  in 
some  way  shut  off  the  point  of  attack  for  trypsin. 
A  lactoserum  precipitates  the  casein  of  the  corre- 
sponding milk.  The  presence  of  salts  is  necessary 
for  the  reaction  of  precipitation.  Both  agglutinin 
and  agglutinogen  are  present  in  the  precipitate, 
but  there  seems  to  be  no  law  governing  the 
amounts  of  each  in  the  combination. 

The  supernatant  fluid  contains  a  remaining 
soluble  part  of  both  substances  as  can  be  shown  by 
adding  fresh  precipitin  and  vice  versa. 
Gronp  Pre-  Group  precipitation  is  not  so  pronounced  as 
*^****s"ecific'iry!  g^oup  agglutination,  yet  it  exists  to  a  certain  de- 
gree and  is  of  the  utmost  practical  importance  in 
attempting  to  differentiate  serums  by  the  precipi- 
tation method.  Although  bacterial  precipitins  are 
highly  specific,  it  is  important  to  observe  the  prin- 
ciple of  serum  dilution  which  was  emphasized 
under  agglutination,  in  order  to  obtain  the  adven- 


PRECIPITINS.  241 

titious   precipitins   in    such   small   amounts   that 
they  do  not  interfere  with  the  chief  precipitin. 

That  feature  of  the  precipitation  reaction  which   Forensic 

Use    of 

has  the  most  practical  bearing  has  to  do  with  its  Pi-ecii»itiii«. 
medicolegal  use  in  the  detection  of  human  blood. 
For  this  purpose  it  has  supplanted  the  specific 
hemolytic  serums,  which  are  to  be  referred  to  later. 
In  the  course  of  investigations  it  was  found  that 
even  the  smallest  dried  blood  stain,  although 
months  old,  would  cause  the  formation  of  a  sedi- 
ment when  mixed  with  its  homologous  precipitat- 
ing serum.  It  remained  for  certain  important  de- 
tails to  be  worked  out  in  order  to  render  the  test 
sufficiently  reliable  for  forensic  work.  The  spe- 
cificity of  the  reaction  appeared  to  be  threatened 
somewhat  when  it  was  learned  that  the  serum  of 
monkeys  undergoes  precipitation  when  treated  by 
an  immune  serum  which  is  specific  for  human 
serum.  This  is,  again,  group  precipitation.  Ad- 
ventitious precipitation  is,  in  fact,  so  widespread 
that  some  have  felt  justified  in  speaking  of  a  mam- 
malian sei'um  reaction.  Hence,  in  order  to  insure 
specificit}^,  it  has  become  necessary  to  use  precise 
quantitative  methods  in  differentiating  bloods  or 
serums  by  this  method.  The  immune  serum  which 
is  used  in  the  test  must  be  diluted  to  some  extent 
in  order  to  eliminate  accidental  precipitins;  but 
even  a  more  important  precaution  is  the  volumet- 
ric measurement  of  the  precipitate  which  is 
formed.  The  technic  of  Schur  may  be  cited.  Test 
tubes  are  so  made  that  the  lowermost  portion  con- 
sists of  a  graduated  capillary  tube.  One  c.c.  of  the 
fluid  to  be  tested  is  placed  in  one  of  these  tubes,  to 
which  is  then  added  0.2  c.c.  of  the  precipitating 
serum.    The  mixture  is  kept  at  body  temperature 


242  IXFECTION     AND     IMMUNITY. 

until  the  reaction  is  complete^  and  the  sediment  is 
then  thrown  into  the  capillary  portion  of  the  tube 
by  centrifugation  for  a  stated  period  of  time 
(twenty  minutes).  The  volume  of  the  sediment 
may  be  read  by  the  scale.  Nuttall  allows  the  sedi- 
mentation to  occur  naturally,  with  the  tubes  in  an 
upright  position.  Other  serums  naturally  must 
be  used  as  controls.  If  the  "unknown"  blood  is 
suspected  of  being  human,  a  control  tube  mijst  be 
prepared  in  wiiich  a  similar  amount  of  known  hu- 
man serum  is  submitted  to  the  same  test.  If  the 
two  tubes  yield  similar  amounts  of  precipitate 
when  they  are  treated  with  0.2  c.c.  of  a  precipi- 
tin which  is  specific  for  human  serum,  the  identity 
of  the  "unknown"  blood  as  that  of  man  is  estab- 
lished. To  obtain  the  specific  precipitin  it  is  cus- 
tomary to  immunize  rabbits  with  human  serum  for 
several  weeks. 
Identification       Another  practical  feature  of  the  precipitation 

of    Meats. 

test  has  to  do  with  the  differentiation  of  meats.  A 
precipitogenous  substance  which  is  characteristic 
for  the  animal  may  be  extracted  or  pressed  from 
the  flesh,  and  will  yield  a  precipitate  when  it  is 
mixed  with  a  precipitin  of  homologous  nature. 
This  is  of  particular  interest  in  those  countries  in 
which  the  meat  of  the  horse  is  put  on  the  market 
as  a  substitute  for  that  of  beef. 
coiioidN  an<i        (For  the  relation  of  precipitins  to  ananhvlaxis 

tlie  Reactions  ,         .  i      i       •     \  '      ' 

of  immnnity.   sec  Chapter  ou  anaphylaxis.) 

In  view  of  the  fact  that  the  protoplasm  of  the 
body  and  the  albuminous  constituents  of  serum 
liave  a  close  relationship  to,  or  really  are,  colloids, 
investigators  have  studied  certain  reactions  which 
occur  among  the  known  colloids  with  the  expecta- 
tion that  the  reactions  of  protoplasm  and  those  of 


Colloids. 


COLLOIDS.  243 

serums  would  receive  some  elucidation.  iSTot  much 
advancement  can  be  made,  however,  until  the  prop- 
erties of  colloids  are  more  thoroughly  understood. 
Substances  which  go  into  solution  were  classi- 
fied b}'  the  English  physicist,  Graham^  as  crystal- 
loids and  colloids.  Crystalloids  include  many  in- 
organic salts.  Usually  they  form  clear  solutions 
in  water  and  exert  osmotic  pressure,  supposedly 
because  of  the  small  size  of  their  molecules.  They 
diffuse  with  some  rapidity  and  many  are  conduc- 
tors of  electricity.  Organic  colloids  comprise  such 
substances  as  albumin,  starch,  dextrin,  tannin, 
gelatin  and  many  g-ums.  By  proper  treatment  of 
certain  metals  and  their  salts,  inorganic  colloids  properties  of 
may  be  prepared ;  for  example,  ferric  hydroxid  and 
the  sulphids  of  antimony  and  arsenic.  "^Tien  col- 
loids are  dissolved  in  water  the  solutions  are  often 
more  or  less  opaque,  and  are  sometimes  opalescent 
because  the  particles  or  molecules  are  of  such  size 
that  they  polarize  light.  They  exist  in  water  either 
as  a  solution  of  molecules  of  great  size  or  as  a  sus- 
pension of  considerable  particles  or  aggregates  of 
molecules.  In  some  instances  the  particles  are  so 
large  that  they  may  be  seen  by  a  magnification  of 
1,000  diameters,  while  in  others  no  degree  of  mag- 
nification renders  them  visible  mth  the  ordinary 
microscope.  By  the  use  of  the  recently  devised 
ultramicroscope,  however,  the  finest  particles  in 
some  colloidal  solutions  may  be  discerned.  Col- 
loidal substances,  such  as  albumin,  diffuse  very 
slowly  and  exert  little  or  no  osmotic  i^ressure,  sup- 
posedly because  of  the  large  size  of  the  particles. 
They  do  not  conduct  electricity,  but  the  particles 
themselves  react  to  the  electric  current  by  altera- 
tions in  the  direction  of  their  motion  (i.  e.,  toward 


244  IXFECriON     A^D     IMMUNITY. 

^  the  positive  or  the  negative  pole),  and,  moreover, 
carr}^  electric  charges  themselves. 
Precipitation  Tlic  featurcs  of  colloids  wMch  bring  them  into 
** Electrolytes^  relation  with  the  subject  in  hand  are  their  coagu- 
lable  nature  in  certain  instances  and  the  fact  that 
their  particles  may  be  agglutinated  or  precipi- 
tated by  the  addition  of  minute  amounts  of  salts 
(electrolytes).  In  this  connection  one  naturally 
recurs  to  the  observation  of  Bordet,  which  was 
mentioned  in  the  preceding  chapter,  concerning 
the  inagglutinability  of  micro-organisms  so  long 
as  salt  is  withheld  from  the  solution.  This  anal- 
ogy would  suggest  that  the  bacteria  after  their 
union  with  agglutinin  may  conduct  themselves  as 
colloidal  particles.  In  the  precipitation  of  colloids 
by  salts  it  has  been  suggested  that  the  salts  so 
alter  the  electric  condition  of  the  colloidal  parti- 
cles that  their  surface  tension  is  decreased,  and  as 
a  result  of  this  change  neighboring  particles 
coalesce  in  such  quantities  as  to  produce  a  visible 
sediment. 

Xeisser  and  Friedberger  have  studied  certain 
colloids,  having  in  mind  the  similarity  of  their  be- 
havior to  serum  reactions.  They  found,  for  exam- 
ple, that  two  of  our  common  dyes  which  are  col- 
loids and  bear  opposite  charges  of  electricity  (eosin 
and  Bismarck  brown),  give  rise  to  a  precipitate 
when  the  two  are  mixed.  Furthermore,  the  spe- 
cific inhibition  which  may  be  obtained  in  the  reac- 
tion with  serum  precipitins  (see  above)  could  also 
be  realized  with  the  eosin  and  Bismarck  brown. 

The  agglutination  of  bacteria  and  of  red  blood 
cells  may  also  be  accomplished  with  colloids, 
liandsteiner  agglutinated  erytl^rocytes  with  col- 
loidal silicic  acid. 


CHAPTER  XVI. 


A.   GENERAL   PROPERTIES  OF   BACTERICIDAL 
SERUMS. 

Antibacterial,  bactericidal  and  bacteriolytic  are  Bacteriolysis 
three  terms  which  are  used  in  a  rather  loose,  inter-  ?ysin.  ***' 
changeable  way,  although  they  are  not  strictly 
synonymous.  A  bactericidal  serum  is  one  which  is 
able  to  kill  bacteria,  as  the  term  implies ;  if  at  the 
same  time  it  dissolves  the  organisms  it  is  bacterio- 
\jtic.  Inasmuch  as  some  serums,  as  antityphoid, 
do  kill  bacteria  without  dissolving  them,  w^hile 
others,  as  anticholera,  have  the  dissolving  power, 
the  distinction  has  a  certain  significance.  In  either 
case  the  serum  is,  of  course,  antibacterial.  For 
lack  of  a  more  concise  English  term,  bacteriolysis 
is  used  to  designate  the  process  in  which  bacteria, 
with  or  without  solution,  are  killed  by  serums. 
Bacteriolysin  refers  to  the  substances  in  serum 
which  accomplish  this  action.  The  means  of  de- 
termining the  bactericidal  power  of  a  serum  are 
indicated  on  page  254.  True  bacteriolysis  is  best 
observed  with  the  organism  of  cholera  and  its 
antiserum  as  described  later  under  the  title  of  the 
Pfeiffer  experiment. 

Bacteriolysins  are  far  more  complex  than  anti- 
toxins, agglutinins  and  precipitins.  One  may  best 
appreciate  their  nature  as  understood  at  present 
by  tracing  their  development  from  the  relatively 
simple  alexins  of  Buchner. 

Following  the  investigations  of  Fodor,  Behring  Alexins. 
and  others,  which  showed  that  normal  blood  mav 


246  INFECTION     AND     IMMUNITY. 

kill  bacteria  in  the  test-tube,  and  after  additional 
facts  were  obtained  by  Nnttall,  Bnchner  demon- 
strated that  it  is  not  necessary  to  use  the  full  blood 
in  order  to  obtain  the  bactericidal  action,  but  that 
serum  alone  has  a  similar  effect.  He  spoke  of  the 
antibacterial  substances  collectively  as  alexins 
(substances  which  ward  off),  taking  the  reason- 
able Aiew  that  natural  immunity  to  bacteria  de- 
pends on  their  presence  in  the  bod^y.  The  increased 
bactericidal  power  of  the  serum  which  develops 
during  immunization  or  infectic^i  with  certain 
micro-organisms  goes  hand  in  hand  with  the  in- 
creased resistance  of  the  individual  against  the 
infection.  The  alexins  have  undergone  a  specific 
increase;  they  are  now  immune  alexins  or,  as  we 
say  to-day,  immune  bacteriolysins,  and  it  is  sup- 
posed that  acquired  immunity,  in  these  instances, 
depends  on  their  new  formation. 
Selective       Alcxius  werc  vcry  sensitive  substances ;  they  dis- 

Aetioii.  1  1  ^        ^  •  p 

appeared  spontaneously  irom  serums  m  a  lew 
days,  were  destroyed  by  a  rather  low  degree  of 
heat  (55°  C),  by  acids  and  alkalies,  and  were 
active  only  in  the  presence  of  certain  salts,  espe- 
cially sodium  chlorid.  A  striking  feature  of 
alexins,  as  distinguished  from  chemical  bacteri- 
cides, was  their  marked  selective  action  on  bac- 
teria. The  alexins  of  animal  A  might  destroy  one 
micro-organism  readily  and  affect  another  little  or 
none  at  all,  whereas  those  of  animal  B  might  have 
different  selective  characteristics. 
The  phenoin-       "Work  which  was  instituted  by  Pfeiffer  and  de- 

eiioii    of  TP1  1  1  11      i 

pfeiflfer.  velopcd  furthcr  by  others  led  the  Avay  to  a  more 
correct  understanding  of  the  nature  of  alexins. 
Pfeiffer  studied  the  bactericidal  action  of  serums 


PFEIFFER'S     PHENOMEXOX.  247 

in  the  body  of  the  living  animal,  i.  e.,  in  the  peri- 
toneal cavity.  His  most  classic  results  were  ob- 
tained with  the  organism  of  cholera.  A  guinea- 
pig  is  immunized  against  this  micro-organism  by 
injections  of  the  killed  or  living  bacteria.  We  have 
already  learned  of  this  process  as  that  of  active 
antibacterial  immunization.  When  the  animal  is 
well  immunized  the  experiment  is  begun  by  the 
intraperitoneal  injection  of  a  quantity  of  culture 
which  would  be  fatal  to  an  unimmunized  animal. 
At  intervals  during  the  next  twenty  or  thirty  min- 
utes small  amounts  of  peritoneal  fluid  are  removed 
for  .microscopic  examination  by  means  of  fine 
pipettes  which  have  been  drawn  out  in  the  flame. 
The  abdominal  wall  is  punctured  with  the  pi- 
pette through  an  incision  in  the  skin  and  the 
fluid  flows  into  the  tube  by  capillary  attraction. 
A  portion  of  the  fluid  is  examined  as  a  hanging- 
drop  or  dried  on  a  cover-glass,  fixed  in  the  flame 
and  stained  with  a  dilute  solution  of  carbol- 
fuchsin.  In  the  hanging-drop  it  is  first  noticed 
that  the  organisms  have  lost  their  motility;  the 
comma-shaped  and  S-shaped  forms  soon  become 
spherical  and  at  first  appear  swollen  and  clear, 
whereas  in  later  preparations  they  gradually  de- 
crease in  size  and  show  a  very  rapid  vibrating 
movement,  the  so-called  Brownian  movement, 
which  is  purely  physical  in  nature.  In  the  course 
of  from  twenty  to  thirty  minutes  the  organisms 
have  been  completely  dissolved.  These  changes 
may  be  followed  in  the  stained  specimens,  in  which 
the  altered  cells  eventually  appear  as  fine  red 
granules. 

As  Metchnikoff,  Bordet  and  others  have  shown,   Tiie  Experi- 
the  same  result  mav  be  obtained  without  the  inter- 


by     the     Tis- 
sues. 


248  INFECTION     AND     IMMUNITY. 

vention  of  the  animal  body,  by  mixing  perfectly 
fresh  anticholera  serum  with  the  vibrios  and 
mounting  as  a  hanging-drop  preparation.  The 
slide  must  be  kept  at  the  temperature  of  the  body 
by  means  of  a  warm  stage.  The  reaction,  how- 
ever, is  far  less  vigorous  than  when  it  takes  place 
in  the  peritoneal  cavity  and  the  solution  of  the 
cells  may  not  be  complete.  No  bacterium  is  so 
completely  dissolved  under  these  conditions  as  the 
vibrio  of  cholera,  although  the  typhoid  bacillus  and 
similar  organisms  undergo  some  changes  in  their 
form. 
The  Activa-  Tlic  experiment  of  Pfeiffer  may  also  be  con- 
a'cUve  seruVu  ductcd  in  the  abdominal  cavity  of  a  non-immune 
guinea-pig  by  injecting  anticholera  serum  in  con- 
jiinction  wdth  the  culture  (passive  antibacterial 
immunization) .  This  is  the  classic  Pfeiffer  experi- 
ment. The  immune  serum  should  be  of  such 
strength  and  should  be  given  in  such  quantity  that 
the  animal  is  saved  in  spite  of  the  ten  fatal  doses 
of  culture  which  the  typical  experiment  demands. 
Experiments  brought  to  light  a  condition  which 
seemed  paradoxic;  an  old  immune  serum  which 
had  lost  its  bactericidal  power  as  manifested  in 
vitro,  or  one  in  which  the  alexins  had  been  de- 
stroyed by  a  temperature  of  60°  C,  showed  its 
original  protective  power  in  the  animal  experi- 
ment. Furthermore,  when  an  inactive  immune 
serum  was  injected  into  the  abdominal  cavity,  al- 
lowed to  remain  for  a  time  and  then  withdrawn, 
its  bactericidal  power  for  experiments  in  vitro  was 
found  to  be  re-established.  On  the  basis  of  these 
facts,  Pfeiffer  concluded  that  the  specific  sub- 
stance is  present  in  the  immune  serum  in  an  inac- 
tive form,  and  that  it  becomes  active  as  a  result 


PFEIFFEWS     PHENOMENON.  249 

of  contact  with  living  tissue  cells,  supposedly  the 
endothelial  cells  of  the  peritoneum.  According  to 
this  conclusion,  an  inactive  serum  could  become 
active  again  only  after  its  introduction  into  the 
body. 

It  remained  for  Bordet  to  show,  on  the  con-   inactivation 

,  .  -,       ami    Reacfiva- 

trar}^,  that  contact  of  the  serum  with  living  cells  tion. 
is  not  necessary  to  render  it  active  for  bacterici- 
dal experiments  in  vitro.  It  is  sufficient  to  add 
to  the  heated  immune  serum  a  small  amount  of 
fresh  normal  serum  from  some  normal  animal, 
the  quantity  of  normal  serum  which  is  used  not 
being  in  itself  bactericidal.  Under  these  condi- 
tions, then,  we  have  to  do  with  two  serums  which, 
when  combined,  are  bactericidal,  but  when  sepa- 
rated are  inactive.  The  destruction  of  the  active 
property  of  a  serum  by  heat  or  by  other  means  is 
called  inactivation,  and  the  re-establishment  of  its 
power  by  the  addition  of  fresh  normal  serum  is 
reactivation.  The  immune  serum,  when  heated  to 
55  to  60°  C,  loses  something  which  is  essential  to 
its  activity,  and  this  something  may  be  replaced 
by  the  normal  serum.  That  the  substance  in  the 
normal  serum  is  identical  with  that  which  was  de- 
stroyed in  the  immune  serum  is  indicated  by  the 
fact  that  it  is  destroyed  by  the  same  degree  of 
heat;  a  heated  normal  serum  will  not  reactivate 
an  immune  serum. 

The  conclusion  of  Bordet  that  the  bactericidal  Two  sub- 
power  of  a  serum  depends  on  the  combined  action  isactericidai 
of  two  substances  has  been  substantiated  by  numer- 
ous investigators.  These  are  the  substances  which 
in  recent  years  have  become  familiar  under  the 
names  of  amboceptor  and  complement  and  their 
various  synonyms  (see  p.  256).    One  of  them,  the 


Serum. 


250 


INFECTION     AND     IMMUNITY. 


Specificity 


Group      Reac- 
tion. 


amboceptor,  is  heat-resistant  (thermostabile),  i.  e., 
it  is  not  destroyed  at  56°  C,  whereas  the  other, 
the  complement,  is  susceptible  to  heat  (therm o- 
labile),  being  destroyed  at  that  temperature  which 
killed  the  alexins  of  Buchner.  The  term  alexin 
is  still  applied  by  some  writers  to  the  thermolabile 
substance  (complement),  its  original  significance 
havino-  been  modified. 

The  specificity  which  prevails  among  antitoxma 
and  agglutinins  is  found  also  in  the  action  of  bac- 
tericidal serums.  When  an  anticholera  serum  is 
injected  into  the  peritoneal  cavity  of  a  guinea- 
pig,  protection  is  not  afforded  against  other  vibrios 
or  other  pathogenic  organisms.  The  specificity  is 
so  great  that  the  reaction  of  Pfeiffer  may  be  used 
for  the  identification  of  bacteria.  If  one  has  in 
hand  an  unloiown  vibrio,  its  identity  or  non-iden- 
tity as  the  organism  of  cholera  may  be  determined 
by  injecting  it,  in  conjunction  with  anticholera 
serum,  into  the  peritoneal  cavity  of  a  normal 
guinea-pig;  if  the  microbe  is  transformed  into 
granules  it  is  the  vibrio  of  cholera,  otherwise  it  is 
not.  Other  bacteria  may  be  identified  in  a  similar 
manner  by  the  use  of  the  proper  serums.  In  spite 
of  this  high  specificity,  the  group  reaction  may 
occur  even  with  bactericidal  serums.  An  anti- 
typhoid serum,  for  example,  shows  its  strongest 
bactericidal  power  for  the  typhoid  bacillus,  al- 
though it  is  at  the  same  time  more  destructive  for 
closely  related  organisms,  as  the  colon  bacillus, 
than  a  normal  serum  from  the  same  species.  By 
diluting  the  serum  sufficiently  the  adventitious 
bacteriolysins  are  so  nearly  eliminated  that  the 
specificity  of  the  serum  for  its  homologous  organ- 
ism becomes  manifest. 


BACTERICIDAL     SERUMS.  251 

Bactericidal  serums  are  not  obtained  with  equal 
readiness  for  all  micro-organisms.  We  are  most 
familiar  with  those  which  are  yielded  by  immuni- 
zation or  infection  with  the  microbes  of  cholera, 
typhoid,  plague,  the  colon  bacillus  and  related  bac- 
teria. Many  other  bacteria,  as  the  pneumococcus, 
streptococcus,  tubercle  bacillus  and  others,  yield 
neither  antitoxins  nor  bactericidal  substances.  In- 
asmuch as  recovery  from  such  infections  is  an  ex- 
pression of  acquired  immunity,  no  matter  how 
temporary  it  may  be,  it  is  evident  that  not  all  ex- 
amples of  acquired  immunity  can  be  explained  on 
the  basis  of  the  serum  properties  which  we  now 
recognize.  This  will  be  referred  to  again  in  rela- 
tion to  phagocytosis  (Chapter  XYIII). 

Experiments  of  some  importance  have  to  do 
with  the  ability  of  bacteria  to  absorb  the  homolo- 
gous bactericidal  substance  from  a  serum  when  the 
two  are  mixed  in  test-tubes.  Hence,  if  natural 
antibacterial  immunity  depends  on  the  bacterioly- 
sin  which  is  present  in  the  circulation,  a  large 
mass  of  the  bacterium,  when  injected  intravenously 
should  absorb  or  fix  the  bactericidal  substances ;  as 
a  consequence,  serum  which  is  drawn  later  should 
show  a  great  decrease  in  its  bactericidal  power  for 
the  organism  which  was  injected.  Although  re- 
sults of  this  nature  have  been  obtained  by  a  num- 
ber of  competent  investigators,  they  are  not  with- 
out exception.  In  the  same  connection  fatal  infec- 
tions should  be  accompanied  by  a  decrease  of  the 
natural  bactericidal  power  of  the  serum  for  the 
organism  involved.  This  has  been  found  to  be  true 
in  man  in  relation  to  plague,  and  in  some  animal 
infections. 


Kiidotoxins. 


252  IXFECTION     AXD     IMMUNITY. 

The  Effect  of  In  a  preceding  chapter  micro-organisms  were 
Serums*  "n  diviclcd,  fiist,  into  those  which  secrete  soluble  tox- 
ins, immunization  with  which  causes  the  forma- 
tion of  antitoxins,  and,  second,  those  which  do  not 
secrete  such  toxins  and  for  which  no  manipula- 
tions known  at  the  present  time  are  successful  in 
stimulating  to  the  formation  of  antitoxins.  These 
lines,  however,  can  not  be  drawn  sharply,  for  there 
are  a  few  micro-organisms  which,  according  to 
manipulation,  cause  the  formation  of  either  an 
antitoxic  serum  or  a  bactericidal  serum.  In  gen- 
eral it  may  be  said  that  the  character  of  the  serum 
depends  on  the  bacterial  constituent  which  is  used 
for  immunization.  If  the  diphtheria  bacillus  it- 
self, or  the  pyocyaneus  bacillus,  is  injected,  the 
toxin  having  been  washed  away,  bactericidal  ser- 
ums are  formed,  whereas  if  toxins  alone  are  intro- 
duced, antitoxins  are  the  result.  After  all,  it 
seems  plain  that  the  bacteria  of  the  second  group 
must  be  pathogenic,  because  of  toxic  substances 
which  they  carry  with  them  into  the  body.  In 
view  of  the  fact,  however,  that  they  do  not  secrete 
soluble  toxins  in  culture  media,  it  is  held  that 
their  toxic  properties  are  integrally  associated  with 
the  bacterial  protoplasm;  they  are  the  endotoxins 
spoken  of  previously. 

The  question  naturally  arises:  Does  a  bacteri- 
cidal serum  in  dissolving  or  killing  its  homologous 
organism  neutralize  the  endotoxin  at  the  same 
time?  On  the  basis  of  very  positive  experiments 
which  have  been  performed,  especially  by  Pfeiffer, 
it  is  evident  that  the  senim  has  no  such  action.  In 
the  experiment  of  Pfeiffer,  one  may  inject  into  the 
abdomen  a  sufficient  quantity  of  anticholera  serum 


BACTERICIDAL     SERUMt^.  253 

to  kill  all  the  organisms  which  have  been  intro- 
duced, and  yet  the  animal  may  die  with  the  intoxi- 
tion  of  cholera.  Furthermore,  if  one  considers  a 
culture  of  the  cholera  vibrio,  which  has  been  killed 
by  heat,  as  representing  so  much  cholera  toxin, 
anticholera  serum  protects  against  no  more  of  it 
than  does  the  same  quantity  of  normal  serum.  It 
is  believed  that  anticholera  and  similar  immune 
sernms  may  even  increase  intoxication  by  dissolv- 
ing the  bacteria  and  thus  liberating  an  excess  of 
endotoxin. 

We  have  little  positive  knowledge  concerning  the  orisin  of 

^  .    .  .        Bactericidal 

organs  which  form  the  bactericidal  substances  in  substances. 
acquired  immunity.  Pfeiffer  and  Marx,  in  rela- 
tion to  cholera,  and  Wassermann  in  typhoid,  found 
that  the  spleen  and  the  hemopoietic  organs  in  gen- 
eral contain  the  immune  bodies  in  greater  concen- 
tration than  the  blood  serum,  and  in  immunization 
experiments  the  bodies  may  be  demonstrated  in 
these  organs  at  a  time  when  they  are  absent  from 
the  circulation.  This  fact  is  generally  accepted  as 
proof  of  their  formation  at  these  points.  Wasser- 
mann and  others  have  demonstrated  the  presence 
of  complement  in  the  leucocytes,  and  Metchnikoff 
holds  that  it  is  produced  only  by  such  cells.  (See 
origin  of  agglutinins,  Chapter  XIII.) 

The  standardization  of  bactericidal  serums  is  at  Jta".»iard- 
present  more  of  theoretical  than  of  practical  in- 
terest, because  of  their  limited  therapeutic  use. 
Their  values  can  not  be  determined  with  the  ac- 
curacy with  which  one  measures  a  unit  of  anti- 
toxin. One  may  deliver  from  a  pipette  a  definite 
quantity  of  toxin  and  if  the  toxin  has  been  well 
preserved  the  same  quantit}''  may  be  obtained  at 


254  INFECTION     AND     IMMUNITY. 

any  subsequent  time.  On  the  other  hand,  it  is  impos- 
sible to  preserve  a  culture  of  living  bacteria  so  that 
the  number  of  the  organisms  and  the  virulence 
of  the  culture  remain  constant,  nor  will  two  cul- 
tures made  at  different  times  contain  the  same 
number  of  cells  in  a  given  volume.  Hence,  stand- 
ard cultures  which  are  necessar}^  for  the  systematic 
valuation  of  serums  are  not  easily  available.  One 
may  use  a  definite  volume  of  a  bouillon  culture  of 
an  organism  which  has  grown  for  a  certain  number 
of  hours,  but  in  all  likelihood  no  two  cultures 
would  contain  the  same  number  of  organisms. 
Pfeiffer  uses  the  normal  loop  which  has  been  men- 
tioAed,  i.  e.,  one  which  will  take  up  from  a  surface 
of  agar  two  milligrams  of  the  bacterial  mass.  The 
culture  must  have  grown  for  a  definite  period, 
eighteen  to  twenty-four  hours.  Tests  having  some 
value  may  be  made  in  the  test-tube  with  the  fresh 
or  complemented  serum.  This,  however,  gives  one 
only  the  bactericidal  power  as  it  is  manifested  out- 
side the  bod}^,  and  it  may  not  be  a  correct  index  of 
the  protective  power  of  the  serum  when  it  is  in- 
jected into  the  living  animal.  For  the  test-tube 
experiment  various  dilutions  of  the  serum  are 
made,  as  1  to  10,  1  to  100  and  1  to  1,000^  and  a 
similar  quantity  of  each  dilution,  properly  comple- 
mented, is  mixed  with  a  given  mass  of  the  culture ; 
the  mixtures  are  then  placed  in  the  thermostat  for 
a  number  of  hours.  At  the  end  of  this  time  plate 
cultures  are  made  from  each  of  the  mixtures,  the 
plates  put  aside  for  twenty-four  hours,  and  the 
colonies  which  have  developed  are  then  counted. 
The  quantity  of  serum  required  to  kill  all  the  bac- 
teria may  be  taken  as  the  basis  for  computing  its 
bactericidal  value. 


BACfERWIDAL     SERUMS.  255 

When  the  protective  power  of  the  serum  is  de- 
termined by  animal  experiment  it  is  not  essential 
to  use  the  serum  when  fresh;  in  fact,  the  native 
complement  in  the  immune  serum  may  be  disre- 
garded, or,  preferabl}^,  it  may  be  destroyed  by  heat. 
If  the  latter  procedure  is  adopted,  or  if  an  old 
serum  is  used  in  which  the  complement  has  de- 
generated, its  reactivation  is  accomplished  through 
the  complement  which  is  present  in  the  body  of  the 
experiment  animal.  There  are  reasons  for  believ- 
ing that  a  given  antiserum  requires  a  particular 
complement  for  its  reactivation,  and  that  this 
complement  may  be  present  in  some  animals  and 
absent  in  others;  this  will  be  referred  to  again. 

To  find  the  value  of  anticholera  serum  Pfeiffer 
prepares  dilutions  similar  to  those  mentioned 
above,  and  to  the  same  quantity  of  each  dilution 
adds  ten  fatal  doses  of  a  virulent  culture  of  the 
vibrio  of  cholera.  These  are  injected  into  the 
peritoneal  cavities  of  guinea-pigs  and  after  periods 
of  from  forty  to  sixty  minutes  hanging-drop  prep- 
arations are  made  from  the  peritoneal  fluid  of  each 
animal  to  determine  the  formation  of  the  charac- 
teristic granules ;  the  highest  dilution  which  causes 
this  change  in  the  cells  stamps  the  value  of  the 
serum.  The  animal  must  at  the  same  time  be  pro- 
tected against  the  ten  fatal  doses  of  the  culture. 

The  value  of  an  antityphoid  serum  may  be  de- 
termined in  the  same  way,  the  result  being  judged 
by  the  protection  which  is  afforded  the  animal 
rather  than  by  the  formation  of  granules. 

Antityphoid,  antiplague,  and  some  other  serums 
are  also  tested  by  injecting  the  serum  twenty-four 
hours  in  advance  of  the  culture. 


256  INFECTION     AND     IMMUNITY. 

It  is  necessary  to  know  the  virulence  of  a  cul- 
ture with  which  an  antiserum  is  tested.  It  is  pos- 
sible to  maintain  some  organisms  at  a  rather  con- 
stant virulence  by  passage,  i.  e.,  infecting  animals 
with  the  microbe  and  recultivating  it  from  the 
tissues.  With  others,  abundant  controls  must  be 
made  at  the  time  the  serum  is  tested  in  order  to 
know  at  that  moment  the  nrecise  virulence  of  the 
culture.  In  all  probability  it  requires  more  serum 
to  protect  against  very  virulent  cultures  than 
against  those  of  less  virulence. 

B.      HEMOLYSINS. 

Exiieriiiientai  xhc  simplicity  of  hcmolytic  experiments  and  the 
Hemolysins,  rapidity  with  which  they  may  be  performed  and 
terminated  have  rendered  hemol3^tic  serums  par- 
ticularly useful  in  the  study  of  amboceptors  and  of 
complements,  for  we  are  to  understand  that  such 
serums  are  toxic  to  erythrocytes  only  because  of 
the  amboceptors  and  complements  which  they  con- 
tain. The  most  important  facts  which  have  been 
learned  concerning  the  action  of  hemolytic  serums 
have  been  found  to  hold  true  for  bactericidal 
serums  as  well;  hence  it  is  an  indifferent  matter 
if  principles  which  are  common  to  both  are  illus- 
trated by  frequent  references  to  serum-hemolysins. 
Tec-hnic    of       ^]-^q  corDusclcs  for  liemolvtic  experiments  arc 

Hemolytic  ^  -^  f      <>  i       -i 

i^xiieriment.  obtained  by  the  defibrination  of  freshly-drawn 
blood  and  the  removal  of  the  fibrin.  Usually  they 
are  made  into  a  5  per  cent,  suspension  by  dilution 
with  isotonic  (physiologic)  salt  solution.  Inas- 
much as  the  serum  which  is  present  may  interfere 
'  with  the  action  of  the  complement  or  amboceptors 

of  the  hemolysin,  it  is  customary  to  remove  it  by  a 
washing  process.    The  5  per  cent,  emulsion,  or  tlie 


HEMOLYSINS.  257 

undiluted  blood  is  centrifugated,  the  overlying 
fluid  drawn  off  by  means  of  a  pipette  and  substi- 
tuted by  fresh  salt  solution;  the  corpuscles  are 
thoroughly  mixed  with  the  new  solution  and  the 
process  of  centrifugation  repeated^  the  corpuscles 
finally  being  diluted  to  the  original  volume  with 
salt  solution.  After  from  two  to  four  washings 
any  residual  serum  usually  may  be  disregarded. 
To  test  the  hemolytic  power  of  a  serum  one  meas- 
ures identical  quantities  of  the  5  per  cent,  washed 
blood  into  each  of  a  series  of  test-tubes  by  means 
of  a  graduated  pipette  and  then  adds  increasing 
quantities  of  the  serum  to  succeeding  tubes.  All 
tubes  are  then  diluted  to  equal  volumes  by  means 
of  salt  solution^  as  it  is  of  some  importance  to 
maintain  a  uniform  concentration  of  the  cor- 
puscles. The  contents  of  the  tubes  are  mixed 
evenly  by  shaking  and  the  series  is  placed  in  the 
thermostat  for  about  two  hours;  this  temperature 
is  necessary  for  complete  and  rapid  action  of  the 
toxic  substances.  At  the  end  of  this  time  the  tubes 
are  placed  in  the  ice  chest  and  left  over  night  in 
order  that  the  cells  may  settle  to  the  bottom,  or 
sedimentation  may  be  accomplished  at  once  by 
centrifugation. 

In  either  case,  the  overlying  fluid  is  colored  red  Hemoiysij*. 
by  the  dissolved  hemoglobin  in  proportion  to  the 
extent  of  destruction  of  the  erythrocytes.  In  case 
solution  has  been  complete,  the  sediment  is  indis- 
tinct and  colorless,  being  made  up  only  of  the 
stromata  of  cells,  whereas  in  the  tubes  showing 
only  partial  hemolysis  the  sediment  is  red  and  has 
an  indirect  quantitative  ratio  to  the  coloration  of 
the  overlying  fluid.  By  suitable  variations  in  the 
amounts   of   serum   used   in    different   tubes,   its 


258  INFECTION     AND     IMMUNITY. 

exact  dissolving  dose  for  the  given  volume  of  cor- 
puscles may  be  determined.  Although  the  term 
hemolysis  is  a  perfectly  proper  one,  we  are  to  un- 
derstand that  serums  cause  solution  of  the  hemo- 
globin, but  not  solution  of  the  whole  cell ;  we  speak 
loosely  of  solution  of  the  corpuscles. 
Similarity  After  Bordct  had  shown  the  analogy  between 
Bactericidal  bactcricidal  and  hemolytic  serums,  and  after  the 
lytic  Axjtion".  phenomena  of  inactivation  and  reactivation  had 
been  developed  by  Bordet  and  Metchnikoff,  Ehrlich 
and  Morgenroth  undertook  the  study  of  ambocep- 
tors and  complements  as  they  occur  in  hemolytic 
serums.  The  facts  ascertained  by  them  and  the 
methods  of  research  which  they  devised  have  pro- 
vided many  investigators  with  a  starting  point  for 
work  of  the  highest  importance  concerning  the 
bactericidal  serums  and  antibacterial  immunity, 
and  their  interpretations,  moreover,  served  to  ex- 
tend the  side-chain  theory  of  immunity  to  its  pres- 
ent comprehensive  limits. 

For  the  sake  of  convenience  one  may  speak  of  a 
heated  immune  serum,  or  one  in  which  the  com- 
plement has  become  inactive  from  age,  as  a  solu- 
tion of  amboceptors,  disregarding  temporarily  the 
agglutinins,  precipitins  and  perhaps  other  bodies 
which  the  serum  contains.  Also,  since  fresh  nor- 
mal serums  are  rich  in  complements  and  usually 
contain  but  a  small  amount  of  any  one  amboceptor, 
they  may  conveniently  be  considered  as  solutions 
of  complements;  yet  normal  serums  may  not  be 
considered  as  pure  complement  and  used  as  such 
in  unlimited  quantities  for  actual  experiments,  be- 
cause of  the  bacteriolysins  and  hemolysins  which 
many  contain.  Only  a  quantity  of  the  normal 
serum  which  in   itself  is  not  toxic   for  the  cell 


HEMOLYSINS. 


259 


may  be  used  for  complementing  purposes,  and  this 
may  be  as  low  as,  or  lower  than,  0.1  c.c.  for  a  par- 
ticular experiment.  ^ 

As  pointed  out  in  the  preceding  chapter,  the 
combined  action  of  amboceptor  and  complement  is 
necessary  for  the  cytotoxic  action  of  a  serum.  In 
view  of  the  fact  that  the  toxic  power  is  lost  by  ex- 
posure to  that  temperature  Avhich  destroys  comple- 
ment, it  seems  that  the  latter  is  the  actual  dis- 
solving or  toxic  substance,  whereas  the  ambocep- 
tor must  play  some  intermediary  role.  Investiga- 
tions have  shown  that  the  two  act  together  in  a 
very  definite  manner  in  that  the  absorption  of  the 
amboceptors  by  the  cells  is  a  prerequisite  for  the 
absorption  and  action  of  the  complement.  This 
may  be  verified  by  simple  experiments :  Mix 
erythrocytes  with  the  homologous  amboceptors, 
and  after  a  period  of  from  twenty  to  thirty  min- 
utes centrifugate  the  mixture  and  remove  all  the 
free  serum  from  the  cells  by  repeated  washings 
with  isotonic  salt  solution.  If  the  cells  are  again 
suspended  in  salt  solution  and  a  small  amount  of 
complement  is  added  and  thoroughly  mixed,  the 
hemoglobin  is  dissolved  out;  a  control  must,  of 
course,  show  that  the  complement  alone  has  not 
the  dissolving  power.  The  result  indicates  that 
the  erythrocytes  during  their  contact  with  the  im- 
mune serum  had  absorbed  or  combined  chemically 
with  the  amboceptors,  and  that  the  latter  remained 
attached  to  the  cells  in  spite  of  the  washings  to 
which  they  were  submitted. 

It  would  seem  that  the  union  of  amboceptor 
with  cell  has  the  effect  of  rendering  the  latter  sus- 
ceptible to  the  action  of  complement,  and  for  this 
reason  amboceptor-laden   cells   are  spoken  of  as 


The   Absorp- 
tion  of  Am- 
boceptors   by 
Cells, 


Sensitiza- 
tion. 


260  INFECTION     AND     IMMUNITY. 

sensitized  cells.    Hence,  according  to  the  cells  and 
serums    employed,    we    may    refer    to    sensitized 
*-  erythrpcytes,  sensitized  bacteria,  etc.     The  experi- 

ment is  called  the  sensitizing,  absorption  or  bind- 
ing experiment.     An  immune  serum  may  be  de- 
prived of  all  its  amboceptors  in  the  binding  ex- 
periment if  a  sufficient  quantity  of  cells  has  been 
used,  and  it  would  thereby  be  rendered  incapable 
of  further  reactivation  by  the  subsequent  addition 
of  complement. 
r    Order   *^^ij«-       If,  instead  of  performing  the  experiment  in  the 
ceptor   and   manner  described,  the  process  is  reversed  so  that 
omp  emen  .   ^^^^  corpusclcs  are  first  treated  with  the  solution 
of  complement  and  then  with  the  amboceptors,  the 
corpuscles  are  not  hemolyzed.     During  the  wash- 
ing process  the  complement  is  entirely  separated 
from  the  cells,  and  from  this  fact  it  is  clear  that 
direct  union  between  corpuscle  and  complement 
does  not  occur;  only  sensitized  cells  take  up  com- 
plement. 
€ytopiiiiou«       The  question  as  to  whether  the  corpuscles  in 
t?ie**Ain?>o-   taking  up  amboceptors  do  so  by  chemical  combina- 
tion or  by  physical  absorption  has  been  contended 
with  some  vigor.    Ehrlich  believes  that  the  process 
is  one  of  chemical  union,  and  if  one  adheres  to  this 
view  it  becomes  necessary  to  assign  binding  or 
haptophorous  groups  both  to  the  red  blood  cells 
and  to  the  amboceptors.     In  contrast  to  another 
haptophore  wliich  the   amboceptor  possesses   and 
whicli   will   be  described   below,   that   one   which 
unites  with  the  cell  is  called  the  cytophilous  hapto- 
phore.    The  haptophore  of  the  erythrocyte  which 
enters  into  the  union  is  an  essential  part  of  a  re- 
ceptor of  the  red  cell,  consequently  we  say  that  the 
amboceptor  unites  with  a  receptor  of  the  corpuscle. 


of 

ceptor 


HEMOLYSINS.  261 

The  heating  of  serum  to  56°   C.  provides  one  y}^*^  Absorp- 

^  _  ^  tion   Experi- 

means   of   apparent   isolation   of   the   amboceptor  ment  in  the 
from  the  complement,  but  this  is  not  a  true  isola- 
tion in  that  complement  is  merely  rendered  inac- 
-tive  by  the  heat  rather  than  totally  eliminated. 

Ehrlich  and  Morgenroth  devised  a  method  by 
which  the  amboceptors  may  be  separated  from  a 
fresh  immune  serum  without  in  any  way  injuring 
the  complement.  This  is  accomplished  by  per- 
forming the  binding  experiment,  already  alluded 
to,  at  a  low  temperature.  The  serum,  containing 
both  amboceptors  and  complement,  is  cooled  to  0° 
C.  or  slightly  above,  by  means  of  a  freezing  mix- 
ture of  salt  and  ice.  A  suspension  of  the  homolo- 
gous corpuscles  is  cooled  to  the  same  point,  the 
serum  is  added  and  the  mixture  maintained  at  0° 
to  4°  C.  for  from  fifteen  to  twenty  minutes.  At  the 
end  of  this  time  the  sensitized  cells  are  removed 
by  immediate  centrifugation  at  a  low  temperature, 
and  are  washed  entirely  free  from  serum  by  the 
use  of  ice-cold  salt  solution.  If  the  low  tempera- 
ture has  been  adhered  to  rigorously  and  the  work 
done  quickly,  the  corpuscles  are  not  laked  during 
the  manipulations  in  spite  of  the  presence  of  both 
amboceptors  and  complement.  Furthermore,  the 
washed  sensitized  cells  remain  intact  even  when 
their  temperature  reaches  that  of  the  thermostat, 
whereas  if  some  fresh  normal  serum  or  the  serum 
from  which  the  amboceptors  were  absorbed  is 
added,  they  undergo  hemolysis  as  readily  as  when 
treated  with  the  active  immune  serum.  The 
original  immune  serum  is  now  a  solution  of  com- 
plement, and  fresh  corpuscles  which  are  added  to 
it  are  not  dissolved  because  of  the  absence  of  ambo- 
ceptors. 


262 


INFECTION     AND     IMMUNITY. 


tor. 


These  results  show  the  following  important 
facts:  Amboceptor  and  complement  exist  side  by 
side  in  an  immune  serum,  not  as  a  united  sub- 
stance. Union  of  amboceptor  with  cell  is  inde- 
pendent of  complement,  the  latter  being  taken  up 
only  after  the  amboceptor-cell  reaction  has  oc- 
curred. Amboceptors  unite  with  cells  at  a  low 
temperature,  whereas  complement  requires  a 
higher  temperature  for  its  union  and  for  the  fer- 
ment-like activity  by  which  it  dissolves  or  kills  the 
cells. 

Complement-       That    Constituent    of    the    amboceptor    which 
Hapt^phorl   unitcs  witli  the  cell  has  been  referred  to  as  the 

of  Ambocep-  cytophilous  liaptophorc.  Ehrlich  and  his  follow- 
ers believe  that  complement  in  establishing  con- 
nection with  the  cells  does  so  by  combining  with  a 
second  haptophore  of  the  amboceptor,  after  the 
latter  has  sensitized  the  erythrocyte  or  bacterium. 
Hence,  an  amboceptor  has,  as  the  name  implies, 
two  receiving  groups  or  haptophores,  the  second 
being  the  complementophilous  haptophore  (Fig. 
7).  It  is  hardly  desirable  to  discuss  various  ex- 
periments which  furnish  additional  evidence  of  the 
amboceptor  nature  of  the  thermostabile  body.  The 
observed  phenomena  allow  one  to  assign  to  it  the 
two  haptophores  mentioned. 

There  is  a  conflict  of  ideas  as  to  the  nature  of 
the  change  produced  by  the  amboceptors,  as  a  re- 
sult of  which  the  cells  are  made  susceptible  to  the 
action  of  complement.  Bordet  speaks  of  the  am- 
boceptor as  the  substance  sensibilisatrice,  the  sen- 
sitizing substance;  and  his  conception  of  the  ac- 
tion of  the  two  substances  he  has  compared  rough- 
ly to  the  opening  of  a  lock  for  which  two  keys  are 
demanded.     One  key,  amboceptor,  is  needed  to 


Action    of 
Amboceptors. 


MECHANISM     OF     HEMOLYSIS.  263 

prepare  the  lock  for  the  action  of  the  second  ke}^ 
complement,  the  latter  being  the  one  which  really 
opens  it. 

Metchnikoff  applies  the  name  fixator  to  the 
thermostabile  body,  having  in  mind  the  action  of 
a  mordant  in  preparing  tissues  or  other  substances 
for  the  reception  of  a  dye;  this  differs  little  from 
preparator,  the  word  used  by  Gruber. 

The  idea  of  Ehrlich,  however,  is  distinctly  at 
variance  with  the  conceptions  mentioned,  for  he 
sees  in  the  union  of  amboceptor  with  cell  nothing 
more  than  the  introduction  of  a  new  chemical 
affinity,  i.  e.,  one  which  attracts  complement,  and 
this  new  affinity  does  not  lie  in  the  cell  itself,  but 
rather  in  the  amboceptor  (complementophilous 
haptophore)  after  the  union  has  occurred.  Hence, 
the  terms  intermediary  body  (Zwisclienlcdrper) , 
copula  of  Miiller,  and  desmon  of  London,  are 
words  which  carry  with  them  the  meaning  that  the 
amboceptor  first  unites  with  the  cell  and  then  acts 
as  a  linking  substance  through  which  complement 
finally  is  put  in  relation  to  the  cell.  This  also  is 
the  meaning  embodied  in  the  amboceptor  of 
Ehrlich,  the  word  indicating  more  accurately  his 
conception  of  the  method  by  which  the  substance 
acts  as  an  intermediary  body. 

If  we  consider  it  established  that  in  the  process   structure  of 

«        ,    T       .  .  ,     ,  TIT     Complement. 

01  cytolysis  union  occurs  between  complement  and 
amboceptor  we  must  at  the  same  time  assign  a 
haptophorous  group  to  complement.  Union  would 
be  impossible  without  it.  Corroborative  proof  of 
the  existence  of  this  haptophore  lies  in  the  fact 
that  immunization  with  complement  results  in  the 
formation  of  anticomplement,  a  prerequisite  for 
which  is  union  of  complement  with  cell  receptors 


264  INFECTION     AND     IMMUNITY. 

in  the  immunized  animal ;  and  this  union,  it  seems 
necessar}^  to  assume,  takes  place  through  a  binding 
group.  The  mere  possession  of  a  haptophore,  how- 
ever, does  not  account  for  the  ferment-like  activity 
of  complement.  The  latter  characteristic  resides 
in  the  so-called  z3^motoxic  group;  hence,  comple- 
ment, having  a  binding  and  a  toxic  group,  has  a 
structure  like  that  of  a  toxin. 
compie-  Somewhat  loosely  we  have  said  that  the  inactiv- 
men  o  « .  [^y  ^f  ^  scrum  whicli  has  been  heated  to  56°  C. 
depends  on  destruction  of  the  complement.  This 
is  not  strictly  true,  however,  for  such  treatment 
destroys  only  the  zymotoxic  group,  the  haptophor- 
ous  constituent  remaining  uninjured.  Comple- 
ment altered  in  this  respect  is  called  complemen- 
toid,  and  it  is  analogous  to  toxoid,  agglutinoid  and 
precipitoid.  Two  essential  facts  go  to  show  that 
this  is  the  principle  change  wrought  by  heating. 
First,  the  fact  stated  above,  that  immunization 
with  complementoid,  causes  the  formation  of 
anticomplement.  Second,  complementoid  may 
exceed  true  complement  in  its  affinity  for  the 
amboceptor,  and  if  sensitized  cells  are  treated  with 
a  serum  containing  a  mixture  of  complement  and 
complementoid,  the  latter  may  occupy  completely 
the  complementophilous  haptophores  of  the  ambo- 
ceptors and  thus  may  block  the  way  for  action  on 
the  part  of  complement.  This  is  again  the  spe- 
cific inhibition  which  has  been  mentioned  in  con- 
nection with  toxoids,  agglutinoids  and  precipi- 
toids.  This  is  the  Complementoid-Verstopfung 
(complementoid  obstruction)  of  Ehrlich. 
Forniaiion  The  amboccptor,  as  the  characteristic  property 
of  Amboce^>-  q£  ^  bactcricidal  or  of  a  hemolytic  serum,  is  a  spe- 
cific product  of  the  immunization,   whereas  the 


FORMATION    OF    AMBOCEPTORS.  2Go 

amount  and  character  of  complement  in  the  im- 
munized animal  undergoes  little  or  no  change. 
We  are,  of  course,  obliged  to  consider  the  ambo- 
ceptors as  a  product  of  the  cells  of  the  body.  In 
the  terminology  of  Ehrlich,  they  are  discarded  cell 
receptors,  and  with  their  two  haptophores  repre- 
sent a  more  complex  structure  than  either  the  re- 


Fig.  7. — Graphic  representation  of  receptors  of  the  third 
order,  and  of  some  substance  uniting  with  one  of  them. 
Cj  Cell  receptor  the  third  order,  an  amboceptor  ;  e,  one  of  the 
haptophores  of  the  amboceptor,  with  which  some  food  sub- 
stance or  product  of  bacterial  disintegration,  f,  may  unite  ; 
g,  the  other  haptophore  of  the  amboceptor  with  which  com- 
plement may  unite  ;  E,  complement ;  Ji,  the  haptophore,  and 
Sj  the  zymotoxic  group  of  complement.  From  Ehrlich's 
"Schlussbetrachtungen,"  Nothnagel's  System  of  Medicine, 
vol.  viii. 

ceptors  of  antitoxin  or  agglutinin;  the  latter  are 
uniceptors;  the  former  amboceptors,  and  because 
of  their  higher  differentiation  Ehrlich  has  called 
them  receptors  of  the  third  order  (Fig.  7). 


266  INFECTION     AND     IMMUNITY. 

"When  micro-organisms  gain  entrance  to  the 
body  they  are  killed  and  dissolved  in  considerable 
masses.  As  a  result  of  the  solution,  certain  bac- 
terial constituents  reach  the  circulation,  and 
among  them  are  molecules  or  receptors  which  pos- 
sess haptophores  capable  of  uniting  with  a  par- 
ticular type  of  amboceptor,  the  latter  being  an  in- 
tegral part  of  some  tissue  cells.  This  union  hav- 
ing taken  place,  an  affinity  for  circulating  com- 
plement may  be  created  as  in  the  test-tube  experi- 
ments. We  have  thus  the  possibility  of  stimula- 
tion of  the  cell  by  the  bacterial  constituent  itself 
as  a  toxic  or  unusual  food  substance,  or  the  toxic 
action  may  be  caused  by  products  of  disintegra- 
tion of  the  bacterial  substance,  the  disintegration 
having  been  accomplished  by  the  digestive  action 
of  the  complement  which  was  taken  up  by  the  am- 
boceptor. The  effect  is  that  of  an  unusual  stimu- 
lation, in  response  to  which  the  cell,  if  not  fatally 
injured,  reproduces  many  amboceptors  correspond- 
ing to  the  type  which  was  occupied  or  injured. 
As  in  the  formation  of  other  antibodies,  the  new- 
formed  amboceptors  reach  the  general  fluids  of  the 
body. 
Specificity _  of  Conceming  the  specificity  of  serum-hemolysins 
Amboceptors  and  scrum-bacteriolj^sins  for  their  homologous 
^ent^"  cells,  we,  of  course,  refer  to  the  specificity  of  the 
whole  amboceptor-complement  complex.  It  is  nec- 
essary to  throw  the  responsibility  on  both  sub- 
stances, because  of  'the  variations  which  exist 
among  complements  as  well  as  among  ambocep- 
tors. Inasmuch,  however,  as  the  heat-resistant 
body  alone  is  increased  during  immunization  or 
infection,  the  greater  part  of  the  specificity  would 


BACTERIAL   RECEPTORS.  267 

seem  to  depend  on  the  nature  of  the  amboceptor 
rather  than  on  that  of  complement. 

All  bacteria  which  stimulate  to  the  formation  Bacterial 
of  bactericidal  serums  do  so  because  of  certain  re-  ^ceptors. 
ceptors  which  they  possess.  These  are,  of  course, 
analogous  to  the  receptors  of  er3^throcytes  which 
cause  the  production  of  the  hemolytic  bodies  in 
serum.  Bacteria  have,  in  addition,  many  other  re- 
ceptors, some  of  which  cause  the  development  of 
agglutinins.  In  the  latter  instance  we  speak  of  the 
agglutinogenic  receptors  of  the  cells,  but  there  is 
no  name  of  equal  convenience  which  is  used  to 
designate  the  receptors  which  stimulate  to  the 
formation  of  amboceptors.  No  two  micro-organ- 
isms contain  an  identical  receptor  apparatus;  if 
the  contrary  were  the  case  their  antiserums  would 
coincide  in  their  bactericidal  action.  Therefore,  the 
cell  receptors  (amboceptors)  with  which  they  unite 
during  immunization  differ  correspondingly  in 
their  cytophilous  haptophores.  The  cytophilous 
haptophore  of  the  typhoid  amboceptor  finds  its 
specific  counterpart  in  the  typhoid  bacillus,  and 
finding  no  such  counterpart  in  the  vibrio  of  chol- 
era, the  latter  can  not  be  sensitized  by  the  anti- 
typhoid serum ;  on  this  fact  depends  the  specificity 
of  the  serum.  This  conception  does  not  interfere 
with  the  explanation  of  the  group  reaction  among 
bactericidal  serums,  for  it  is  conceivable  that  the 
colon  bacillus,  for  example,  has,  in  addition  to 
those  receptors  which  characterize  the  organism,  a 
small  percentage  of  receptors  which  are  identical 
with  those  characterizing  the  tjrphoid  bacillus.  In 
accordance  with  this  possibility  an  antityphoid 
serum  may  well,  as  it  does,  show  some  increased 
bactericidal  power  for  closely  related  organisms. 


268  INFECTION     AND     IMMUNITY. 

Hence  the  explanation  of  group  bacteriol3^sis  is 
identical  with  that  of  group  agglutination. 
»initipiicity       Thcpc  is  a  wicle  difference  of  opinion  resrardinor 

of     Coinple-      1  .  »  ,  . 

ments.  the  unitj  of  Complement,  or  alexin,  its  synonym. 
Bordet  and  his  followers  stand  for  the  unity  of  the 
alexins,  and  their  position  rests  on  the  fact  that  a 
given  normal  serum  may  be  used  to  activate  many 
different  amboceptors.  We  should  appreciate  that 
this  phenomenon  might  depend  on  the  broad  range 
of  action  of  a  single  complement,  or  on  the  pres- 
ence of  different  complements  each  being  specific 
for  a  particular  amboceptor.  Ehrlich  and  his 
school  take  the  latter  view  and  have  actually  dem- 
onstrated a  multiplicity  of  complements  in  a  few 
instances.  Ehrlich  and  Sachs  treated  fresh  nor- 
mal serums  (complement)  in  various  ways,  such 
as  digestion  with  papain,  partial  destruction  with 
alkalies,  heat,  etc.,  and  were  able  by  these  methods 
to  destroy  the  complement  for  one  kind  of  ambo- 
ceptor, while  the  serum  still  retained  its  power  for 
activating  other  amboceptors.  Accordingly,  it 
seems  clear  that  the  ability  of  a  normal  serum  to 
activate  a  given  amboceptor  depends  not  only  on 
the  presence  of  complement  in  a  general  sense,  but 
on  the  presence  of  a  suitable  complement,  i.  e.,  one 
the  haptophore  of  which  corresponds  to  the  com- 
plementophilous  haptophore  of  the  amboceptor. 
This  point  is  of  great  importance  in  reference  to 
the  treatment  of  infectious  diseases  with  antibac- 
terial serums,  for  the  efficacy  of  the  serum  would 
seem  to  depend  on  the  introduction  of  suitable 
complement  in  conjunction  with  the  amboceptors, 
or  on  the  existence  of  such  complement  in  the  body 
of  the  patient. 


COMPLEMENT   AND  ANTICOMFLEMENT.    269 

Added  proof  of  the  multiplicity  of  complements 
has  been  obtained  by  experiments  with  anticom- 
plements.  As  stated,  the  latter  are  obtained  by 
immunization  of  suitable  animals  with  normal  or 
immune  senmis  which  contain  complement  or  com- 
plementoid.  When  they  are  mixed  with  the  homolo- 
gous complements  the  haptophores  of  the  latter 
are  bound  by  means  of  the  haptophores  of  the  anti- 
complements.  The  evidence  of  this  union  lies  in 
the  fact  that  a  complement  which  has  been  treated 
with  its  specific  anticomplement  is  no  longer  able 
to  activate  the  appropriate  amboceptor  (p.  280). 
With  properly  selected  serums,  it  may  be  shown 
that  a  given  anticomplement  will  neutralize  a  com- 
plement which  is  specific  for  one  amboceptor,  but 
will  have  no  effect  on  another  complement  which 
activates  a  different  amboceptor.  Hence,  comple- 
ments differ  at  least  in  this  respect  that  not  all  have 
identical  haptophores.  Immunization  with  leuco- 
cytes, cells  which  contain  complement,  also  causes 
the  formation  of  anticomplement.  Both  natural 
and  acquired  antibacterial  immunity  may  be  low- 
ered by  the  injection  of  anticomplement  which  is 
homologous  to  the  complement  of  the  animal. 

Some  time  ago,  Ehrlich  expressed  the  opinion 
that  an  amboceptor  in  certain  cases  may  have  more 
than  one  complementophilous  haptophore;  in 
other  words,  that  it  may  be  a  polyceptor  rather 
than  an  amboceptor.  This  has  again  been  empha- 
sized recently  by  way  of  explaining  the  ability  of 
an  amboceptor  to  absorb  from  a  normal  serum  not 
only  the  complement  which  serves  to  activate  the 
amboceptor,  but  also  others  which  happen  to  be 
present  in  the  serum.  The  former  is  spoken  of  as 
tlie  dominant  complement  and  the  latter  as  non- 


Anticom- 
pleinents. 


270 


INFECTION     AND     IMMUNITY. 


dominant  complements.     Figure  8  is  an  illustra- 
tion of  such  a  polyceptor. 
Antiambo-       If  ouG  immunizGS  with  an  immune  serum  the 
product  is  spoken  of  in  a  general  way  as  an  anti- 


Pig^  8. — Illustrating  the  amboceptor  with  more  than  one 
complementophilous  haptophore  (a  polyceptor).  a.  Cell  re- 
ceptor ;  b,  cytophil«4us  haptophore  of  the  amboceptor ;  c,  the 
dominant  compleiuent ;  d,  the  non-dominant  complements ; 
,  the  heptophore  of  the  amboceptor  for  the  dominant  com- 
plement;/8,  those  for  the  non-dominant  complements.  (From 
Ehrlich  and  Marshall.) 

immune  serum.  The  latter  contains,  as  stated, 
anticomplement,  and  through  the  agency  of  this 
substance  the  antiserum  antagonizes  the  action  of 
the  serum  which  was  used  for  the  immunization. 


ANTIAMBOCEPTOKS.  271 

Inasmuch,  however,  as  the  immune  serum  contains 
amboceptors  also,  the  antagonistic  action  of  the 
antiserum  may  depend,  in  part,  on  the  presence  of 
antiamboceptors.  DitTerentiation  between  the  ac- 
tion of  anticomplement  and  antiamboceptor  is  dif- 
ficult, but  it  may  be  accomplished  in  certain  cases 
by  appropriate  binding  experiments.  Serum  1,  an 
inactive  hemolytic  serum,  i.  e.,  a  solution  of  ambo- 
ceptors and  complem^entoid,  is  treated  with  serum 
2.  Serum  2  has  been  obtained  by  immunization  of 
an  animal  with  serum  1,  and  contains  anticomple- 
ment and  possibly  antiamboceptors.  If  serum  2 
contains  only  anticomplement,  it  will  have  no  ef- 
fect on  the  amboceptors  of  serum  1,  when  the  two 
are  mixed.  The  amboceptors  are  free  to  sensitize 
corpuscles  which  may  be  added,  and  the  latter  when 
sensitized  undergo  hemolysis  in  the  presence  of 
complement.  If,  however,  serum  2  contains  anti- 
amboceptors, either  the  cytophilous  or  the  comple- 
mentophilous  haptophore  of  the  amboceptor  will 
be  bound.  In  either  case,  corpuscles  which  are 
added  subsequently  would  not  appear  as  sensitized, 
for  if  the  cytophilous  haptophore  had  been  bound 
by  antiamboceptor  union  between  cell  receptor  and 
amboceptor  could  not  occur;  and  if  the  comple- 
mentophilous  haptophore  had  been  preoccupied 
complement  would  have  no  effect  even  if  the  ambo- 
ceptors had  united  with  the  cells  by  their  unbound 
cytophilous  haptophores.  Ehrlich  and  Morgenroth 
demonstrated  such  antiamboceptors  for  certain 
hemolytic  serums,  and  it  was  their  belief  that  they 
combine  with  the  cytophilous  rather  than  with  the 
complementophilous  haptophore  of  the  ambo- 
ceptor. However,  Ehrlich  has  recently  been  able 
to  prove  the  occurrence  of  an  antibody  for  the  com- 


272 


INFECTION     AND     IMMUNITY. 


Danger^  of  plementophilous  haptophore  in  one  case.     Pfeiffer 
of**Ar?tia\n"  also  repoits  the  demonstration  of  antiamboceptors 
boceptor.   £q^  ^Yyq  specific  amboccptors  of  anticholera  sernm. 
The  possibility  of  antianiboceptor  formation  is  one 
of  practical  bearing,  in  view  of  the  fact  that  the 
prolonged  treatment  of  a  patient  with  a  bacteri- 
cidal serum  may  result  in  the  development  of  snch 
antibodies.     If  present  in  sufficient  amount  they 
would  combine  with  new  amboceptors  which  were 
injected  and  thus  deviate  the  latter  from  the  bac- 
teria. 
Deviation       A  pheuoinenou  equally  of  theoretical  and  prac- 

of    Coiuple-       ,      ,    :  1  J        T  -11     XI  11     T    T       • 

meiit   and  tical  importance  has  to  do  with  the  so-calJed  devia- 

icai   Dan-  tiou    (AhJenlning)    of  complement.     It  has  been 

^^*''   found  that  the  action  of  a  bactericidal  or  hemol}dic 


"^^^^ii^il-^ 


Fig.  9. — Illustrating  deviation  of  complement.  The  free 
amboceptors  have  combined  with  the  available  complement, 
and  thereby  prevented  the  latter  from  activating  the  am- 
boceptors which  have  united  with  the  bacterial  cell.  (From 
Neisser  and  Wechsberg.) 

serum  is  lessened,  if  a  great  excess  of  amboceptors 
over  complement  is  added.  To  explain  this  fact 
Neisser  and  Wechsberg  have  .supposed  that  when 
so  many  amboceptors  are  present  that  all  can  not 
be  taken  up  by  the  cells,  those  which  remain  free 
are  able  to  combine  with  some  of  the  complement 
which  is  present  and  thus  prevent  the  accession  of 
the  latter  to  the  sensitized  cells;  that  is  to  say,  the 
complement  is  diverted  from  its  natural  direction 
of  activity   (Fig.  9).     This  amounts  to  a  protec- 


VENOM   HEMOLYSIS.  273 

tion  of  the  sensitized  cells  from  the  action  of  the 
complement.  The  phenomenon  led  Wechsberg  to 
suggest  that  in  the  therapeutic  administration  of 
bactericidal  serums  it  may  be  possible  to  give  too 
much  of  the  serum.  Although  diversion  of  com- 
plement is  a  demonstrated  fact,  its  importance  in 
serum  therapy  is  perhaps  not  definitely  settled. 

It  is  of  interest  that  amboceptors  are  widely  dis-  Hemolytic 
tributed  in  the  animal  kingdom^  and  that  in  cer-  o?Veno?u.**^** 
tain  instances  they  may  be  demonstrated  in  the 
secretions.  It  has  long  been  known  that  the 
venoms  of  many  serpents  have  the  ^Dower  of  des- 
troying red  blood  cells.  A  given  venom  may 
contain  several  toxic  substances,  and  the  poisons 
of  different  serpents  by  no  means  coincide  in  their  . 
toxic  properties.  Cobra  venom  contains  two  well- 
known  toxins,  one  for  the  nervous  tissue  and  one 
which  dissolves  erythrocytes,  the  neurotoxin  having 
the  greater  pathogenic  significance.  Cobra  venom 
also  agglutinates  red  blood  corpuscles,  and  Flexner 
and  Xoguchi  found  that  it  contains  special  toxins 
for  the  cells  of  various  organs  (cytotoxins).  The 
venom  of  the  rattlesnake,  on  the  other  hand,  is 
neurotoxic  to  a  less  degree,  but  has  a  pronounced 
influence  in  causing  capillary  hemorrhages.  The 
latter  power  Flexner  ascribes  to  a  toxin  for 
endothelial  cells,  which  he  calls  hemorrhagin. 
Through  the  works  both  of  Flexner  and  Noguchi 
and  of  Ivyes,  facts  were  learned  concerning  the 
hemolytic  toxin  of  cobra  venom,  which  may  be  ot 
great  importance  in  problems  of  general  immun- 
ity. It  seems  that  the  hemolysin  of  venom  is  an 
amboceptor  rather  tnan  a  toxin  of  the  usual 
nature,  and  that  rne  aid  of  complement  is  neces- 


274 


INFECTION     AND    IMMUNITY. 


Endocom- 
pleinent. 


LiCcitliin 
Activation 


sary  for  its  toxic  action.  The  venom  itself  con- 
tains only  the  amboceptors,  hence  the  toxicity  of 
the  substance  depends  on  its  being  complemented 
after  it  is  introduced  into  the  body.  The  posses- 
sion of  suitable  complement,  therefore,  is  a  source 
of  danger  in  this  instance  rather  than  a  means  of 
protection  for  the  individual.  One  may  very  well 
suspect  that  a  similar  relationship  is  possible  in 
connection  with  other  substances  which  are  as  yet 
unknown. 

A  fact  of  additional  importance  is  that  the  am- 
boceptor finds  suitable  complement  not  only  in  the 
serum  of  the  animal  but  it  may  also  be  activated 
by  a  complement  which  the  erythrocytes  them- 
selves contain.  Kyes  speaks  of  the  latter  as  endo- 
complement,  i.  e.,  endocellular  complement. 

In  attempting  to  discover  the  nature  of  the  com- 
plement which  is  present  in  the  erythrocytes,  vari- 
ous substances  existing  normally  in  the  red  cells, 
as  cholesterin  and  lecithin,  were  obtained  in  pure 
form  and  their  activating  power  for  the  cobra  am- 
boceptors was  tested  in  reagent-glass  experiments. 
From  this  work  it  was  learned  that  lecithin,  a  defi- 
nitely known  chemical  substance,  has  the  activat- 
ing power,  and  it  was,  therefore,  assumed  that  the 
endocomplement  of  erythrocytes  is  nothing  more 
or  less  than  lecithin.  All  erythrocytes  contain 
lecithin,  yet  not  all  are  equally  susceptible  to  the 
action  of  venom  in  the  absence  of  serum  comple- 
ment ;  that  is  to  say,  endocellular  lecithin  does  not 
act  as  complement  with  equal  readiness  in  all 
cases.  In  order  to  explain  this  variation  it  was 
necessary  to  assume  that  the  lecithin  in  the  cells 
of  one  animal  may  be  more  available  as  comple- 
ment because  it  is  bound  to  other  cell  constituents 


COBRA-LECITHID.  275 

only  in  a  very  loose  way,  whereas  in  more  resistant 
cells  the  union  is  of  a  firmer  nature. 

The  relationship  between  cobra  amboceptors  and 
lecithin  seems  to  be  a  very  definite  one,  for  Kyes 
was  able  to  obtain  a  union  of  the  two  without  the 
intervention  of  erythrocytes.  The  resulting  sub- 
stance, the  cobra-lecithid  of  Kyes,  is  a  completed 
toxin  and  needs  no  further  activation.  We  have 
yet  to  learn  of  the  true  nature  of  this  new  com- 
pound, the  discovery  of  which  seemed  to  augur  a 
more  intimate  chemical  Imowledge  of  the  sub- 
stances which  are  concerned  in  immunity. 

According  to  Bang  lecithin  itself  has  no  activat- 
ing power  for  snake  venoms.  He  attributes  the 
hemolytic  action  of  the  product  of  the  action  of 
lecithin  on  venom  according  to  the  Kyes  technic 
as  due  to  pre-existant  impurities  in  the  lecithin 
That  hemolytic  substances  exist  in  unpurified 
lecithin  there  is  no  doubt.  The  lecithin  used  by 
Kyes  in  his  experiments,  however,  was  prepared 
with  great  precaution  to  avoid  the  presence  of 
such  substances. 

V.  Dungern  and  Coca  attribute  the  action  of 
lecithin  or  venom  to  a  splitting  ofE  of  hemolytic 
products  from  the  lecithin  and  fail  to  obtain  an 
"antilecithid"  by  immunization.  They  also  point 
to  a  similarity  between  Kyes  elementary  analysis 
of  the  lecithid  and  that  of  lecithin  and  confirm  his 
analysis.    Their  view  is  supported  by  Manwaring. 

Kyes,  however,  had  pointed  out  the  fact  that 
elementary  analysis  is,  as  a  general  rule,  insuffi- 
cient to  determine  differences  in  substances  con- 
cerned in  immime  reactions  and  by  a  determina- 
tion of  molecular  weights  shows  that  cobra  lecithid 


Cobra-leci- 
thid 


276  INFECTION     AND     IMMUNITY. 

has  a  much  larger  molecule  than  lecithin  itself. 
His  immunization  of  animals  to  produce  an  anti- 
lecithid  extended  over  a  much  larger  period  than 
those  of  V.  Dungern  and  Coea. 
iientoiysis        Lecithin  is  a  colloid,  and  in  this  connection  it  is 

hy   tlie    Com-  .  ,      n      ,    •  i  t    •  i  • 

billed  Ac-  interesting  to  note  that  it  may  be  used  m  combma- 
''loids".  tion  with  still  another  colloid  in  such  manner  that 
the  hemolysis  which  they  cause  is  analogous  to 
that  produced  by  hemolytic  amboceptors  and  com- 
plements. Landsteiner  tried  the  effect  of  col- 
loidal silicic  acid  on  erythrocytes  Avhich  were  en- 
tirely freed  from  serum^  with  the  result  that  the 
corpuscles  were  agglutinated  under  its  influence. 
It  developed  further,  however,  that  colloidal  silicic 
acid  not  only  acts  as  an  agglutinin,  but  also  simu- 
lates a  hemol3^tic  amboceptor,  and  in  the  latter 
capacity  it  may  be  activated  either  by  the  ordinary 
complement  of  serum  or  by  lecithin.  Hence,  we 
have  here  an  instance  of  the  entire  cytolytic  action 
being  performed  by  two  known  chemicals,  which 
in  their  action  appear  to  be  analogous  to  ambocep- 
tors and  complements.  Yet  even  the  action  of 
these  substances  is  obscure,  for  although  the  chem- 
ical formulae  of  silicic  acid  and  lecithin  are  suffi- 
ciently well  known,  the  explanation  of  their  activ- 
ity as  colloids  is  equally  obscure  with  that  of  the 
albuminous  substances. 
zveiitraiiza-  Auotlicr  discovery  Avhich  tends  to  bring  the 
piement  by  immuue  suljstanccs  into  closer  toucli  with  ]iure 
chemistry  is  that  of  Hektoen  concerning  the  abil- 
ity of  certain  salts  (calcium  chlorid,  barium 
chlorid,  etc.),  to  combine  with  complement  in 
such  a  way  that  the  latter  loses  its  activating  and 
combining  function  in  relation  to  amboceptors. 
This  was  mentioned  incidentallv  under  the  sub- 


Salt. 


-NATURE    OF    COMPLEMENT.  277 

ject  of  antitoxins.  The  activity  of  the  comple- 
ment is  again  restored  if  the  inhibiting  salts  are 
precipitated  by  suitable  chemicals.  The  salts  are 
used  in  such  dilutions  that  they  are  largely  ionized, 
and  Manwaring  believes  their  inhibiting  action  is 
due  to  the  formation  of  compounds  of  the  posi- 
tive ions  with  the  complement,  resulting  in  such 
substances  as  Ca-complement,  Ba-complement, 
etc.  ^^^en  the  precipitating  chemicals  are  added 
the  ions  are  freed  from  this  combination,  as  a  re- 
sult of  which  the  complement  recovers  its  activat- 
ing properties.  It  has  not  as  yet  been  determined 
whether  variations  in  the  salts  in  the  fluids  of  the 
body  cause  changes  in  resistance  by  their  action  on 
native  complements. 

The  work  of  Ferrata,  Hans  Sachs  and  Teruuchi,   Further  An- 
Brand   and   Hecker   has   shown   that  complement   complement. 
may  be  divided  into  two  parts  by  the  separation  of 
the  albumin  and  globulin  contents  of  the  serum 
containing  it. 

Xeither  of  these  two  parts  alone  has  the  power 
to  bring  about  hemolysis  in  corpuscles  previously 
sensitized  by  the  addition  of  amboceptor.  When 
combined,  however,  hemolysis  takes  place  as  before 
separation. 

Absorption  of  the  globulin  fraction  takes  place 
when  it  is  added  to  sensitized  corpuscles,  result- 
ing in  "Persensitized  corpuscles'^  (Michaelis  and 
Skwirsky),  which  then  undergo  hemolysis  on  ad- 
dition of  the  albumin  fraction.  The  albumin 
fraction,  on  the  contrary,  is  incapable  of  being 
bound  by  the  sensitized  corpuscles  in  the  absence 
of  the  globulin  fraction.  Brand  therefore  terms 
the  globulin  fraction  as  complement  "middlepiece" 


278  INFECTION     AND     IMMUNITY. 

and  designates  the  albumin  fraction  as  comple- 
ment ^^end-piece." 

The  end-piece^  middle-piece  and  amboceptor 
bear  the  same  relation  to  each  other  as  whole 
complement  amboceptor  and  antigen. 

The  middle-piece  is  thermostabile  when  attached 
to  the  amboceptor  antigen  complex,  but  thermo- 
labile  when  heated  alone  or  in  combination  with 
the  end-piece.  The  end-piece  is  thermolabile.  In 
specific  complement  deviation,  it  is  the  middle- 
piece  which  becomes  bound,  the  end-piece  remain- 
ing free. 

Attempts  to  ascertain  the  nature  of  these  two 
parts  by  substitution  of  lecithin  and  other  lipoids 
have  so  far  been  without  result  in  explaining  the 
nature  of  the  two  components  (Lief man  and 
Cohn). 


CHAPTER  XVII 


COMPLEMENT    DEVIATION". 

In  1901,  Bordet  and  Gengou  observed  that  when 
an  antigen  was  mixed  with  its  specific  antibody  in 
the  presence  of  complement,  the  complement  was 
fixed  or  bound  and  thus  rendered  unavailable  for 
further  reactions.  This  phenomenon  has  since  be- 
come widely  known  as  complement  deviation,  com- 
plement binding,  or  complement  fixation;  and  the 
principle  underlying  it  has  become  of  extreme 
value  in  the  determination  of  the  presence  of 
substances  whoso  interaction  is  followed  by  no 
readily  perceptible  result  such  as  lysis  or  precipi- 
tation. 

It  will  be  seen  that  such  a  reaction  is  analogous 
to  certain  chemical  reactions  such  as  the  combina- 
tion of  ordinary  acids  and  alkalies  in  which  the 
presence  of  the  reaction  is  determined  by  the  use 
of  indicators  such  as  litmus  or  phenolphthalein. 
Bordet  and  Gengou  used  as  an  indicator  a  hem- 
olytic system  of  erythrocytes  with  their  specific 
amboceptor.  In  this  way,  for  instance,  by  mixing 
typhoid  bacilli  with  antityphoid  serum,  incubating 
for  a  time  and  then  adding  erythroc3^tes  sensitized 
with  their  inactivated  antiserum,  it  was  observed 
that  hemolysis  did  not  take  place.  The  comple- 
ment in  the  antityphoid  serum  had  been  fixed  to 
the  typhoid  bacilli  by  the  t3^phoid  antibody  and 
was  thus  rendered  unavailable  for  the  hemolysis 
of  the  sensitized  erythrocj'tes,  subsequently  added. 
Bordet  also  showed  that  other  indicators  such  as 


280  INFECTION     AND     IMMUNITY. 

a  bacteriolytic  S3^stem  could  be  used  instead  of 
hemolysis,  in  order  to  test  for  the  binding  of 
complement. 
Non-si>ecific  ComiDlcment  deviation  obviously  belongs  to  a 
luiiibition.  large  group  01  complement  inhibition  phenomena 
and  since  some  of  these  have  a  very  close  bearing 
on  the  complement  deviation  by  means  of  antigen- 
antibody  complex  it  is  well  to  review  them. 

Ehrlich  and  Morgenroth  made  use  of  the  com- 
plement inhibition  of  lowered  temperature  to 
separate  complement  from  amboceptor. 

Hektoen  and  Euediger  found  that  various  ions 
might  render  complement  inactive.  Certain  sub- 
stances which  in  themselves  are  hemolytic  have 
been  shown  to  antagonize  complement  action. 
Among  these  are  to  be  mentioned  bile  salts,  salts 
of  fatty  acids,  lecithin  cholesterin  and  other  lipoid 
bodies. 

Suspensions  of  finely  divided  substances  have 
been  demonstrated  to  inhibit  complement  action 
and  the  assumption  that  their  ability  to  antagonize 
complement  is  due  to  their  adsorptive  property  is 
highly  probable.  Kaolin,  chalk,  carbon,  sand,  etc., 
have  been  used  in  this  way. 

A  wide  variety  of  colloidal  substances  have  been 
shown  to  inhibit  complement;  examples  of  these 
are  gelatin,  peptone,  aleuronat,  albumoses,  etc. 
Lastly,  extracts  of  bacteria,  normal  and  pathologic 
tissue  extracts  and  the  body  juices  work  as  com- 
plement inhibitors. 
Anticom-       Ehrlich    and    Bordet    by    immunizing    animals 

plenientN         .,,  ,  -i^    t    •  -\       • 

of  Ehrlich  With  normal  serum  succeeded  m  producing  serums 
and  Bordet.  j^gj^iy  antagonistic  to  complement  action.   Accord- 
ing to  the  Ehrlich  conception,  these  bodies  are  to 


INHIBITION    OF    COMPLEMENT.  281 

be  regarded  as  distinct  antibodies,  receptors  of 
the  first  order.  Moreschi,  however,  has  thrown 
doubt  on  the  existence  of  such  distinct  antibodies 
for  the  reason  that  in  using  normal  serum  as  com- 
plement a  mixture  of  protein  substances  is  used 
giving  rise^  in  immunization,  to  antialbuminous 
bodies  which  react  with  the  antigen  to  form  com- 
binations which  inhibit  or  bind  complement.  Such 
combinations  in  the  form  of  precipitates  may  be 
demonstrated  to  act  as  anticomplements.  The 
existence  of  true  anticomplements,  therefore, 
while  not  disproved,  has  not  been  satisfactorily 
demonstrated. 

The  presence  of  complementoid  in  inactivated 
serum  may  also  act  as  a  cause  of  complement  in- 
hibition by  occupying  the  receptors  of  the  anti- 
body. When  these  various  factors  which  com- 
plicate the  complement  filiation  reaction  are  con- 
sidered, it  will  be  seen  that  great  care  must  be 
taken  in  both  the  technic  and  the  interpretation  of 
results. 

The   substance   concerned  in  antigen,  antibody  Nature  of 

„       , .  •  1  ,     •        T     1  "p    Complement 

complement  fixation  is  obtained  by  processes  oi  Deviation 
immunization  similar  to  those  concerned  in  other 
antibodies.  In  the  one  case  the  reaction  is  fol- 
lowed by  perceptible  results,  in  the  other  by 
fixation  of  complement.  The  question  arises :  are 
the  antibodies  in  these  tAvo  kinds  of  reaction  iden- 
tical or  not? 

That  the  complement  fixation  antibody  is  dis- 
tinct from  precipitins  and  agglutinins  is  indi- 
cated in  different  ways.  Muir  and  Martin,  by 
immunizing  rabbits  with  guinea-pig  serum,  ob- 
tained an  antibody  capable  of  complement  fixation 


282  INFECTION     AND     IMMUNITY. 

but  which  contained  no  precipitin.  Moreschi  pro- 
duced in  fowls  antiserum  which  was  high  in 
precipitin  concentration  but  did  not  produce  com- 
plement fixation.  In  like  manner  the  presence  of 
antibody  complement  deviation  in  the  absence  of 
agglutinating  properties  has  been  noted.  In  gen- 
eral, complement  deviation  antibod}^  is  destroyed 
at  higher  temperatures  than  agglutinins. 

It  is  in  lytic  amboceptors  that  complement  fixa- 
tion antibody  has  its  closest  analogy  and  opinions 
are  divided  as  to  the  identity  of  the  two.  Neufeld 
and  Haendel  regard  amboceptor  and  complement 
fixation  antibody  as  distinct  from  each  other  and 
apply  the  name  "Bordet's  antibody'^  to  the  latter. 
They  reach  this  conclusion  from  the  fact  that  if 
cholera  bacilli  and  their  antiserum  are  mixed  with 
complement  and  allowed  to  act  at  0°  C,  hemolytic 
complement  is  absorbed  but  not  that  necessary  for 
bacteriolysis.  The  same  mixture  allowed  to  act  at 
37°  C.  results  in  an  inhibition  of  action  of  both 
complements.  The  objection  to  such  a  proof  lies 
in  the  fact  that  the  difference  may  be  due  to  a 
difference  in  the  complements  according  to  Ehrlich 
and  his  school,  who  believe  in  the  multiplicity  of 
complements.  Neufeld  and  Haendel  have  also 
immunized  animals  with  a  certain  water  vibrio 
and  obtained  a  serum  which  was  bacteriolytic 
against  this  vibrio,  but  not  against  cholera  vibrios. 
Complement  deviation,  on  the  other  hand,  was 
effected  by  using  either  of  the  two  micro-organisms 
as  antigen. 

If  Ehrlich's  definition  of  amboceptor  as  a  sub- 
stance which  unites  antigen  with  complement  is 
accepted,  it  is  apparent  that  the  term  will  apply 


VALUATION  OF  COMPLEMENT  DEVIATION       283 


to  "Bordet's  antibody/'  whether  it  is  identical 
with  other  amboceptors  or  not. 

It  will  be  readily  seen  that  the  reaction  of  com- 
plement fixation  like  other  immune  reactions  be- 
tween antigen  and  antibody  may  be  used  for  the 
identification  of  either  of  the  two  bodies  concerned. 

The  complement  fixation  test  has  been  used 
especially  by  Neisser  and  Sachs  similarly  to  the 
precipitin  test  for  the  differentiation  of  proteins. 

Animals  are  immunized  to  a  certain  protein 
and  an  antiserum  is  thus  obtained.  A  titration  is 
then  made  with  known  homologous  antigen  and 
antibody,  in  varying  quantities,  to  determine  the 
amount  of  antiserum  necessary  to  produce  com- 
plement deviation.  The  quantity  of  antiserum 
found  by  titration  to  be  necessary  for  complement 
fixation  in  the  presence  of  homologous  antigen,  is 
then  added  to  the  serum  or  protein  to  be  tested. 
If  this  protein  and  the  antiserum  are  homologous, 
a  complement  fixation  will  result.  The  method 
has  been  criticized  because  of  its  extreme  delicacy. 
It  is  estimated  that  amounts  of  protein  substances 
will  give  a  complement  fixation  test  which  are 
present  in  one-millionth  the  quantity  required  for 
a  precipitin  test.  Uhlenhuth  advises  the  control 
of  the  method  by  the  precipitin  test.  Although 
other  antigens  such  as  bacteria  may  be  identified 
by  complement  fixation,  the  existence  of  easier 
methods  makes  complement  fixation  of  little  value. 

The  existence  of  easier  methods  of  diagnosis 
results  in  infrequent  use  being  made  of  the  com- 
plement deviation  reaction  as  a  means  of  diagnosis 
in  infections  with  organisms  capable  of  cultiva- 
tion.     The    presence    of    the    reaction    has    been 


Practical 
Use  of  the 
Reaction. 


Biolog^ic  Test. 


As   Antil>od: 
Test. 


284  INFECTION     AND     IMMUNITY. 

demonstrated,  however,  in  a  large  number  of  in- 
fections— typhoid,  parat3^phoid,  streptococcus  in- 
fections (including  strei^tococcTls  infections  of 
scarlet  fever),  pneumonia,  dysentery,  diphtheria, 
etc. 

Kolle  and  Wassermann  have  demonstrated  com- 
plement fixation  in  meningitis  and  suggest  the  use 
of  the  reaction  to  determine  the  strength  of  men- 
ingococcus antiserum. 

Eegarding  the  presence  of  antitul)erculin  in  the 
blood  of  tuberculous  animals  and  man,  conflicting 
results  are  reported.  It  would  appear  that  com- 
plement fixation  reaction  is  inconstant  during  the 
course  of  tulDcrculosis  and  that  the  reaction  occurs 
more  constantly  after  the  use  of  therapeutic  in- 
oculations of  tuberculin  and  especially  of  emul- 
sions of  tubercle  bacilli. 
Complement       It  occurrcd  to  Wasscmiann  that  by  using  ex- 

Deviation     ,,»,•  j_    •     •  i-  i  i 

in  SFphiiis.  tracts  01  tissucs  Containing  antigen,  complement 
deviation  antibodies  might  be  found  in  infections 
in  which  the  antigen  could  not  be  cultivated.  By 
the  use  of  syphilitic  tissues  he  immunized  apes 
against  syphilis  and  by  using  such  syphilitic  tissues 
as  antigen  found  complement  deviation  antibodies 
in  the  serum  of  the  immunized  apes. 

Wassermann,  Neisser  and  Bruck,  in  1906,  pub- 
lished the  results  of  these  experiments  together 
with  a  method  adapting  them  to  the  serodiagnosis 
of  syphilis  which  has  become  commonly  known  as 
the  Wassermann  reaction.  Since  the  spirochetes 
of  syphilis  were  known  to  be  found  in  extreme 
numbers  in  the  liver  of  the  syphilitic  fetus,  an 
aqueous  extract  of  this  organ  was  used  as  antigen. 
To  this  extract  was  added  the  inactivated  serum 


inann. 


WA88ERMANN    REACTION.  285 

of  the  suspected  case  and  after  the  addition  of 
complement,  the  mixture  was  incubated  an  hour. 
Sheep's  corpuscles  with  specific  amboceptor  were 
then  added  and  the  mixture  again  incubated.  In 
case  the  syphilitic  antibody  was  present,  comple- 
ment became  bound  and  no  hemolysis  took  place 
upon  second  incubation.  Through  a  large  number 
of  tests  the  Wassermann  reaction  has  been  proved 
to  be  characteristic  for  syphilis. 

The  idea  of  Wassermann  that  the  complement  xature  of 
binding  was  due  to  extract  of  spirochetes  as  anti-  o£^wa"seVt" 
gen  and  specific  amboceptor,  soon  found  opposi- 
tion. Landsteiner,  Mliller  and  Poetzl,  Levaditi 
and  others  showed  by  the  use  of  alcoholic  extracts 
of  normal  organs  that  a  substance  could  be  ob- 
tained which  acted  as  antigen  and  could  be 
substituted  for  the  extract  of  syphilitic  liver  with- 
out changing  the  results  of  the  reaction.  Finally 
it  has  been  shown  that  mixtures  of  lipoid  sub- 
stances or  crude  tissue  lecithin  could  be  used  as 
antigen.  Wassermann  pointed  out  that  whereas 
his  aqueous  extract  of  syphilitic  tissues  was  ther- 
molabile  at  boiling,  the  alcoholic  extract  of  normal 
organs  was  thermostabile :  further  that  the  aqueous 
extracts  of  normal  organs  do  not  act  as  substitutes 
for  aqueous  extracts  of  syphilitic  organs.  He 
therefore  regarded  his  original  ideas  as  to  the 
specificity  of  antigen  as  correct  and  held  that 
aqueous  extract  of  syphilitic  liver  was  the  only 
extract  which  could  be  used  without  chance  for 
error. 

Seligmann  and  Pinkus  have  made  a  study  of 
the  various  extracts  and  conclude  that  the  differ- 
ence in  heating  aqueous  and  alcoholic  extracts  is 


286  INFECTION     AND     IMMUNITY. 

due  to  the  fact  that  in  the  aqueous  extracts,  a 
large  amount  of  protein  is  present  with  the  lipoids 
on  which  the  antigenic  action  depends,  and  that 
these  lipoids  become  bound  to  the  protein  through 
heating;  further,  they  believe  that  these  lipoid 
substances  may  be  extracted  with  water  in  syph- 
ilitic liver  because  through  degenerative  processes 
they  become  split  off,  while  in  normal  organs  they 
must  be  split  off  by  alcohol  and  heat. 

They  conclude  that  the  antigen  is  therefore  of 
non-specific  lipoid  nature  and  that  it  acts  as 
activating  the  complement  binding  property  of 
syphilitic  serum. 

The  nature  of  the  substance  in  the  serum  of 
s^^philitics  which  in  combination  with  antigen 
inhibits  complement  action,  is  still  unknown. 
Noguchi  has  shown  that  it  begins  to  show  the 
effects  of  heat  at  45°  C.  xA.t  56''  C.  it  is  somewhat 
diminished  in  activity  and  at  62°  C,  its  activity 
is  lost.  It  has  been  thought  of  as  an  antibody 
because  of  its  development  with  the  development 
of  the  disease  and  its  disappearance  with  the  cure 
by  specific  treatment. 
Technic.  As  was  stated  in  the  beginning  of  the  chapter, 
the  various  materials  used  in  complement  devia- 
tion may  of  themselves  have  anticomplementary 
properties.  In  addition,  it  might  be  stated  that 
extracts  of  organs  ma}^  also  have  a  hemolytic 
action.  The  importance  of  quantitative  relations 
and  contral  experiments  will  therefore  be  appar- 
ent. The  Noguchi  modification  of  Wassermann's 
method  has  given  satisfactory  results  in  a  large 
number  of  cases.     The  preparation  of  materials 


TECHNIC  OF  WASSERMANN  REACTION.     287 

required  for  the  test  will  be  described  and  then 
their  application  to  the  test. 

Sheep's  corpuscles  may  be  obtained  from  the 
jugular  vein  of  the  animal.  The  blood  is  defibri- 
nated  and  washed  by  centrifugation  with  salt 
solution,  the  salt  solution  being  changed  twice. 
A  5  per  cent,  suspension  of  these  corpuscles  in 
0.85  per  cent,  salt  solution  is  used  for  the  test. 

Inactivated  hemolytic  serum  for  sheep's  cor- 
puscles is  prepared  by  immunizing  a  rabbit  against 
sheep's  corpuscles.  The  animals  should  be  injected 
intraperitoneally  with  washed  corpuscles  made  up 
to  the  volume  of  blood  from  which  they  were 
taken,  by  the  addition  of  salt  solution.  At  least 
four  or  five  injections  should  be  given  at  intervals 
of  from  four  days  to  a  week,  and  with  amounts 
beginning  with  2  c.c.  and  ending  with  from  12  to 
20  c.c.  The  animal  should  not  be  bled  before  ten 
days  after  the  last  injection.  Blood  is  obtained 
from  the  marginal  vein  of  the  ear  and  allowed  to 
clot.  The  serum  is  then  removed,  heated  to  56° 
C.  for  one-half  hour  and  standardized  as  follows: 
Varying  graded  amounts  of  the  inactivated  serum 
plus  0.1  c.c.  of  complement  (fresh  guinea-pig 
sermii,  best  obtained  by  aspiration  from  the  heart), 
are  added  to  each  of  a  number  of  tubes  containing 
1  c.c.  of  5  per  cent,  sheep's  corpuscle  suspension. 
The  tubes  are  incubated  for  one  hour  and  that  tube 
noted  in  w^hich  the  smallest  amount  of  amboceptor 
(inactivated  rabbit's  serum),  produced  complete 
hemolysis.  This  is  called  the  hemoh^tic  unit  of 
amboceptor. 

The  antigen  is  prepared  by  the  extraction  of 
minced  syphilitic  or  normal  liver,  with  10  volumes 


288  INFECTION     AND     IMMUNITY. 

of  95  per  cent,  alcohol  for  a  week  at  37°  C.  This 
extract  is  filtered  and  evaporated  by  means  of  a 
fan  at  a  temperature  below  40°  C.  The  residue 
is  extracted  with  ether  and  the  ether  evaporated. 
This  residue  is  again  taken  up  in  ether  and  frac- 
tionated twice  with  acetone  to  remove  the  acetone- 
soluble  hemolytic  substances.  The  acetone-insol- 
uble residue  is  evaporated  to  dryness  and  extracted 
with  95  per  cent,  alcohol.  This  solution  is  used 
as  a  stock  antigen  and  suspensions  in  salt  solution 
are  used  as  material  for  tests. 

A  titration  of  antigen  should  then  be  carried 
out  as  follows :  A  serum  from  a  known  case  of 
syphilis  should  be  obtained  and  0.1  c.c.  of  the 
inactivated  serum  added  to  each  of  a  series  of 
tubes.  Another  series  of  controls  is  made  by  the 
use  of  a  like  quantity  of  inactivated  normal  serum. 
To  each  of  the  tubes  of  the  test  series  graded 
varying  amounts  of  antigen  are  added  and  like 
amounts  added  to  the  control  tubes.  Complement 
0.1  c.c.  is  added  to  each  of  all  of  the  tubes  and 
the  set  incubated  one  hour.  At  the  end  of  this 
time,  two  units  of  amboceptor  for  sheep's  cor- 
puscles and  1  c.c.  of  5  per  cent,  suspension  of 
sheep's  corpuscles  are  added  and  the  tubes  incu- 
bated for  another  hour.  The  smallest  amount  of 
antigen  Avhich,  with  the  S3^philitic  serum,  will  bind 
complement,  is  indicated  by  the  tube  containing 
the  lowest  quantity  of  antigen  in  which  hemolysis 
has  not  taken  place.  The  control  tube  containing 
a  like  quantity  of  antigen  but  with  normal  serum 
should  be  completely  hemolyzed. 

Having  now  standardized  both  antigen  and 
hemolytic   amboceptor,  the  test  of  the  serum  in 


TECHNIG  OF  WASSERMANN  REACTION.     289 

question  is  carried  out  as  follows :  0.1  c.c.  of 
inactivated  serum  to  be  tested  is  added  to  0.1  c.c. 
of  complement  and  that  amount  of  antigen  added 
which  was  found  to  be  the  minimum  required  to 
bind  complement  in  the  presence  of  0.1  c.c.  of 
syphilitic  serum.  Control  tubes  are  made  as  fol- 
lows: One  positive  control  is  made  as  the  test 
serum  tube  but  with  a  like  quantity  of  inactivated 
known  syphilitic  serum  in  place  of  the  serum  to  be 
tested.  One  negative  control  is  prepared  with  the 
same  components  as  the  test  serum  tube  except 
that  inactivated  normal  serum  is  used  instead  of 
the  serum  to  be  tested.  Three  control  tubes  are 
made  with  the  test  serum  in  one^  positive  serum  in 
a  second  and  the  normal  serum  in  the  thirds  and 
salt  solution  substituted  for  the  antigen  to  ascer- 
tain whether  or  not  the  serum  alone  causes  com- 
plement deviation.  One  control  tube  is  made  with 
salt  solution  instead  of  serum  to  see  if  antigen 
alone  will  bind  complement.  Another  control  may 
be  made  with  complement,  human  serum  to  be 
tested  and  corpuscles  to  exclude  hemolysins  for 
sheep's  corpuscles  being  present  in  the  human 
serum.  After  incubation  of  the  antigen,  comple- 
ment, serum  mixtures  and  control  tubes  for  one 
hour,  the  hemol3^tic  system,  consisting  of  two 
units  of  hemolytic  amboceptor  and  1  c.c.  of  5  per 
cent,  corpuscle  suspension,  is  added  to  each  tube. 
After  a  second  incubation  of  one  hour  the  tubes 
are  examined  for  hemolysis.  There  should  be  no 
hemolysis  in  the  positive  control  tube.  In  the 
other  control  tubes  complete  hemolysis  should  have 
taken  place.  If  hemolysis  is  present  in  the  tube 
containing  the  test  mixture  the  reaction  is  nega- 


290  INFECTION     AND    IMMUNITY. 

tive,  that  is,  there  is  no  evidence  of  .syphilis.  If 
hemolysis  is  absent  as  in  the  positive  control  tube 
the  reaction  is  characteristic  of  syphilis. 

Various  modifications  of  this  technic  have  been 
used  by  different  experimenters  with  good  results. 
Noguchi,  for  instance,  has  used  human  blood  sus- 
pensions with  their  amboceptor  instead  of  sheep's 
blood,  the  purpose  being  to  avoid  complications 
due  to  hemolysins  for  sheep's  corpuscles  found 
occasionally  in  human  serum.  It  has  been  found 
that  a  larger  number  of  positive  reactions  in 
syphilis  can  be  obtained  by  using  non-heated 
serum  of  the  suspected  patient.  It  is  also  found, 
however,  that  a  larger  number  of  normal  inactive 
serums  react  as  positives;  the  reaction  is  therefore 
not  so  specific  as  when  the  heated  serum  is  used. 
Synthetical  antigens  composed  of  mixtures  of 
lipoid  bodies  of  known  composition,  have  been  used 
with  varying  degrees  of  success. 
Tni«e  of  the  The  Wasscrmaun  reaction  has  proved  to  be  of 
""^^^Reactr^n*  great  value  in  the  diagnosis  of  syphilis.  The  per- 
centage of  positive  reactions  found  in  the  various 
stages  of  syphilis  varies  with  the  technic  of  differ- 
ent observers.  The  following  table  is  made  from 
a  collection  of  percentages  by  Pearce : 

Highest  Lowest 

Stage  of  Disease  per  cent,  per  cent. 

Primary  syphilis 92.8  64.4 

Secondary  syphilis    100  71 

Tertiary  syphilis 100  63 

Early  latent  syphilis 76  51 

Late  latent  syphilis 79  46 

Hereditary  syphilis 100  86 

The  percentage  of  cases  in  which  syphilis  could 
be  excluded  so  far  as  possible  from  history  and 


WAS8ERMANN     REACTION.  291 

negative  clinical  symptoms,  and  which  gave  a 
positive  reaction,  varies  from  0.3  to  3.6  per  cent. 

The  results  in  the  parasyphilitic  diseases  are  as 
follows :  In  tabes,  using  blood  serum,  the  average 
of  positive  reactions  is  62.88  per  cent.;  using 
cerebrospinal  fluid.  56.2  per  cent.  In  general 
paresis,  using  blood  serum,  88.1  per  cent,  of  cases 
are  positive,  with  cerebrospinal  fluid  90  per  cent. 
(Noguchi). 

The  earliest  appearance  of  the  Wassermann  re- 
action is  that  reported  by  Lesser,  eight  days  after 
exposure.  The  reaction  usually  appears  by  the 
end  of  the  fourth  week  after  the  appearance  of  the 
chancre. 

Among  non-S3'philitic  diseases  the  Wassermann 
reaction  has  been  observed  in  trypanosomiasis,  in 
leprosy  with  less  constancy,  in  scarlet  fever  (usu- 
ally weakly  positive  and  transient),  in  frambesia, 
tuberculosis  and  carcinoma.  In  these  non-syph- 
ilitic diseases,  the  ones  giving  the  highest  per 
cent,  positive  reactions  are  those  least  likely  to  be 
confused  with  syphilis.  The  reactions  found  a.t 
times  in  carcinoma  and  tuberculosis  may  be  due 
to  concurrent  syphilis. 

Specific  treatment  has  been  found  by  all  ob- 
servers to  have  a  profound  influence  on  the 
Wassermann  reaction  and  disappearance  of  the 
test  has  been  observed  after  treatment  for  from 
six  months  to  five  3'ears. 

A  positive  reaction  is  therefore  regarded  by 
many  observers  as  an  indication  for  further 
treatment. 


CHAPTEE   XVIII. 


Cytotoxin     or 
Cytolysin. 


•      CYTOTOXINS. 

Following  the  discovery  of  immune  hemolytic 
serums  it  was  a  short  step  to  experiments  which 
Involved  immunization  with  various  other  tissue 
cells,  and  as  a  result  of  such  work  we  are  to-day 
familiar  with  antiserums  for  almost  every  organ 
of  the  body. 

Metclniikoff  gave  the  name  of  cytotoxins  to  those 
serums  which  destroy  cells  other  than  bacteria 
and  erythrocytes;  the  word  cytolysin  is  used  syn- 
onymously. Naturally  a  serum  which  destroys  any 
cell  whatsoever  is  c3'totoxic,  but  according  to  the 
rather  loose  custom  which  prevails,  we  speak  of 
bacterioh^sins,  hemolysins  and  other  cytolysins,  in- 
cluding among  the  latter  serums  which  destroy 
leucocytes,  the  cells  of  the  liver,  kidney  and  other 
organs. 
J  Cytotoxins  are  of  interest,  not  only  because  they 
utility^  of  are  produced  in  accordance  with  the  general 
laws  of  anti-body  formation,  but  they  have,  in  ad- 
dition, a  certain  theoretical  and  perhaps  practical 
importance.  Immediateh''  on  their  discovery  the 
possibility  became  manifest  that  they  might  be 
utilized  in  the  elucidation  of  certain  physiologic 
and  pathologic  problems.  For  example,  by  put- 
ting the  thyroid  out  of  function  through  in- 
jections of  thyrotoxic  serum  it  might  be  pos- 
sible to  confirm,  or  to  prove  incorrect,  cer- 
tain theories  as  to  the  role  of  the  gland  in 
pietabolism.  Or,  by  the  selective  destruction  of  a 
tissue,    facts   concerning   its    regenerative   powers 


Cytotoxins. 


SPECIFICITY     OF     CYTOTOXI^'S.  293 

might  be  learned.  The  use  of  an  antipancreatic 
serum  might  throw  some  light  on  the  nature  of 
diabetes.  Therapeutic  possibilities  also  suggested 
themselves.  One  might  be  able  by  means  of  artifi- 
cial anticytotoxic  serums  to  counteract  cytotoxins 
which  were  being  formed  pathologically  in  the 
body.  Or,  by  injecting  small  amounts  of  a  cyto- 
toxin,  perhaps  one  could  stimulate  to  a  renewed 
production  of  the  homologous  cells ;  small  doses  of 
a  hemolytic  serum  might  be  useful  in  combating 
anemias.  Or  small  amounts  of  leucotoxic  serum 
might  cause  an  increase  in  the  number  of  leuco- 
cytes, and  thereby  an  increased  resistance  to  infec- 
tion. Perhaps  autocytotoxins  are  formed  in  some 
such  manner  as  the  following:  An  extraneous 
toxic  substance  causes  the  destruction  of  a  few 
kidney  cells,  the  constituents  of  the  latter  reach 
the  circulation  and  stimulate  other  organs  to  the 
formation  of  autonephrotoxic  amboceptors,  which 
then  assist  in  the  destruction  of  more  renal  tissue, 
with  the  result  that  a  vicious  cycle  is  set  up. 

In  spite  of  so  many  theoretical  values,  the  study 
of  cytotoxic  serums  has  not  yielded  the  results 
which  were  anticipated,  perhaps  chiefly  because  of 
their  lack  of  specificity  (Pearce  and  others).  Al- 
though the  cells  of  the  different  organs  differ  wide- 
ly in  their  morphology  and  function,  there  are  no 
doubt  certain  chemical  constituents  (receptors) 
which  they  possess  in  common.  Of  this  we  have 
experimental  proof  from  the  fact  that  immuniza- 
tion with  one  tj^e  of  cell  yields  a  serum  which  is 
toxic  for  the  cells  of  various  organs.  It  is  difficult 
or  impossible  to  injure  one  organ  to  the  exclusion 
of  all  others  by  means  of  a  cytotoxin.  One  may 
attempt  to  purify  a  C5i:otoxic  serum  through  ab- 


L,ack    of 
Specificity 


294  INFECTION     AND     IMMUNITY. 

sorption  of  the  adventitious  amboceptors  by  means 
of  the  corresponding  cells.  Inasmuch,  however,  as 
the  result  is  a  decrease  in  the  chief  amboceptors 
as  well  as  of  the  adventitious,  the  desired  object  is 
not  fully  realized.  Theoretically  the  cytotoxic 
treatment  of  malignant  tumors  offers  an  impor- 
tant field  for  research.  But  here,  too,  various  dif- 
ficulties are  involved,  as  lack  of  specificity  of 
serums  and  the  multiplicity  of  cell-types  which 
constitute  different  tumors. 
Determina-       Experiments  with  cj^totoxic  serums  may  be  con- 

*ta"ic**  Action'  ^^^ctcd  in  vitvo  or  in  the  living  animal.  In  either 
case  a  necessary  condition  for  the  recognition  of 
the  cytotoxic  action  is  the  presence  of  some  dis- 
tinctive sign  of  vitality  on  the  part  of  the  cell,  the 
loss  of  which  may  be  taken  as  evidence  of  cell- 
death.  Loss  of  motility  and  of  proliferative  power 
indicate  the  death  of  bacteria,  and  solution  of 
hemoglobin  the  death  of  erythrocytes.  Under  par- 
ticular conditions  loss  of  motility  on  the  part  of 
certain  tissue  cells,  as  spermatozoa,  leucocytes  and 
ciliated  epithelium,  is  an  evidence  of  cell  death  or 
cell  injury.  The  toxic  action  of  serums  on  cells  of 
fixed  form  is  more  difficult  to  determine,  and  for 
evidence  one  must  rely  on  such  points  as  clearing 
of  the  protoplasm  (digestion?),  swelling  of  the 
cell  and  nucleus,  actual  solution  of  the  cytoplasm, 
or  degenerations  of  the  homologous  organs  when 
the  serum  is  injected  into  the  living  animal. 
Technic  of       '^^^  techuic  of  immunization  with  tissue  cells  is 

inimniiization  similar  to  that  of  immunization  with  bacteria.  In 
order  to  obtain  leucocytes  in  abundance,  artificial 
leucocytosis  is  produced  in  the  peritoneal  or  pleural 
cavity   by   the    injection    of   bouillon,    or    l}Tnph 


SPERMOTOXIN.  295 

glands,  spleen  or  bone-marrow  may  be  ground  up 
and  injected. 

Immunization  with  solid  organs,  as  liver,  kidney 
or  testicle,  is  easily  accomplished,  a  necessary  pre- 
liminary for  injection  being  a  thorough  disintegra- 
tion of  the  tissue  by  grinding  with  sterile  sand; 
the  resulting  mass  when  suspended  in  salt  solution 
passes  through  the  injecting  needle  readily. 

Cytotoxins,  like  bacteriolysins  and  hemolysins,  Amijoceptors, 
are  complex  substances,  in  that  they  consist  of  am-  an™^\ttVcvt*o- 
boceptors    and    complements.     The    amboceptors  toxins. 
alone  are  increased  during  immunization,  the  com- 
plement being  a  normal  constituent  of  the  serum 
of  the  animal.     The  phenomena  of  inactivation 
and  reactivation  are  observable  here  as  in  connec- 
tion with  other  cytol3^ic  serums.     Anticytotoxins 
are  readily  produced  by  immunization  with  many 
cytotoxins;  the  antiserum  usually  consists  of  anti- 
complement,  but  in  some  instances  antiambocep- 
tors  have  been  described. 

Simultaneously,  or  nearly  so,  Landsteiner  in  spermot«xin. 
Vienna  and  Metchnikoff  in  Paris  reported  the 
production  of  spermotoxic  serums  by  immuniza- 
tion with  spermatozoa,  the  natural  motility  of 
which  rendered  the  recognition  of  cell  death  easy. 
The  technic  which  Landsteiner  first  employed  was 
that  of  the  Pfeiffer  experiment  in  that  he  immun- 
ized guinea-pigs  with  the  spermatozoa  of  cattle  and 
observed  loss  of  motility  on  the  part  of  the  cells 
when  they  were  injected  into  the  peritoneal  cavity 
of  the  immunized  animals.  Comparable  with 
many  other  cytotoxins,  spermotoxin  kills  the  ho- 
mologous cell  without  causing  its  solution.  The 
loss  of  motility  is  also  observed  in  hanging-drop 
preparations  provided  a  fresh  or  a  complemented 


2i)G  INFECTION     AND     IMMUNITY. 

serum  is  used.  Most  normal  serums  show  a 
greater  or  less  degree  of  toxic  action  for  the  sper- 
matozoa of  other  animals,  and  normal  spermotox- 
ins  like  the  immune  consist  of  amboceptor  and 
complement.  Metchnikoff  claims  to  have  pro- 
duced an  autospermotoxin  by  immunizing  guinea- 
pigs  with  the  spermatozoa  of  other  guinea-pigs. 

AVhen  a  spermotoxic  serum  is  injected  into  the 
living  animal  it  is  thought  that  the  amboceptors 
are  taken  up  by  the  homologous  cells,  and  this 
would  seem  to  affect  the  vitality  of  the  sperma- 
tozoa, inasmuch  as  De  Leslie  rendered  male  mice 
sterile  for  16  to  20  days  by  the  injection  of  the 
serum. 

It  is  of  theoretical  interest  that  castrated  ani- 
mals will  yield  spermotoxin  by  immunization, 
showing  that  the  amboceptors  are  not  of  necessity 
produced  by  the  analogous  ti:ssue  of  the  immun- 
ized animal.  From  the  fact  that  spermotoxic 
serums  are  hemolytic,  it  is  assumed  that  certain 
receptors  are  common  to  erythrocytes  and  sperma- 
tozoa. Hemolytic  serums,  on  the  other  hand,  may 
not  be  spermotoxic.  There  is  nothing  contradic- 
tory in  this  lack  of  reciprocal  action,  for  those  re- 
ceptors which  are  common  to  the  two  cells  may  not 
be  important  for  the  life  of  the  spermatozoon, 
whereas  the  oppo'site  condition  prevails  with  the 
erythrocyte. 

It  is  certainly  of  interest  that  immunization  with 
the  plasma  of  ova  causes  the  formation  of  spermo- 
toxic amboceptors,  a  fact  which  points  to  certain 
common  constituents  of  the  two  cells. 

Antispermotoxin  may  be  produced  by  immuniza- 
tion with  spermotoxic  serum  (anticomplement  or 
anti  amboceptor) . 


LEUC0T0X1N8.  297 

Following  teclmic  similar  to  that  employed  by  cytotoxin 
Landsteiner,  von  Dungern  obtained  a  cytotoxic  E*iJinieiAim'! 
serum  for  ciliated  epithelium  of  the  trachea.  The 
cells  disintegrated  in  the  peritoneal  cavity  of  the 
immunized  animal,  but  not  in  that  of  the  normal 
animal.  This  serum  also  proved  to  be  hemolytic 
in  spite  of  the  fact  that  no  er3^throcytes  were  in- 
cluded in  the  injections.  That  the  receptors  which 
characterize  ciliated  epithelium  are  widely  distrib- 
uted is  shown  by  the  fact  that  immunization  with 
cow^s  milk  causes  the  formation  of  a  cytolytic 
serum  for  the  tracheal  epithelium  of  the  cow. 

Leucotoxic,  lymphotoxic  or  lymphatotoxic 
serums  are  prepared  by  immunization  with  ex- 
udates which  are  rich  in  leucocytes,  or  with  the 
emulsions  of  lymphoid  organs:  lymph  glands, 
spleen,  bone  marrow.  Metchnikoff  prepared  the 
first  serum  of  this  nature  by  the  injection  of  the 
spleen  of  rats  into  guinea-pigs.  Leucotoxic  serums 
are  toxic,  not  only  for  leucocytes,  but  also  for  red 
corpuscles  and  endothelial  cells.  When  injected 
into  the  peritoneal  cavity  the  endothelium  is 
thrown  off,  and  when  given  subcutaneously  the 
capillary  endothelium  is  attacked,  with  the  result 
that  blood  escapes  to  form  a  large  hematoma.  The 
action  of  the  serum  on  leucocytes  may  be  observed 
in  vitro.  The  mononuclear  cell-s  are  often  more 
susceptible  than  the  polymorphonuclears,  although 
this  depends  somewhat  on  the  animals  and  the 
particular  organ  used  for  immunization.  The  cells 
lose  their  motility,  the  cytoplasm  becomes  trans- 
parent, and  swells  to  form  a  large  clear  vesicle, 
which  appears  to  be  surrounded  by  a  sharp,  thin 
membrane.  The  cell  contents  may  be  discharged 
or  entirely  liquefied,  the  nucleus  alone  being  rec- 


298  INFECTION     AND     IMMUNITY. 

ognizable.     Leucocytes    are   agglutinated   by   the 
serum.     A  strong  leucotoxic  serum  may  be  fatal 
to  the  animal  when  injected  into  the  peritoneal 
cavity  or  blood  stream,  the  exact  cause  of  death 
being  obscure. 
Old  Age.       Metchnikoff,  taking  the  view  that  the  phenom- 
ena of  old  age  depend  on  the  destruction  of  vari- 
ous tissue  cells  by  the  mononuclear   leucocytes 
(macrophages),  expressed  the  hope  that  a  lympho- 
toxic  serum  might  be  utilized  to  combat  the  action 
of  these  cells  with  the  result  that  life  would  be 
prolonged.     Whether  or  not  his  view  as  to  the 
cause  of  old  age  is  correct,  his  plan  of  antagonizing 
it  had  to  be  abandoned  because  leucotoxic  serums 
do  not  injure  the  macrophages  to  the  exclusion  of 
other  leucocytes. 
Effect  of       The  injection  of  a  leucotoxic  serum  into  the  per- 
sernm''on**Ri-   itoucal  cavity  of  a  guinea-pig  causes  a  temporary 
%*'*S**"5®  ***  decrease  in  the  number  of  leucocytes,  and  durinor 

Infections.         ,  j         ?  o 

this  period  of  hypoleucocytosis  the  resistance  of  the 
animal  to  peritoneal  infections  with  the  organisms 
of  typhoid  and  cholera  is  lowered.  One  may  refer 
this  effect  to  the  destructive  action  of  the  serum 
on  the  leucocytes,  by  which  phagocytosis  is  pre- 
vented, or,  according  to  Wassermann,  it  may  de- 
pend on  the  action  of  anticomplement  which  the 
leucotoxic  serum  contains.  (Leucocytes  contain 
complement,  hence  immunization  with  leucocytes 
causes  the  formation  of  anticomplement.)  It  is 
probable  that  both  factors  are  of  influence.  In  the 
course  of  from  twenty-four  to  forty-eight  hours 
after  peritoneal  injection  of  the  serum,  the  leuco- 
cytes reaccumulate  to  an  enormous  extent.  Dur- 
ing this  secondary  hyperleucocytosis  resistance  to 
•  peritoneal  cholera  or  typhoid  is  increased.     Some 


NEPHROTOXINS. 


299 


Nephrotoxic 
Serum. 


non-toxic  substances,  as  bouillon,  have  a  similar 
effect,  and  although  the  seconclan^  leucocytosis  is 
never  so  great  as  that  caused  by  the  leucotoxic 
serum,  the  protective  action  is  equally  high.  It 
would  seem  that,  leucocyte  for  leucocyte,  those 
which  accumulate  following  the  injection  of  leuco- 
cytoxic  serum  are  less  efficient  in  antibacterial 
action  than  those  whose  presence  is  caused  by 
nontoxic  substances  (Eicketts).  Hence  there  prob- 
ably is  no  field  for  leucotoxic  serum  as  a  means  of 
temporarily  increasing  resistance  to  bacterial  in- 
fections. 

By  guarded  immunization  Besredka  obtained  an 
antileucotoxic  serum. 

Nephrotoxic  serums  have  been  brought  into 
close  relationship  with  clinical  and  anatomic  prob- 
lems by  a  number  of  investigators.  Some  normal 
serums  are  held  to  be  nephrotoxic  inasmuch  as 
their  injection  is  followed  by  albuminuria  and 
renal  degenerations.  Immune  nephrotoxins  have 
a  similar  but  more  pronounced  effect,  and  Linde- 
man  referred  the  death  of  his  experiment  animals 
to  the  development  of  a  uremic  condition.  Of 
more  than  ordinary  interest  is  the  claim  of  cer- 
tain workers  that  autonephrotoxins  may  be  formed  Antinepiiro- 
in  the  body.  One  (Lindeman)  caused  a  toxic 
nephritis  in  dogs  by  the  injection  of  potassium- 
bichromate.  The  serum  of  this  dog,  although  free 
from  chromic  acid,  was  toxic  for  other  dogs,  pro- 
ducing the  symptoms  which  are  caused  by  an  im- 
mune nephrotoxic  serum.  It  was  supposed  that 
the  chromic  acid  in  the  fir'st  dog  caused  disintegra- 
tion of  renal  cells  and  that  the  constituents  of  the 
latter  were  then  taken  up  by  nephrotoxic  receptors 
which  normally  reside  in  the  organs  of  the  ani- 


toxins. 


300  INFECTION     AND     IMMUNITY. 

mal;  as  a  result  the  receptors  were  overproduced 
and  their  presence  became  manifest  when  the 
serum  was  injected  into  other  dogs.  In  accord- 
ance with  this  view  the  original  toxic  cause  of  a 
degenerative  nephritis  would  be  of  less  conse- 
quence for  the  continuance  of  the  condition  than 
the  formation  of  the  nephrotoxic  amboceptors ;  i.  e., 
the  formation  of  an  autonephrotoxin. 

Somewhat  similar  results  were  obtained  by  oth- 
ers through  ligation  of  the  renal  vein  or  artery  on 
one  side.  Constituents  of  cells  of  the  isolated  kid- 
ney were  supposed  to  be  absorbed,  and  as  a  conse- 
quence nephrotoxic  amboceptors  were  produced  in 
excess  by  organs  of  uncertain  identity.  To  the 
action  of  the  new-formed  bodies  were  attributed 
the  degenerative  changes  which  were  found  in  the 
opposite  kidney,  and  the  nephrotoxic  properties 
which  the  serum  manifeested  when  injected  into  a 
healthy  animal  of  the  same  species. 
Antinepiiro-  Accordiug  to  Ascoli  and  Figari  unilateral  neph- 
*H^'*Vert^ro**iiv*^  rcctomy  so  injures  the  opposite  kidney  (overwork) 
that  the  serum  of  the  animal  becomes  nephrotoxic. 
They  state  also  that  an  animal,  the  serum  of  which 
contains  nephrotoxin,  may  antagonize  the  latter 
by  the  production  of  antinephrotoxin,  and  suggest 
that  spontaneous  recovery  from  nephritis  may  be 
due  to  the  action  of  such  an  antibody.  They  would 
account  for  the  cardiac  h5^pertrophy  of  nephritis 
by  the  action  of  nephrotoxic  serum  in  causing  con- 
traction of  the  peripheral  vessels  with  consequent 
increase  of  blood  pressure;  and  for  the  nervous 
symptoms  on  the  basis  that  the  serum  contains  a 
neurotoxic  constituent. 

We  hardly  dare  consider  such  far-reaching  con- 
clusions as  decisive  until  they  have  been  extensively 


OTHER    CYT0T0XIN8. 


301 


toxins. 


Neurotoxins. 


confirmed.  Yet  whatever  may  be  their  real  value 
they  serve  to  emphasize  the  possibility  that  those 
principles  which  are  so  important  in  relation  to 
im.munity  against  infections  diseases,  may  be 
equally  important  in  relation  to  other  pathologic 
conditions. 

Hepatotoxins  have  been  obtained  by  a  number  Hepato- 
of  workers,  and  the  attempt  has  been  made  to  pro- 
duce autohepatotoxins  by  injecting  liver  tissue  of 
the  guinea-pig  into  animals  of  the  same  species. 
The  success  was  not  unqualified.  Hepatotoxins 
when  injected  are  reported  to  cause  insular  degen- 
erations of  the  liver;  however,  the  lesions  may  be 
caused,  in  part  at  least,  by  capillary  emboli  of  en- 
dothelial cells  or  erythrocytes. 

Neurotoxic  serums  have  been  studied  with  some 
thoroughness.  Whether  one  injects  the  cerebrum, 
cerebellum  or  spinal  cord,  the  resulting  serums 
apparently  are  similar;  either  an  anticerebral  or 
an  anticerebellar  serum  will  cause  degenerations 
of  the  spinal  ganglion  cells.  In  view  of  their 
broad  range  of  action  it  seems  improbable  that 
neurotoxic  serums  will  be  of  service  in  clearing  up 
the  etiology  of  system  degenerations  of  the  nervou's 
tracts.  They  are  usually  hemolytic  and  hemag- 
glutinating  and  may  also  be  endotheliotoxic  and 
leucotoxic.  When  mixed  with  emulsions  of  the 
homologous  brain  tissue  the  neurotoxic  ambocep- 
tors are  bound  by  the  receptors  of  the  nervous  tis- 
sue, and  the  serum  consequently  loses  its  toxicity. 
Antineurotoxic  serums  have  been  described. 

Syncjdiolysin  is  the  name  given  to  a  serum  which 
is  obtained  by  immunization  with  the  placenta. 
Certain  writers  (Yeit  and  Scholten,  Charrin  and 
Delamare)  report  that  the  injection  of  placentar 


Cyncytio- 
toxin   in   Re- 
lation   to 
Eclampsia. 


;^02  INFECTION     AND     IMMUNITY. 

tissue  alone  causes  albuminuria,  a  consideration 
which  led  them  to  assume  that  the  placentar  cells 
contain  a  nephrotoxic  substance.  Inasmuch  as 
placentar  cells  or  their  constituents  may  reach  the 
circulation  during  eclampsia  (Schmorl)  it  was 
not  a  long  step  to  suppose  that  the  nephritis  of 
pregnancy  is  due  to  the  toxic  syncytial  cells  which 
are  absorbed.  The  results  which  Weichardt  re- 
ported gave  some  strength  to  the  view  just  cited. 
By  treating  placentar  tissue  of  rabbits  with  the 
specific  cyncytiolj^sin  the  toxin  supposedly  was  lib- 
erated, and  the  mass  when  injected  into  normal 
rabbits  is  said  to  have  produced  symptoms  of  an 
eclamptic  nature.  On  the  basis  of  these  observa- 
tions the  hope  has  been  expressed  that  an  anti- 
toxin for  eclampsia  might  be  prepared  by  immun- 
ization with  placentar  tissue.  However,  the  con- 
ditions are  by  no  means  simple;  any  value  which 
the  destruction  of  circulating  syncytial  cells  or 
their  toxin  would  afford  might  be  more  than  offset 
by  the  action  of  the  hemotoxin  and  neurotoxin 
which  the  serum  is  said  to  contain.  Whether  or 
not  the  hypothetical  toxin  of  syncytial  cells  may 
be  separated  from  the  other  cell  constituents,  and 
whether  immunization  with  the  toxin  will  yield 
an  antitoxic  serum  are  possibilities  which  remain 
for  further  investigation;  the  results  cited  have 
not  been  obtained  by  all  observers. 

Liepmann  hopes  for  a  serum-diagnosis  of  preg- 
nancy. If,  as  supposed,  the  blood  of  a  pregnant 
woman  contains  syncitial  cells  or  their  products 
of  degeneration,  the  serum  when  mixed  with 
a  specific  syncytiolysin  may  cause  a  precipitate. 
He  claims  to  have  demonstrated  the  presence  of 


NUCLEOPROTEID     IMMUNIZATION.         303 

placentar  constituents  in  the  circulation  by  this 
biologic  method. 

Antithyroid  serum  is  prepared  by  immuniza-  Tiiyrotoxin. 
tion  with  ground-up  thyroid  tissue  or  with  extracts 
of  the  organ.  It  is  hemolytic,  even  though  all  the 
blood  has  been  washed  from  the  tissue  which  was 
injected.  Portis  immunized  with  the  "colloid" 
material  of  the  gland  obtaining  a  hemolytic  thyro- 
toxic serum.  When  injected  into  the  living  animal 
degenerative  changes  are  produced  in  the  thyroid, 
and  some  authors  report  the  tetanic  phenomena 
which  often  follow  surgical  removal  of  the  thyroid. 
In  very  careful  work,  however,  Portis  could  not 
produce  "the  exact  picture  presented  by  thyrodec- 
tomized  animals.'^  Degenerative  changes  were 
found  in  various  organs,  as  liver,  spleen  and  kid- 
neys. 

With  the  idea  of  preparing  an  antigen  which 
would  contain,  so  far  as  possible,  only  substances 
characteristic  of  variety  of  cells  used,  Beebe  has 
made  use  of  nucleuproteids  of  various  organs,  espe- 
cially thyroid  gland,  to  produce  antiserums.  His 
results  would  indicate  that  in  this  way  serums  may 
be  obtained,  which  are  specific  for  different  vari- 
eties of  cells  except  in  high  concentration. 

With  the  use  of  such  a  thyrotoxic  serum  he  has 
reported  good  results  "in  cases  of  hyperthyroidism. 

Pearce  has  failed  to  confirm  these  results  and 
obtains  results,  with  neucleoproteid  as  antigen, 
which  are  similar  to  those  which  he  obtained  with 
simple  extracts. 

Beebe,  however,  criticises  the  technic  of  Pearce 
in  that  Pearce  heated  his  preparation,  thus,  accord- 
ing to  Beebe,  destroying  the  specific  biologic  char- 
acter of  the  extract. 


304 


INFECTION     AND     IMMUNITY, 


Synipatlietic 
Opiitlialinia. 


Pancreotoxiii. 


Otlier 
Cytotoxiiis. 


Toxin     of 
Exlianstioii. 


It  would  appear  that  further  observations  are 
desirable  before  conclusions  can  be  drawn  regard- 
ing the  value  of  nucleoproteid  as  antigen. 

Brown  Pusey  has  made  the  interesting  sugges- 
tion in  regard  to  sympathetic  ophthalmia  that  the 
disease  may  be  due  to  the  formation  of  autocyto- 
toxins  which  are  specific  for  the  cells  of  the  inner 
surface  of  the  ciliary  body  and  iris.  The  disinte- 
gration products  of  the  corresponding  cells  in  the 
eye  which  was  primarily  injured  would  constitute 
the  stimulus  to  the  formation  of  the  specific  anti- 
bodies. The  possibility  is  as  yet  a  problematic 
one. 

The  experimental  study  of  cytotoxic  serums  for 
the  pancreas  has,  up  to  the  present  time,  thrown 
little  light  on  pancreatic  diseases.  It  stated  that 
the  serum  may  cause  transient  glycosuria,  and  it 
is  said  to  have  an  antitryptic  action  in  experiments 
performed  in  the  test-glass. 

The  results  of  different  observers  concerning  the 
action  of  antiserums  for  the  adrenal  gland  are  not 
in  entire  accord.  Although  degenerative  changes 
may  be  caused  in  the  gland  when  the  serum  is  in- 
jected, the  action  is  not  specific;  the  serum  may 
be  highly  hemolytic  (Abbott). 

Ceni  claims  to  have  demonstrated  in  the  circula- 
tion of  epileptics  a  cytotoxin  which  causes  the  ep- 
ileptic attacks,  and  reports  the  production  of  a 
specific  antitoxin. 

Welch ardt  has  published  descriptions  of  a  toxin 
which  is  peculiar  to  states  of  exhaustion,  giving 
an  account  of  the  specific  antitoxin  which  he  pro- 
duced by  immunization. 

Other  cytotoxins  which  have  been  prepared,  as 
those  for  the  pituitary  body,  gastric  mucosa  and 


AUTOCYTOTOXINS. 


305 


cardiac  muscle,  have  at  the  present  time  nothing 
more  than  general  biological  interest. 

It  would  seem  that  no  question  in  relation  to  concerning 
cytotoxic  serums  is  more  important  than  the  pos-  toxins. 
sibility  that  autocytotoxins  may  develop  and  in- 
stitute the  vicious  cycle  which  was  mentioned  ear- 
lier. It  is  true  that  the  results  of  some  investiga- 
tors suggest  the  probability  of  such  a  process,  but 
it  would  be  going  too  far  to  say  that  its  existence 
as  an  important  pathologic  law  has  been  estab- 
lished. On  the  contrary,  the  development  of  auto- 
cytotoxins is  one  of  the  rarest  of  occurrences  in 
experimental  work;  and  Ehrlich  has  spoken  of 
the  inability  of  the  body  to  form  such  antibodies 
as  a  condition  of  'Tiorror  autotoxicus."  The  cells 
of  our  kidneys  and  our  erythrocytes  certainly  do  ^ 
degenerate,  and  it  is  quite  possible  that  the  recep- 
tors which  are  thereby  liberated  actually  reach 
C3^totoxic  amboceptors  which  are  situated  in  other 
organs.  In  the  event  that  the  process  extends  to 
this  point,  Ehrlich  assumes  that  the  amboceptors 
are  of  a  sessile  nature,  that  in  spite  of  the  stimula- 
tion to  which  the  cells  are  subjected  the  "sessile 
amboceptors"  may  not  be  overproduced  and  lib- 
erated as  in  the  case  of  antibodies  for  bacterial 
substances  or  for  the  cells  of  other  species.  In 
accordance  with  this  explanation  we  are  saved 
from  intoxications  of  the  nature  in  question  be- 
cause of  the  sessile  nature  of  the  cytotoxic  ambo- 
ceptors. 


*'Horror 
Antotoxicns." 


CHAPTEK   XIX 


PHAGOCYTOSIS. 

As  one  may  learn  from  the  writings  of  Metchni- 

koff,   phagocytosis,   in   its   broad   sense,   exercises 

three   distinct   functions:    nutritional,    resorptive 

and  protective. 

Phagocytosis       Phaffocytosis,  for  purposes  of  nutrition,  is  most 

for    Purposes        .  .  . 

of  xntrition.  highly  developed  in  unicellular  ameboid  organ- 
isms, but  is  found  also  in  animals  of  considerable 
organic  differentiation.  It  is,  perhaps,  nowhere 
more  striking  than  among  certain  myxomycetes, 
which  are  large,  naked,  multinucleated,  protoplas- 
mic masses  belonging  to  the  plant  kingdom,  and 
which  possess  a  peculiar,  slow,  undulating  motility. 
Ingestion  is  accomplished  through  protoplasmic 
arms  (pseudopodia)  which  are  thrown  out  to  en- 
velop tlie  object.  Minute  plant  and  animal  cells, 
living  or  dead,  are  ingested  in  this  manner  by  the 
myxomycetes,  amebae  and  other  unicellular  organ- 
isms and  are  subsequently  digested  by  means  of 
intracellular  ferments.  The  ferments  which  have 
been  extracted  from  such  cells  are  proteohiic  since 
they  digest  gelatin  and  fibrin,  usually  in  an  acid 
but  sometimes  in  an  alkaline  medium;  that  from 
am.eba?  has  been  called  amibodiastase.  In  the  proc- 
ess of  digestion  a  "vacuole,"  acid  in  reaction  and 
containing  the  ferment,  forms  around  the  in- 
gested particle.  In  certain  phagocytic  unicellular 
organisms  the  protoplasm  shows  a  degree  of  differ- 
entiation, a  mouth  and  an  anus  being  simulated  at 
points  where  the  food  is  most  readily  taken  in  and 
discharged.    Instances  are  cited  in  which  ameboid 


CHEMOTAXIS.  307 

organisms  protect  themselves  against  inimical  cells 
by  ingesting,  killing,  and  finally  discharging  or 
digesting  the  latter. 

The  botanist,  Pfeiffer,  first  described  the  phe-  ciiemotaxis. 
nomena  of  negative  and  positive  chemotaxis  in  re- 
lation to  the  myxomycetes.  Under  certain  condi- 
tions they  either  are  attracted  toward  or  move 
from  moist  places.  That  a  negative  chemotaxis 
may  be  changed  into  a  positive  was  shown  in  rela- 
tion to  salt  solutions.  When  placed  in  the  vicinity 
of  or  in  contact  with  strong^  solutions  the  cell  re- 
cedes,  whereas  if  one  passes  gradually  from  weaker 
to  stronger  solutions  the  latter  eventually  attract 
rather  than  repel  the  cell. 

As  one  sroes  his/her  in  the  animal  scale  intracel-   intestinal 

,     ,  T  «  p  .  .  Phagocytes. 

lular  digestion  for  purposes  of  nutrition  is  con- 
fined to  rather  definite  groups  of  cells.  The  intes- 
tinal epithelium  of  certain  invertebrates  consists 
of  "sessile  pliagocytes,^^  cells  which,  individually 
or  after  fusion  into  plasmodial  masses,  surround 
and  digest  solid  particles  of  food.  It  is  said  that 
in  sponges  the  digestive  tract  is  not  sharply  sepa- 
rated from  the  mesodermal  tissue,  and  the  cells  of 
the  latter  share  with  the  former  the  function  of 
intracellular  digestion. 

In  higher  invertebrates  and  in  all  vertebrates 
the  intestinal  epithelium  ceases  to  be  essentially 
phagocytic,  digestion  being  accomplished  rather  by 
ferments  which  have  been  secreted  by  the  intestinal 
and  related  glandular  epithelium.  Such  animals, 
nevertheless,  possess  an  abundance  of  phagocytic 
cells,  but  they  are  in  the  main  mesoblastic  in  na- 
ture, and  may  have  nothing  more  than  a  remote 
relationship  to  the  nutrition  of  the  organism. 


308  INFECTION     AND     IMMUNITY. 

Macropiiagres  Metchnikoff  divides  the  phagoc3^tic  cells  of  ver- 
piiage*^'  tebrates  into  the  macrophages  and  the  micro- 
phages.  T]ie  macrophages  or  large  phagocytes  in- 
clude the  large  lymphocytes,  endothelial  cells, 
ameboid  connective  tissue  cells  and  others  which 
may  occasionally  take  up  foreign  particles.  Our 
polymorphonuclear  leucoc3^tes  are  the  micro- 
pliages.  In  relation  to  immunity  we  are  concerned 
chiefly  with  the  large  lymphocytes  (macrophages), 
and  the  polymorphonuclear  leucocytes  (micro- 
phages).  Although  such  cells  may  contain  many 
ferments,  Metchnikoff  recognizes  but  one  type  in 
relation  to  their  resorptive,  digestive  and  bacteri- 
cidal activities.  This  he  calls  cytase  and  distin- 
guishes that  of  the  macrophage  as  macrocytase  and 
cytases.  that  of  the  microphage  as  microcytase.  Cytase 
corresponds  to  the  complement  of  Ehrlich.  The 
two  cells  do  not  have  identical  activities,  the  ma- 
crophage being  concerned  specially  in  the  resorp- 
tion of  tissue  cells  and  in  immunity  to  certain 
chronic  diseases,  as  tuberculosis  and  leprosy, 
Avliereas  the  microphage  is  the  cell  which  is  con- 
spicuously antimicrobic  in  relation  to  acute  infec- 
tions. 

According  to  Metchnikoff,  the  leucocytes  are 
very  active  in  the  resorption  of  useless  or  foreign 
cells.  During  the  metamorphosis  of  certain  in- 
vertebrates it  is  said  that  the  larval  tissues  are 
englobed  and  digested  by  wandering  pha- 
gocytic cells.  In  involution  of  the  uterus 
the  muscular  tissue  is  invaded  by  leuco- 
cytes which  take  up  and  digest  or  carry  away  tht 
'Retrogressive  elements."  Metchnikoff's  concep- 
tion   of   certain    atropliic    processes,    particularly 


Resorption   of 
Xative   Cells. 


PHAGOCYTES     AND     RESORPTION.  309 

those  which  are  grouped  among  the  senile  atro- 
phies, is  of  interest  to  pathologists.  In  sclerotic 
atrophy  of  the  ovaries  the  large  lymphocytes  in- 
vade the  tissue,  surround  and  destroy  the  ova  and 
follicular  epithelium  and  eventually,  as  fibroblasts, 
participate  in  the  formation  of  fibrous  tissue  which 
to  a  degree  is  substituted  for  the  original  struc- 
ture. In  old  individuals  or  in  those  of  failing  . 
mentality  it  is  said  that  ganglionic  cells  are  found 
in  a  greater  or  less  degree  of  atrophy  because  of 
the  action  of  certain  mononuclear  phagocytes 
(neuronophages)  which  are  contiguous  to  or  form 
a  zone  around  the  cell.  The  neuronophages  may 
represent  mononuclear  cells  from  the  blood  or 
those  of  proliferated  neurogiiar  tissue.  The  best  Tiie  whiten- 
examples  of  this  condition  were  found  in  very  old 
dogs.  The  chromophores  of  the  skin,  according  to 
Metchnikoff,  may  be  considered  as  chromophages. 
Whether  or  not  they  are  of  epithelial  origin,  as  he 
claims,  they  are  said  to  exist  normally  in  the  hairs 
in  a  latent  or  inactive  condition.  As  old  age  comes 
on,  or  as  a  result  of  other  obscure  causes,  their 
attitude  becomes  an  active  one,  and  they  proceed 
to  take  up  and  digest  the  normal  pigments  of  the 
hairs.  Hence,  white  hairs  are  the  result  of  an 
autoparasitism  by  certain  mononuclear  phago- 
cytes. In  muscular  atrophy  it  is  held  that  the 
sarcoplasm  takes  up  the  striated  tissue  after  the 
manner  of  phagocytes. 

We  come  into  closer  touch  with  our  general  sub-  Resorption 
ject  of  immunity  when  we  consider  the  resorptive  ceiis. 
function  of  the  phagocytes  for  cells  which  are  for- 
eign to  the  host,  for  example,  toward  erythrocytes 
which  are  injected  for  the  purpose  of  producing  a 


310  INFECTION     AND     IMMUNITY. 

hemolytic  serum.  Following  such  an  injection  into 
the  peritoneal  cavity  there  occurs  a  great  accession 
of  macrophages  which  ingest  the  er3^throcytes,  dis- 
solve the  hemoglobin  and  eventually  digest  the 
stroma.  The  same  phagocytes  are  involved  in  the 
resorption  of  any  other  foreign  cells  of  animal  ori- 
gin which  may  be  injected.  In  view  of  the  intracel- 
lular hemolysis  by  the  leucocytes,  one  may  suspect 
that  the  latter  contain  a  hemolytic  ferment;  one 
which,  perhaps,  is  analogous  to  the  hemolysin 
(hemolj^tic  amboceptors  and  complement)  of 
Formation   scrums.     On  this  point  there  has  been  sharp  dis- 

of  cytotoxins.  (,^ggJQj^_  Mctchnikoff  cites  observations  to  show 
that  a  ferment  of  this  nature  may  be  extracted 
from  the  lymphoid  organs,  that  it  contains  a  heat- 
susceptible  constituent,  and  that  when  fresh  it 
may  be  used  to  reactivate  a  heated  hemol3i;ic 
serum.  This  would  indicate  that  the  leucocytes 
contain  cytase  (complement),  but  it  is  not  clear 
that  they  would  also  contain  the  fixators  (ambo- 
ceptors). Nevertheless,  the  demonstration  of  an 
intraleucocytic  hemolysin  and  a  knowledge  of  the 
phagocytic  power  of  the  leucocytes  for  erythro- 
cytes form  the  basis  for  Metchnikoff's  belief  that 
serum-hemolysin  is  nothing  more  than  intraleuco- 
cytic hemolysin,  which  under  proper  conditions 
may  reach  the  serum  or  plasma.  By  an  extension 
of  this  conception  it  is  held  that  all  cytolysins  are 
produced  by  the  macrophages. 
Thermosta-       Korschuu  and  Morgenroth,  on  the  other  hand, 

fIin*f^^*orI  obtained  from  lymphoid  and  various  other  organs, 
not  a  thermolabile  hemolysin,  but  one  which  with- 
stands prolonged  boiling — a  coctostabile  hemolysin 
which  is  soluble  in  alcohol,  shows  no  amboceptor- 


sraii     Extracts. 


CYTA8E.  311 

complement  composition,  and  is  incapable  of  yield- 
ing antihemolysin  by  immunization.  These  re- 
sults, Metchnikoff  holds,  are  only  in  apparent  dis- 
cord with  those  obtained  by  himself  and  his  pu- 
pils, and  depend  on  the  raethods  of  extraction 
which  were  employed.  In  order  to  obtain  the  ther- 
molabile  hemol3^sin  uncontaminated  with  the  ther- 
mostabile,  the  extraction  must  be  a  rapid  one.  If, 
on  the  other  hand,  it  is  prolonged,  as  Metchnikoff 
assumes  that  of  Korschun  and  Morgenroth  to  have 
been,  the  intracellular  ferments  digest  the  remain- 
ing cell  constituents,  including  tlie  thermolabile 
hemolysin,  and  the  thermostabile  hemolysin  is  lib- 
erated or  formed  in  the  process. 

Believing  that  cytase,  under  normal  conditions, 
exists  only  within  the  leucocytes,  and  that  its  pres- 
ence outside  these  cells  is  artificial,  Metchnikoff 
cites  experiments  similar  to  the  following  in  sup- 
port of  his  views : 

Given  a  guinea-pig  which  has  been  immunized  cytase  an 

.  ,T     ,1       1  1        T       «  •  r>   r?        1  1         IntracellTilar 

With  the  blood  oi  a  goose :  ii  iresh  goose  corpuscles  substance. 
are  injected  into  the  peritoneal  cavity,  the  cells  are 
hemolyzed  in  the  fluid  without  the  occurrence  of 
phagocytosis.  Two  explanations  of  the  extraleu- 
cocytic  presence  of  cytase  and  fijxators,  which  is  in- 
dicated by  this  result,  are  possible :  first,  that  they 
are  present  normally  and  continuously  in  the  plas- 
ma of  the  immunized  animal,  or,  second,  that  thfey 
become  liberated  at  the  time  the  corpuscles  are  in- 
jected. According  to  Metchnikoff,  the  latter  conten- 
tion prevails  rather  than  the  former.  He  recognizes 
a  phenomenon  which  bears  the  name  of  phagolysis,  piiasroiysis. 
i.  e.,  solution,  partial  or  complete,  of  phagocytes. 
Almost  any  foreign  substance  or  fluid  which  one 


312  INFECTION     AND     IMMUNITY. 

ma}'  choose  to  put  in  contact  with  leucoc3'tes  so 
stimulates  or  injures  them  that  they  discharge  cer- 
tain of  their  constituents.  If  the  fixators  and 
Liberation  cvtasc  are  among  the  constituents  which  are  dis- 
piiagoiysis.  choTgcd  at  the  time* the  injection  is  made,  the 
extracellular  hemolysis  encountered  in  the  experi- 
ment described  above  might  depend  on  the  libera- 
tion of  these  substances  rather  than  on  their  nat- 
ural occurrence  in  the  plasm.a.  If  this  be  true, 
and  if  one  could  in  some  way  fortify  the  leucocytes 
against  phagolysis,  the  plasma  would  remain  free 
from  hemolytic  power.  Metchnikoff  accomplishes 
such  fortification,  i.  e.,  prevents  phagolysis,  by  a 
simple  procedure,  which  demands  nothing  more 
than  the  peritoneal  injection  of  a  small  quantity 
of  bouillon  or  salt  solution  twenty-four  hours  in 
advance  of  the  experiment.  Possibly  by  this 
means  the  leucocytes  have  been  habituated  to  the 
presence  of  a  foreign  fluid,  or  the  new  leucocytes 
which  accumulate  possess  greater  resistance.  What- 
ever the  explanation,  the  erythrocytes  which  are 
injected  at  this  critical  time  are  said  not  to  un- 
dergo extracellular  hemolysis,  but  instead  are  en- 
globed  and  dissolved  by  the  macrophages.  These 
results  and  others  of  a  similar  nature  are  the  basis 
for  the  belief  that  cytase  normally  is  intracellular, 
and  that  it  becomes  extracellular  only  when  the 
leucocytes  are  subjected  to  injurious  influences. 
The  fact  that  the  serum  of  defibrinated  or  coagu- 
lated blood  contains  cytase  is  not  in  discord  with 
such  an  opinion,  for  in  this  instance  also  the  leu- 
cocytes may  be  injured  to  such  a  degree  that  cer- 
tain of  their  constituents  are  discharged.    We  are 


PHAGOCYTOSIS    IN    IMMUNITY.  313 

well  aware  that  fibrin  ferment  is  liberated  under 
these  circumstances. 

It  was  equally  desirable,  if  possible,  to  determine  Fixators 
the  relation  of  fixators  to  the  leucocytes.  The  sit-  JleScocytes!'^ 
nation  is,  however,  very  complex,  and,  although 
Metchnikoff  regards  the  fixators  as  secretion  or  ex- 
cretion products  of  phagocytic  cells,  the  question 
is,  perhaps,  not  definitely  settled.  When  phagoly- 
sis  is  prevented  in  the  manner  described,  the  in- 
jected erythrocytes  may  well  absorb  fixators  from 
the  plasma  and  still  undergo  no  hemolysis  until  en- 
globed  by  the  phagocytes.  It  is  considered  that 
fixators  in  contrast  to  cytase  may  exist  in  the  cir- 
culating plasma. 

Phagocytosis  as  a  feature  of  local  resistance  puasocytosis 
against  microbic  invasion  was  considered  in  rela-  ***  immunity. 
tion  to  inflammation.  We  come  now  to  speak  of 
the  relationship  of  the  leucocytes  to  general 
states  of  immunity,  having  reference  to  the  condi- 
tions which  have  been  designated  as  natural  and 
acquired  antibacterial  immunity,  and  natural  and 
acquired  antitoxic  immunity. 

The  first  expressions  of  Metchnikoff  concerning 
the  antimicrobic  activity  of  phagocytes,  the  power 
of  freeing  the  organism  from  "invaders  of  every 
sort,"  were  made  altogether  from  an  a  priori  stand- 
point in  an  address  delivered  in  1883,  "Ueber  die 
Heilkrafte  des  Organismus."  He  justified  his  po- 
sition on  general  grounds,  having  in  mind  the 
"more  general  phenomena  of  phagocytosis  and  the 
resorption  of  corpuscular  elements,"  as  he  had 
observed  them  in  various  zoological  studies. 

Shortly  there  came  to  him  the  opportunity  of  Natural  im- 
studying  an  infectious  disease  among  the  Daphnia  Bacteria. 


314  INFECTION     AND     IMMUNITY. 

(water-flea),  a  small  transparent  crustacean.  The 
disease  was  caused  by  a  blastomyces  which  forms 
a  long  needle-shaped  spore.  After  being  swal- 
lowed by  the  animal  the  spores  penetrate  the  in- 
testinal wall  into  the  body  cavity  where  they  are 
surrounded,  englobed  and  digested  by  the  white 
blood  corpuscles.  If  this  occurred  Avith  sufficient 
vigor  all  the  spores  were  disposed  of  and  the  ani- 
mal recovered.  Sometimes,  however,  the  spores 
germinated  even  after  they  had  become  intracellu- 
lar, and  when  the  parasitic  cells  reached  maturity 
they  apparently  had  the  power  of  killing  the  leu- 
cocytes through  the  agency  of  a  secretion  peculiar 
to  themselves.  In  the  event  that  the  latter  proc- 
ess was  sufficiently  extensive  the  tissues  were  soon 
overrun  with  parasites  and  death  resulted  from  a 
septicemic  condition.  The  observations  were  made 
in  the  living  transparent  animal. 
Natural  Although  the  example  cited  seemed  convincing, 
it  was,  01  course,  necessary  that  observations 
should  extend  over  many  infectious  processes  be- 
fore phagocytosis  as  the  cause  of  natural  immunity 
could  be  accepted  as  a  general  fact.  This  has  been 
done  on  rather  broad  lines  by  Metchnikoff  and  his 
pupils,  and  the  results  have  served  to  convince 
them  that  the  phagocytes  are  responsible  for  nat- 
ural immunity  in  all  instances,  and  that  the  de- 
gree of  natural  immunity  in  a  given  case  depends 
on  the  degree  of  phagocytosis  which  is  manifested 
against  the  organism.  As  stated  previously,  the 
microphage,  with  its  microcytase,  is  held  responsi- 
ble for  antibacterial  immunity  in  most  instances, 
although  the  macrophage  is  concerned  in  certain 
chronic  infections. 


PHAGOCYTOSIS  AND    VIRULENCE. 


315 


If  an  animal  is  susceptible  to  a  virulent  culture 
of  anthrax,  but  resistant  to  a  weak  culture,  the 
phagocytic  power  is  found  to  be  greater  for  the 
weaker  organism.  The  highly  virulent  culture 
creates  a  condition  of  negative  chemotaxis,  with 
the  consequence  that  leucocytes  are  not  attracted 
and  microbic  proliferation  proceeds  rapidly. 
Without  going  into  details,  studies  of  the  follow- 
ing and  perhaps  other  micro-organisms  have 
strengthened  Metclmikoff  in  his  views :  staphylo- 
cocci, streptococcus,  pneumococcus,  gonococcus, 
vibrio  of  cholera  in  infections  of  the  guinea-pig, 
the  vibrio  of  goose  septicemia  in  relation  to  the 
guinea-pig,  which  is  naturally  immune,  the  spi- 
rillum of  relapsing  fever,  tubercle  bacillus,  yeast 
cells  and  other  fungi,  and  certain  animal  para- 
sites {Trypanosoma  lewisii). 

Most  important  are  certain  conditions  which 
create  a  condition  of  negative  chemotaxis,  or  other- 
wise engage  the  phagocytes  so  that  they  refuse  to 
take  up  the  essential  organism.  Yaillard  says 
that  all  animals  are  immune  to  pure  cultures  of 
the  tetanus  bacillus  or  its  spores,  provided  the  lat- 
ter have  been  washed  entirely  free  of  toxin.  The 
absence  of  toxin  permits  of  positive  chemotaxis 
and  phagocytosis,  whereas  toxin  when  present 
causes  negative  chemotaxis^  and  the  bacilli  pro- 
ceed to  further  toxin  formation.  The  same  is  held 
to  be  true  in  infections  by  some  other  organisms. 

It  seems  to  be  definitely  established  that  con- 
taminating organisms  (pyogenic  cocci.  Bacillus 
prodigiosus)  may  greatly  increase  the  virulence  of 
the  bacillus  of  symptomatic  anthrax.  Bacillus 
Welcliii,  and  the  tetanus  bacillus — anaerobic  or- 


Relatioii    of 
Phaerocytosis 
to   Virulence 
of  Bacteria. 


Toxins   a!ii 
Cause    of 
Xegrative 
Cheniosis. 


Accidental 
Eng'ag'enient 
of    Plias'O- 
cytes. 


316  INFECTION     AND     IMMUNITY. 

ganisms.  On  the  one  hand,  the  secondary  bac- 
teria may  produce  more  favorable  conditions  for 
the  growth  of  the  anaerobes  by  consuming  local 
oxygen,  or,  as  Metchnikofl*  believes,  they  may  so 
engage  the  phagocytes  that  the  latter  have  no  dis- 
position to  take  up  the  essential  organism.  This 
condition  may  be  an  important  one  in  other  mixed 
infections,  as  when  the  streptococcus  complicates 
diphtheria  and  scarlet  fever. 
Acquired  im-  If  tlic  pliagocytic  powcr  is  au  index  of  the  de- 
"^Bacteria!  gr^G  of  natural  antibacterial  immunity,  is  the  same 
correspondence  to  be  recognized  when  the  immun- 
ity is  acquired?  To  answer  this  question  satisfac- 
torily it  is  necessary  to  bring  phagocytosis  in  rela- 
tion to  two  different  types  of  antibacterial  immun- 
ity which  it  is  possible  to  recognize.  Cholera  is  an 
example  of  that  type  of  antibacterial  immunity  in 
which  the  bactericidal  power  of  the  serum  under- 
goes a  great  increase.  It  is  stated  that  anthrax 
represents  another  type  in  which  the  immunity  is 
not  dependent  on  the  bactericidal  power  of  the 
serum.  Probably  the  same  may  be  said  of  acquired 
immunity  to  the  streptococcus,  staphylococcus  and 
the  pneumococcus,  yet  it  is  perhaps  not  definitely 
established  that  the  immunity  in  these  instances 
is  antibacterial  rather  than  antitoxic.  For  the 
present  we  may,  however,  with  Metchnikoff,  con- 
sider that  the  immunity  is  antibacterial  and  that 
it  is  a  cellular  or  phagocytic  immunity. 
Anthrax.  Eabbits  whicli  have  been  immunized  against 
anthrax  respond  to  subcutaneous  or  intraperitoneal 
injection  of  a  virulent  culture  by  concentrating  so 
vast  a  number  of  microphages  at  the  site  of  inocu- 
lation that  the  fluid  becomes  purulent  in  appear- 


RELATION  OF  SERUM  TO  PHAGOCYTOSIS.  317 

ance.  Examination  shows  an  enormous  degree  of 
phagoc3^tosis.  When,  on  the  other  hand,  non-im- 
mune rabbits  are  submitted  to  similar  inocula- 
tions, the  fluid  which  accumulates  locally  is  of  a 
clear  serous  character,  contains  few  leucocytes,  and 
no  phagocytosis  is  observable;  the  animals  die  of  a 
rapidly  developing  septicemia.  From  the  results 
one  may  well  suspect  that  the  immunity  is  related 
to  and  perhaps  coextensive  with  the  acquired  pha- 
gocytic power. 

But  is  the  serum  of  no  influence?    It  has  often   Piiagocytes 

Take    Lp 

been  held  that  phaa^ocytes  take  up  bacteria  only   vimient 

^       °      "^  ^  "^      Bacteria. 

after  the  latter  have  been  injured  or  killed  by  the 
serum  or  plasma.  Metchnikoff  answers  this  objec- 
tion experimentally  by  inoculating  an  immune  rab- 
bit with  anthrax,  withdrawing  some  of  the  exu- 
date at  a  time  when  phagocytosis  is  complete,  and 
injecting  it  into  a  non-immune  rabbit.  The  sec- 
ond animal  dies.  Since  none  but  phagocytized 
bacilli  were  injected  into  the  non-immune  rabbit 
( !),  and  since  the  latter  succumbs  to  anthrax,  it 
seems  not  only  unnecessary,  but  unjustifiable,  to 
assume  that  the  bacteria  must  be  attenuated  by 
the  serum  before  they  can  be  taken  up  by  the  leu- 
cocytes. May  the  serum,  nevertheless,  have  some  Tiie  infinence 
obscure  action  which  may  not  be  included  under 
such  terms  as  bactericidal  and  attenuating?  It 
seems  fairly  well  established  that  anti-anthrax 
serum,  at  least  from  certain  animals,  may  exert  a 
protective  influence  when  injected  into  other  ani- 
mals in  conjunction  with  or  in  advance  of  the  cul- 
ture; 5^et  Metchnikoff  discredits  the  importance  of 
such  protection  and  says  that  "those  properties  of 
the  body  fluids,  as  the  bactericidal,  preventive  and 


318  INFECTION     AND     IMMUNITY. 

agglutinating,  fall  away  into  the  background  in 
such  examples  of  immunit}^"  It  is  the  tendency 
of  the  school  of  Metchnikoff  to  refer  the  protective 
power  of  a  serum  to  its  faculty  of  stimulating  the 
phagocytes  rather  than  to  its  effect  on  the  micro- 
organisms. We  shall  see,  however,  in  speaking  of 
opsonins  (p.  324)  that  even  in  relation  to  anthrax 
the  serum  may  possess  a  distinct  property  which 
facilitates  phagocytosis,  not  by  stimulating  the 
phagocytes  but  by  some  action  on  the  bacteria. 
Cholera  an«i  Concerning  those  diseases  in  which  immunity 
infecrioiTs.  is  characterized  by  a  great  increase  of  the  bac- 
tericidal amboceptors  or  fixators,  Metchnikoff  does 
not  disregard  the  existence  or  importance  of  the 
immune  bodies,  but  rather  seeks  to  show  that  they 
are  a  product  of  phagocytic  activity.  The  con- 
ditions are  held  to  be  similar  to  those  already 
mentioned  in  connection  with  intra  vitam  hemoly- 
sis. That  is  to  say,  microcytase  exists  only  in  the 
leucocytes  of  the  immune  animal  under  normal 
conditions;  it  escapes  into  the  plasma,  or  into  the 
serum  during  coagulation,  only  as  a  consequence 
of  the  phagolysis  already  mentioned.  The  phe- 
nomenon of  Pfeift'er  occurs  only  because  the  in- 
jected culture  injures  the  leucocytes,  resulting  in 
the  liberation  of  microcytase,  which  in  conjunction 
with  the  fixators  causes  the  solution  of  the  vibrio. 
When  phagolysis  is  prevented  by  a  preceding  in- 
jection of  bouillon,  phagocytosis  and  intracellular 
solution  of  the  organisms  entirely  supplant  extra- 
cellular solution. 
intrnvnHeninr  ^^  2,n  immuuc  animal  receives  an  intravascular 
Phagocj-toNis  injection  of  the  vibrio  of  cholera  and  is  sacrificed 
pimgroiy»i«.  shortly,  the  relation  of  the  organisms  to  the  leu- 


ORIGIN  OF  GYTASE.  319 

oocytes  may  be  studied  in  stained  microscopic  sec- 
tions of  the  organs    (lungs).     Leucocytes  which 
have  undergone  phagolysis  are  seen  to  be  clumped 
in  the  pulmonary  vessels  and  in  their  immediate 
vicinity  one   finds  many   micro-organisms   which 
have  been  changed  into  the  characteristic  granules 
by  the  action  of  the  cytase  which  has  escaped  from 
adjacent    leucocytes.     Coincident    with    the    phe- 
nomenon of  phagolysis,  the  leucocytes  lose  their 
phagocytic  power;  hence,  no  bacteria  are  found 
within  the  leucocytes.     On  the   other  hand,   all 
those  vibrios  which  are  remote  from  the  leuco- 
cytes have  a  perfectly  normal  appearance.    Phago- 
lysis in  the  blood  stream  may  be  prevented,  just  as 
in  the  peritoneal  cavity,  by  a  preceding  injection 
of  bouillon  into  the  vessels.    In  this  instance  when 
the  culture  is  injected  no  extracellular  solution  or 
transformation    of    the    organisms    into    granules 
takes  place,  but  as  in  the  peritoneal  cavity,  fheir 
destruction    is    accomplished    entirely    within    the 
microphages.     Metchnikoff  holds  to   the  correct- 
ness of  these  observations  and  interpretations,  al- 
though   contradictory    results    were   obtained    by 
Pfeiffer  and  his  pupils.    As  further  evidence  that 
cytase  does  not  exist  normal^  in  the  plasma  Metch-  Microcytase 
nikoff  cites  the  condition  which  is  found  in  the  ieiiuiar." 
anterior  chamber  of  the  eye  in  immune  animals. 
The  vibrios  continue   unaffected   in  the   aqueous 
humor  until  such  a  time  as  leucocytes  wander  in, 
when  they  are  destroyed  by  phagocytosis.     Hence, 
cytase  does  not  exist  in  the  aqueous  humor,  and 
if  not  in  the  aqueous  humor  it  is  surely  absent 
from  the  plasma;  for  if  present  in  the  plasma  it 
would  reach  the  anterior  chamber  by  a  process  of 


Increase  of 
Fixators  and 


320  IXFECTION     AND     IMMUNITY. 

diffusion.  Similar  conditions  prevail  in  edematous 
fluids.  In  another  instance  a  portion  of  a  vein, 
filled  with  blood,  was  resected  and  centrifugated 
without  the  formation  of  a  clot  (absence  of  pha- 
golysis)  ;  the  plasma  contained  no  cytase.  Also 
Gengou  collected  and  centrifugated  blood  in  tubes 
which  were  coated  with  paraffin,  and  thus  avoided 
clotting;  here  also  cytase  was  absent  from  the 
plasma. 

It  would  seem,  then,  that  two  important  anti- 
of  *p?ia*y"ocytic  bacterial  factors  characterize  immunity  to  cholera 
Power,  ^j^^  similar  infections :  the  development  of  specific 
fixators,  and  a  greatly  increased  phagocytic  power 
on  the  part  of  the  leucocytes.  Metchnikoff  leans 
to  the  view  that  bacteria,  having  absorbed  fixators, 
are  more  readily  phagocytized,  but  no  clear  idea  is 
given  as  to  the  change  which  the  fixators  produce. 
However,  he  would  not  refer  the  increased  phago- 
C3^tic  power  entirely  to  the  influence  of  the  fixa- 
tors. He  believes  that  the  leucocytes  of  the  im- 
mune animal  have  per  se  a  higher  phagoc3'tic 
power  than  that  of  the  normal  animal.  In  anthrax, 
for  example,  the  phagocytic  power  is  height- 
ened in  spite  of  the  fact  that  there  is  no  increase 
in  specific  fixators.  This  view,  however,  is  op- 
posed by  Denys  and  Leclef,  who  found  that  tlie 
leucocytes  of  the  immune  animal,  when  trans- 
ferred to  normal  serum,  had  no  greater  phago- 
cytic power  than  normal  leucocytes. 
Fixatorn  Mctchnikoft'  bclicves  that  fixators,  like  cytase, 
]»nc?oiVimKe!  ^^^  produccd  by  the  microphage.  Tliat  the  lymph- 
oid organs  may  form  certain  fixators  seems  prob- 
able from  the  observations  of  Pfeilfer  and  Marx 
in  regard  to  cholera  and  Wassermann  and  Takaki 


LEUCOCYTIC  PRODUCTION  OF  ANTITOXIN.  321 

in  typhoid.  During  the  process  of  immunization 
and  at  a  time  when  amboceptors  Avere  absent  from 
the  serum  they  couhl  be  demonstrated  in  the  blood- 
forming  organs  (spleen,  lymph  glands,  bone-mar- 
row). Metchnikoff  suggests  that  tliey  may  be  pro- 
duced in  these  organs  by  the  microphages  wliich 
have  wandered  in  after  having  englobed  the  micro- 
organisms. In  contrast  to  cytase  tlie  fixators  read- 
ily abandon  the  leucocytes  which  produced  them 
and  become  a  constituent  of  the  plasma. 

The  leucocytes  have  also  been  brouG^ht  in  rela-  ivatumi 

.  ,  „  .  Iiiimniiity    to 

tionship  to  antitoxic  immunity  and  the  formation  Toxins. 
of  antitoxins.  In  experimental  tetanus  exudates 
which  are  rich  in  leucocytes  contain  more  toxin 
than  does  a  similar  quantity  of  blood.  That  is  to 
say,  the  leucocytes  have  the  power  of  absorbing 
toxins,  and  it  is  held  that  the  natural  immunity 
of  the  animal  depends  on  the  degree  to  which  this 
power  is  present.  The  immunity  of  the  chicken 
to  tetanus  depends  not  on  non-susceptible  nerve 
cells  nor  on  the  presence  of  natural  antitoxin,  but 
on  the  absorbing  power  of  tlie  leucocytes  for  the 
toxin.  Not  only  do  leucocytes  absorb  toxins,  but 
it  is  held  that  they  also  are  the  producers  of  anti- 
toxins. As  compared  with  the  side-chain  tlieory, 
it  is  a  peculiarity  of  the  view  of  Metchnikoff  that 
antitoxin  does  not  represent  a  constituent  of  the 
tissue  cells,  but  rather  the  toxin  itself,  which  has 
been  altered  by  leucocytic  activity  in  a  manner  as 
yet  obscure. 

In   passive   antitoxic   immunity   the  idea   of   a   pasMive  Anti- 
chemical  union  between  toxin  and  antitoxin  does  „*ijyf 
not  meet  with  general  acceptance  among  the  up- 
holders of  the  phagocytic  theory.    It  is  sometimes 


322  INFECTION     AND     IMMUNITY. 

said  that  antitoxins  are  efficacious  from  the  fact 
that  they  stimulate  phagocytosis  (absorption)  of 
the  toxin,  the  latter  then  suffering  disintegration 
in  the  leucocytes. 
snmmary.  The  followiug  statements  summarize  the  phago- 
cytic theory  of  immunity  as  conceived  by  Metdi- 
nikoff : 

1.  Natural  immunity  to  bacteria  depends  on 
and  is  coextensive  with  phagocytosis  and  subse- 
quent digestion  of  the  microbes.  Intraleucocytic 
destruction  of  the  micro-organisms  is  accomplished 
by  the  C3^tase,  possibly  aided  by  intraleucocytic  fix- 
ators. Normal  serum  is  devoid  of  both  fixators 
and  cytase. 

2.  Acquired  immunity  to  bacteria  depends  on 
the  establishment  of  a  heightened  phagocytic  power 
as  the  result  of  immunization  or  infection.  In 
diseases  like  anthrax,  in  which  fixators  are  not  in- 
creased, this  new  power  is  an  acquired  property 
of  the  leucocytes  and  is  independent  of  any  in- 
fluence on  the  part  of  the  serum.  In  diseases  like 
cholera,  the  new  fixators  which  are  formed  may 
render  the  micro-organisms  more  susceptible  to 
phagocytosis,  but  this  is  probably  secondary  to 
increased  function  on  the  part  of  the  phagocytes. 
Both  cytase  and  fixator  are  produced  by  the  pha- 
gocytic cells.  In  acquired  active  immunity  to 
bacteria  the  fixators  may  be  free  in  the  serum 
and  plasma,  but  the  cytase  is  intracellular.  In  all 
cases  cytase  becomes  extracellular  only  as  the  re- 
sult of  phagolysis. 

3.  In  passive  immunity  to  bacteria,  as  when  an 
antibacterial  serum  is  injected  for  the  sake  of 
prophylaxis  or  cure,  the  serum  is  efficacious  chiefly 


SUMMARY.  323 

because  it  stimulates  the  leucocj^tes  to  increased 
phagocytosis. 

4.  Natural  immunity  to  toxins  depends  on  the 
power  of  the  leucocytes,  and  perhaps  the  genera- 
tive organs,  to  absorb  the  toxin. 

5.  Active  immunity  to  toxins  is  established 
through  the  activity  of  the  leucocytes,  by  which 
the  toxin  is  probably  so  changed  as  to  constitute 
antitoxin. 

6.  In  passive  antitoxic  immunity  the  antitoxin 
presumably  acts  by  stimulating  the  phagocytes  to 
an  increased  absorption  of  the  toxin. 


CHAPTER   XX 


OPSONINS. 


Although  the  importance  of  the  influence  of 
the  serum  in  phagocytic  processes  was  recognized 
by  Denys  and  Leclef,  it  remained  for  Wright  and 
Douglas  to  demonstrate  that  substances  exist  in 
the  serum  which  are  capable  of  rendering  bacteria 
susceptible  to  phagocytosis.  The  name  opsonin 
which  they  applied  to  this  substance  has  come 
into  general  use. 

The  proof  of  the  action  of  opsonin  on  bacteria 
was  based  on  the  following  facts:  1.  When  the 
fresh  defibrinated  blood  of  some  animal  is  mixed 
with  the  culture  of  a  suitable  micro-oro-anism 
(staphylococcus,  streptococcus,  anthrax  bacillus, 
etc.)  and  placed  in  the  thermostat  for  20  or  30 
minutes,  stained  preparations  of  the  mixture  show 
that  the  polymorphonuclear  leucocytes  contain  a 
large  number  of  the  microbes.  2.  If,  however,  all 
the  serum  is  washed  from  the  blood  before  adding 
the  micro-organisms,  practically  no  bacteria  are 
ingested.  This  shows  the  importance  of  the  serum, 
but  does  not  differentiate  between  some  effect  on 
the  leucocytes,  on  the  one  hand,  or  the  bacteria. 
on  the  other.  3.  In  order  to  decide  this  point  one 
may  subject  the  suspension  of  bacteria  to  the 
action  of  fresh  cell-free  serum,  and  after  a  contact 
of  about  30  minutes  remove  all  the  serum  by  cen- 
trifugation,  and  mix  the  '^sensitized^'  culture  with 
serum-free   blood ;  phagocytosis   occurs   almost  to 


TECHNW.  325 

the  same  degree  as  when  the  fresh  defibrinated 
blood,  containing  serum,  is  used.  These  results 
seem  to  show  definitely  that  phagocytosis  depends 
on  the  power  of  the  opsonins  to  affect  the  bacteria 
in  some  peculiar  manner. 

Later  experiments  showed  that  the  opsonic  opsonic 
power  of  the  blood  varied  in  the  course  of  disease 
just  as  is  found  in  the  case  of  other  immune  sub- 
stances. The  relation  of  such  an  abnormal  opsonic 
power  to  that  of  normal  serum  was  designated  as 
the  opsonic  index. 

The  AYright  technic  deals  with  three  factors  as    Teciinic. 
will  be  apparent  from  the  above :  leucocytes,  bac- 
teria and  serum. 

Leucocytes. — The  leucoc3'tes  are  obtained  in  dif- 
ferent ways  according  to  the  kind  employed.  Human 
leucocytes  are  obtained  by  puncturing  the  lobe  of 
the  ear  or  tip  of  the  finger  with  a  small  lancet 
and  catching  the  blood  in  a  1  to  1.5  per  cent, 
solution  of  sodium  citrate  in  0.85  per  cent,  sodium 
chlorid  solution.  The  amount  of  blood  necessary 
is  usually  small,  about  1  c.c.  and  10  c.c.  of  citrate 
solution  is  required  to  keep  the  blood  from  clot- 
ting. By  centrifugalizing,  the  corpuscles  are 
separated  from  the  citrate  solution  and  the  cor- 
puscles washed  by  pipetting  of  the  supernatant 
fluid  and  replacing  it  with  physiologic  salt  solu- 
tion. Two  such  washings  are  made  and  then  the 
pearly-colored  blood  cream  containing  the  leuco- 
cytes is  removed  from  the  surface  of  the  red  cells 
for  use. 

Serum. — This  is  obtained  as  for  agglutination 
or  other  tests. 


326  INFECTION     AND     IMMUNITY. 

Bacteria. — The  bacteria  are  obtained  by  growing 
on  the  surface  of  an  agar  slant  for  from  12  to  24 
hours;  they  are  then  removed  into  salt  solution 
either  by  means  of  a  loop  or  by  adding  the  salt 
solution  directly  to  the  agar  slant.  The  concen- 
tration should  be  such  that  a  smear  on  a  slide 
shows  plenty  of  bacteria  to  the  field  of  the  micro- 
scope while  at  the  same  time  the  individual  organ- 
isms are  well  separated  from  one  another.  Fre- 
quently to  obtain  such  a  mixture  it  is  necessary 
to  shake  the  emulsion  thoroughly  to  insure  divi- 
sion of  clumps. 

Having  the  above  constituents  they  are  mixed 
together  in  the  following  way: 

A  capillary  tube  is  made  by  drawing  out  a  glass 
tube  of  about  4  mm.  caliber  and  a  length  of  about 
16  cm.  A  small  volume  of  serum  is  allowed  to 
run  into  the  tube  by  capillary  attraction  and  the 
length  of-  the  volume  marked  on  the  outside  of 
the  tube.  A  small  air  bubble  about  1  mm.  in 
length  is  then  drawn  into  the  tube  and  then  a  vol- 
ume of  bacterial  suspension  equal  to  the  volume 
of  serum.  Again  a  small  bubble  of  air  is  drawn 
into  the  tube  and  lastly  a  volume  of  leucocyte  mix- 
ture equal  to  those  of  serum  and  bacteria. 

The  three  constituents  are  then  mixed  together 
by  drawing  the  three  up  into  the  large  part  of 
the  tube  and  mixing  together  there  by  drawing 
back  and  forth  or  they  may  be  mixed  on  a  glass 
slide  and  then  drawn  back  into  the  capillary  tube. 
The  mixture  is  then  incubated  the  desired  length 
of  time  (usually  about  15  minutes)  and  smeared 
on  a  slide  as  in  making  an  ordinary  blood  smear. 


TECHNIC.  327 

The  slide  is  then  stained  with  an  appropriate 
stain  (for  most  bacteria  one  of  the  eosinates  of 
methylene  blue)  and  examined  with  the  immer- 
sion lens  of  a  microscope. 

The  number  of  bacteria  in  successive  leucocytes 
is  counted  and  an  average  made.  Various  figures 
are  given  as  the  necessary  number  of  leucocytes 
which  should  be  counted  to  give  accurate  results. 
The  number,  however,  should  be  governed  by  the 
uniformity  of  the  numbers  of  bacteria  in  succes- 
sive leucocytes.  If,  for  instance,  the  average 
number  of  bacteria  in  three  successive  counts  of 
ten  leucocytes  is  nearly  the  same,  it  is  more  ac- 
curate to  take  such  an  average  than  if  more  leuco- 
cytes are  counted  with  no  uniformity  of  numbers. 

The  ratio  of  the  average  number  of  bacteria  to 
the  leucocyte  taken  up  in  the  presence  of  a  given 
serum  to  the  average  number  taken  up  in  the 
presence  of  a  serum  taken  as  normal  is  the  opsonic 
index. 

By  the  immunization  of  animals  by  various  immune 
bacteria  and  other  cells  a  serum  of  high  opsonic 
power  may  be  produced.  The  opsonic  action  of 
such  serums,  in  contrast  to  that  of  normal  serum, 
is  not  destroyed  by  heating  to  56°  C.  and  differs 
from  normal  opsonin  in  other  respects  which  will 
be  discussed  later.  In  immunizing  animals  with 
typhoid  bacilli,  it  was  noticed  that  the  estimation 
of  the  concentration  of  opsonin  in  the  typhoid  im- 
mune serum  by  the  Wright  method  of  comparison 
did  not  show  results  that  w^ould  be  expected.  That 
is,  a  highly  immune  animal  would  show  little 
difference  from  one  with  low  immunity.  Klien, 
therefore,  estimated  the  opsonic  power  by  determ- 


Opsonins. 


328  JXFECTION     AXD     IMMUNITY. 

ining  the  dilution  point  at  which  the  number  of 
bacteria  taken  up  by  the  leucocytes  equals  the 
number  taken  up  without  the  presence  of  serum. 
This  dilution  point  is  sometimes  called  the  point 
of  opsonic  extinction.  The  phagocytosis  taking 
place  without  the  influence  of  serum  is  known  as 
spontaneous  phagocytosis. 
Specificity  of  There  has  been  considerable  conflict  of  opinion 
as  to  whether  there  are  specific  opsonins  in  normal 
serum  for  different  varieties  of  cells  or  one  opsonic 
substance  capable  of  acting  on  a  variety  of  cells. 
Hektoen  concludes  from  his  own  studies  and  those 
of  others^  consisting  of  specific  absorption  experi- 
ments and  observations  on  the  specific  fall  in 
opsonic  power  following  injection  of  specific  anti- 
gen, and  from  other  experiments,  that  normal 
serum  contains  specific  opsonins  which  are  capable 
of  specific  absorption  and  which  are  the  same 
substances  which  are  increased  to  form  the  im- 
mune opsonin. 

The  immune  opsonins  are  easily  demonstrated 
by  absorption  experiments  to  be  highly  specific. 

Hektoen  and  Euediger  have  shown  that  normal 
opsonins  are  almost  completely  destroyed  or  inacti- 
vated by  heat  and  are  therefore  thermolabile.  The 
inactive  opsonin  (opsonoid)  by  saturating  the 
receptors  of  bacteria  with  the  haptophore  group 
prevents  further  sensitization  with  fresh  serum. 

These  investigators  also  show  that  opsonin  may 
be  bound  or  neutralized  similarly  to  complement 
by  solutions  of  various  salts. 

The  nature  of  immune  opsonins  has  been  the 
subject  of  much  discussion.  As  was  stated  before, 
immune  opsonins  resist  a  temperature  of  from  56 


NATURE     OF     OPSONIN.  329 

to  60 "^  C.  Dean,  Cowie  and  Chapin,  and  others 
have  shown,  however,  that  the  opsonic  power  of 
heated  serum  may  be  increased  by  the  addition  of 
normal  serum  similar  to  that  reactivation  taking 
place  on  adding  complement  to  amboceptor. 
Browning  has  pointed  out  that  this  apparent  sim- 
ilarity of  the  action  of  normal  serum  on  heated 
opsonin  may  be  due  to  summation  of  effects.  He 
has  shown  that  by  separating  immune  body  in 
opsonic  serum  at  0°  C.  by  saturation  with  bacteria 
and  then  adding  complement  there  is  a  true  activ- 
ation, and  that  no  such  action  occurred  in  treating 
the  bacteria  with  complement,  washing  and  then 
adding  heated  opsonic  serum.  He  concludes  that 
immune  body  and  complement  may  be  concerned 
in  opsonic  action,  but  leaves  open  the  question  of 
whether  the  immune  body  is  the  thermostabile 
opsonin  or  not. 

Hektoen  concludes  from  the  following  facts  that   opsonins  aa 
opsonins  are  distinct  from  other  antibodies.  Antibodies. 

1.  Heat  may  almost  completely  destroy  the 
opsonic  power  of  serum  leaving  the  lytic  ambo- 
ceptors intact. 

2.  Serum,  normal  as  well  as  immune,  may  con- 
tain opsonin  for  a  given  organism  but  not,  at  least 
so  far  as  is  known,  the  proper  lytic  amboceptor  for 
that  organism. 

3.  A  serum  may  contain  opsonin  for  an  organ- 
ism, but  no  agglutinin  and  the  opsonin  may  persist 
after  destruction  of  bacteriolytic  complement  by 
heat. 

4.  In  immunization  lytic  and  opsonic  powers  do 
not  run  parallel. 


330  INFECTION     AND     IMMUNITY. 

Relation  to  If  an  animal  is  injected  with  a  proper  dose  of 
Processed,  bacteria  or  alien  red  cells,  there  results  as  a  rule 
in  the  first  day  or  so  a  fall  in  the  opsonic  content 
of  the  blood  along  with  other  antibodies.  This 
period  is  known  as  the  "negative  phase,"  and  is 
followed  by  a  steady  rise  which  reaches  its  height 
from  the  eighth  to  the  twelfth  day  and  gradually 
falls  to  normal.  The  negative  phase  as  pointed 
out  by  Hekto'en  is  specific  and  it  has  not  been 
determined  whether  it  is  due  to  a  specific  absorp- 
tion or  to  an  effect  on  the  antibody  producing 
cells. 

"In  several  acute  infectious  diseases  the  course 
of  the  formation  of  new  opsonin  for  the  infecting 
agent,  in  the  typical  attack,  terminating  promptly 
in  recovery  without  complications,  shows  a  marked 
general  resemblance  to  the  opsonin  and  antibody 
curve  after  a  single  antigen  injection  in  the 
normal  animal;  it  also  bears  definite  and  constant 
relations  to  the  clinical  phenomena.  During  the 
early  stages  when  the  symptoms  are  pronounced 
there  is  a  negative  phase  and  then  as  the  symptoms 
begin  to  subside  the  opsonin  curve  rises  above 
normal,  reaching  the  highest  point  several  days 
after  the  onset,  followed  by  a  gradual  subsidence. 
This  is  true  of  the  pneumococcus  opsonin  in  pneu- 
monia, of  the  opsonin  for  the  diphtheria  bacillus 
in  diphtheria,  of  the  streptococcus  opsonin  in 
erysipelas,  and  also  of  the  opsonin  for  the  dip- 
lococcus  of  mumps  in  that  disease.  The  curve  is 
typical  also  for  the  streptococcus  in  scarlet  fever, 
indicating  clearly  that  this  organism  unquestion- 
ably plays  a  definite  role  in  scarlet  fever,  whatever 
its  actual  causative  relation  to  the  disease  may  be. 


IMPORTANCE     OF    OPSONINS.  331 

In  pneumonia  the  greatest  rise  in  the  lencocytosis 
appears  to  precede  somewhat  the  highest  rise  of 
the  opsonin.  In  all  these  diseases  the  typical 
wave-like  opsonin  curve  is  modified  by  the  devel- 
opment of  complications  of  various  kinds  and  at 
the  onset  of  which  it  commonly  undergoes  a  dis- 
tinct depression.  In  rapidly  fatal  cases^  for  in- 
stance of  pneumonia,  the  opsonic  curve  or  index 
may  not  return  from  the  primary  depression,  but 
sink  lower  and  lower.  In  prolonged  infections, 
general  as  well  as  local,  there  occur  irregular 
fluctuations  and  in  chronic,  more  or  less  stationary 
cases,  the  opsonic  index  is  often  subnormal.  At 
this  time  further  details  cannot  be  given.  My 
chief  point  is  to  m^ake  clear  the  close  association 
between  recovery  and  the  wave-like  rise  of  the 
opsonin,  and,  as  a  result  of  the  immunization  in 
all  likelihood  also  of  other  antibodies,  in  the 
typical  attack  of  acute  so-called  self-limited  in- 
fections. In  some  of  the  diseases  the  opsonin  is 
the  only  antibody  that  we  can  measure  readily 
with  our  present  means.  As  I  have  stated,  an 
intraphagocytic  destruction  of  pneumococci  and 
streptococci  takes  place  in  the  presence  of  fresh 
leucocytes  and  opsonic  serum,  whereas  either  alone 
constitutes  a  good  medium  for  these  bacteria. 
Taking  these  facts  into  account  it  seems  to  me 
that  the  wave-like  course  of  the  opsonin  in  pneu- 
monia and  in  acute  streptococcus  infections  is  a 
strong  point  on  the  side  of  the  signal  importance 
of  phagocytosis  in  their  healing,  whatever  other 
measure,  of  which  at  present  Ave  know  less  or 
nothing,  may  be  in  operation  also."^ 

1.  Ilektoen  :    Opsonins  and  Othei-  Antibodies,  Science,  1909. 


332 


INFECTION     AND     IMMUNITY 


Interaction       As  pointed  out  bv  Gljnn  and  Cox,  the  work  of 

Lencocytes    Wright  and  his  followers  has  resulted  in  an  nndue 

and  opson-   ^Qgi^^,^  of  ^|-^g  importance  of  the  variation  in  the 

power  of  leucoc3^tosis  in  the  leucocytes  themselves 
as  a  factor  in  phagocytosis.  They  emphasize  the 
fact  that  while  the  determination  of  opsonic  power 
may  be  an  indication  of  the  degree  of  immunity, 
it  does  not  represent  the  phagocytic  power  of  the 
blood  as  a  whole.  In  order  to  ascertain  the 
valuation  of  the  different  components  separately 
and  as  a  whole  they  suggest  the  comparison  of  the 
leucocytes  of  the  blood  in  question  with  those  of 
normal  blood  and  call  the  ratio  of  the  first  to  the 
second  the  cytophagic  index.  Secondly,  they  com- 
pare the  action  of  the  leucocytes  and  the  serum 
of  the  blood  in  question  with  the  action  of  normal 
leucocytes  and  serum.  The  ratio  of  the  first  to 
the  second  is  called  the  opsonocytophagic  index. 
What  has  come  to  be  known  as  the  hypothesis 
of  Welch  is  of  such  practical  and  theoretical  im- 
portance that  reference  to  it  should  not  be  passed 
over.  It  may  be  put  in  the  form  of  the  following 
question:  If  bacterial  toxins  and  the  constituents 
of  bacterial  cells  so  act  on  the  tissue  cells  that  the 
latter  produce  bodies  (antibodies)  which  are  in- 
imical to  the  bacteria,  why  may  not  the  body  fluids 
in  turn  so  act  on  the  bacteria  that  the  latter  pro- 
duce bodies  (antibodies)  which  are  inimical  to  the 
tissue  cells?  "Looked  at  from  the  point  of  view 
of  the  bacterium,  as  well  as  from  that  of  the 
animal  host,  according  to  the  hypothesis  advanced, 
the  struggle  between  the  bacteria  and  the  body 
cells  in  infections  may  be  conceived  as  an  im- 
munizing  contest   in   which   each    participant   is 


Hypothesis 
of  Welcli. 


HYPOTHESIS  OF   WELCH.  333 

stimulated  by  its  opponent  to  the  production  of 
cytotoxins  hostile  to  the  other,  and  thereby  en- 
deavors to  make  itself  immune  against  its  an- 
tagonist/^  (Welch.) 

A  more  reasonable  hypothesis  could  hardly  be 
advanced,  and  no  small  number  of  facts  known 
at  the  present  time  are  in  harmony  with  it. 
Walker  had-  already  performed  work  of  a  funda- 
mental character,  which  showed  that  the  typhoid 
bacillus,  when  grown  in  the  presence  of  its  anti- 
serum^ acquires  greater  virulence  for  animals. 
Furthermore,  a  greater  dose  of  protective  serum 
was  required  to  save  guinea-pigs  from  infection 
with  the  immunized  culture  than  from  the  same 
strain  which  had  not  been  immunized.  The  fact 
has  been  known  for  a  long  time  that  the  typhoid 
bacillus  resists  agglutination  when  freshly  cul- 
tivated from  a  patient  having  the  disease,  whereas 
it  becomes  easily  agglutinable  after  a  period  of 
artificial  cultivation.  It  may  well  be  assumed  that 
the  bacillus,  when  playing  the  part  of  an  infecting 
organism,  gradually  was  immunized  against  the 
agglutinating  properties  of  the  ]Datient's  serum; 
and,  on  the  other  hand,  that  it  lost  this  resistance 
after  it  had  been  removed  from  the  stimulating 
influence  of  the  infected  body.  This  immuniza- 
tion with  agglutinins  may  be  carried  on  in  the 
test  glass,  and  bacteria  which  have  been  so  treated 
acquire  the  power  to  absorb  a  greater  quantity  of 
agglutinin  from  the  homologous  serum   (Bail). 

Another  pertinent  observation  was  that  by 
Wechsberg,  who  found  that  a  strain  of  the  diph- 
theria bacillus  when  grown  in  a  medium  contain- 
ing diphtheria   antitoxin  could  be  made  to  pro,- 


334  IXFECTIOy     AND     IMMUMTY. 

duce  diphtheria  toxin  more  abiindantl3\  We  may 
assume  that  the  antitoxin  combined  with  the  cor- 
responding receptors  situated  in  the  bacilli  (diph- 
theria toxin),  and  that  the  bacilli  were,  as  a  result, 
stimulated  to  produce  a  greater  number  of  such 
receptors  (toxin). 

Consistent  as  these  observations  are  with  the 
hypothesis  under  discussion,  Welch  meant  a  great 
deal  more  than  the  immunization  of  the  bacteria 
against  the  defensive  powers  of  the  animal  body. 
Not  only  may  a  bacterium  during  infection  become 
more  resistant  to  the  bactericidal  action  of  the 
body  by  producing  antibodies  for  those  bactericidal 
agencies,  or  by  its  ability  to  absorb  and  dispose  of 
a  greater  quantity  of  bacteriolysin ;  and  not  only 
may  a  bacterium  be  able  to  respond  to  the  presence 
of  natural  antitoxins  in  the  body  by  the  produc- 
tion of  more  toxin;  but,  in  addition,  certain  con- 
stituents of  our  body  fluids  may,  by  combining 
with  suitable  bacterial  receptors,  stimulate  the 
bacterium  to  the  production  of  a  whole  shower  of 
cytotoxins,  which  attack  the  leukocytes,  erythro- 
cytes, nerve  cells,  liver,  kidney,  etc.  The  nature 
of  the  animal  substances  which  may  combine  with 
the  bacterial  receptors  and  thus  cause  the  forma- 
tion of  the  bacteriogenic  cytotoxins  is  left  an  open 
question,  and  is  not  of  essential  importance  for 
the  theory;  it  is  not  at  all  necessary  that  they  be 
toxic  for  the  bacterium,  and  they  may  even  be 
taken  up  as  food  substances.  Likewise  the  possible 
nature  of  the  cytotoxins  produced  by  the  bacterium 
is  of  secondary  importance.  It  so  happened  that 
Welch  assumed  that  they  might  be  of  the  nature 
of  amboceptors,  which  may  become  complemented 


HYPOTHESIS  OF   WELCH.  335 

by  bacterial  complement^  by  the  circulating  com- 
plement of  the  body  or  by  endocomplements  of 
the  tissue  cells.  One  could  with  equal  reasonable- 
ness assume  that  they  may  be  complete  toxins, 
receptors  of  the  second  order,  with  a  haptophorous 
and  a  toxophorous  structure. 

A  well-known  statement  of  Metchnikoff  is  to 
the  effect  that  a  particular  bacterium  when  viru- 
lent is  not  so  readily  taken  up  by  leucocytes  as  is 
an  avirulent  strain.  This  fact  has  been  noted  re- 
peatedly in  recent  times  in  the  study  of  phagocy- 
tosis in  the  test  tube.  This  may  be  because  the 
organism,  in  its  virulent  parasitic  state,  secretes 
substances  which  repel  the  phagocytes,  neutralize 
the  opsonins,  or  because  of  the  formation  of  actual 
leucocytic  toxins. 

One  of  the  most  widely  known  phenomena  in 
relation  to  the  virulence  of  some  organisms  is  that 
their  pathogenicity  may  be  increased  by  passing 
them  through  suitable  animals  repeatedly.  The 
best  results  are  obtained  when  intermediate  arti- 
ficial cultivation  is  avoided  and  the  inoculations 
are  made  directly  from  the  dead  into  the  living 
animal.  It  may,  with  all  reason,  be  assumed  that 
by  continued  residence  in  the  host  the  bacterium 
has  been  trained  to  produce  a  greater  quantity  of 
toxic  substances  which  are  inimical  to  the  host, 
and  that  the  increased  virulence  of  the  parasite 
depends  on  this  condition. 

Although  up  to  the  present  time  systematic 
attempts  to  place  the  hypothesis  of  Welch  on  a 
firm  experimental  basis  appear  not  to  have  been 
made,   the   observations   cited,   as   well   as   others 


336  INFECTION     AND     IMMUNITY. 

which   could  be   enumerated,   provide   cumulative 
evidence  of  its  correctness. 

AGGEESSINS 

Aggressins.  Xot  entirely  foreign  to  the  subject  discussed 
above  is  the  so-called  aggressin  theory  of  Bail,  the 
essential  points  of  which  may  be  given  without 
entering  into  a  detailed  discussion. 

Bail  attributes  to  pathogenic  bacteria  the  prop- 
erty of  "aggressiveness/'  through  which  they 
directly  antagonize  the  protective  agencies  of  the 
body.  The  micro-organisms  of  highest  parasitic 
powers,  the  "true  parasites,"  as  those  belonging  to 
the  hemorrhagic  septicemia  group,  possess  the 
greatest  aggressiveness,  since  they  are  able  to  pro- 
liferate in  the  blood  stream  Avhile  the  antibacterial 
activities  of  the  body  (phagocytosis,  etc.)  are  held 
in  abeyance.  Other  bacteria,  which  in  causing 
disease  tend  to  remain  localized,  and,  if  by  any 
means  they  reach  the  blood  stream,  are  not  able 
to  proliferate  greatly  in  this  place,  are  "half 
parasites"  and  have  a  lower  degree  of  aggressive- 
ness; they  are  more  susceptible  to  phagocytosis 
and  to  the  action  of  bacteriolysins  (typhoid, 
cholera,  d3'Sentery).  Saprophytes  have  no  aggres- 
sive action. 

This  is  very  general,  but  Bail  and  his  co-workers 
have  attempted  to  put  the  conception  on  an  experi- 
mental basis  by  demonstrating  the  existence  of  a 
substance  on  which  the  aggressi^'eness  of  bacteria 
depends;  to  this  substance  they  give  the  name  of 
"aggressin." 

Intraperitoneal  inoculation  of  the  tubercle  bacil- 
lus   into   the    guinea-pig   leads    to   more    or   less 


AGGRESSINS.  337 

general  tuberculosis  and  to  the  death  of  the  animal 
in  the  course  of  a  few  weeks.  If,  during  the 
course  of  the  disease,  a  second  injection  of  a  large 
quantity  of  the  bacillus  is  made  into  the  peritoneal 
cavity,  or  if  an  injection  of  tuberculin  is  given, 
the  animal  dies  very  quickly.  This  is,  of  course, 
nothing  more  than  the  well-known  hypersuscep- 
tibility  of  tuberculous  animals  to  the  products  of 
the  tubercle  bacillus.  In  addition  to  this  fact, 
however,  a  similar  result  was  obtained  in  another 
manner.  If  a  large  quantity  of  bacilli  is  placed 
in  the  peritoneal  cavity  of  a  healthy  guinea-pig, 
and  the  exudate  is  removed  after  twenty-four  hours 
and  freed  from  leucocytes  and  bacilli,  the  aggressin 
of  the  bacillus  is  said  to  be  present  in  the  clear 
fluid.  This  is  demonstrated  by  injecting  some  of 
the  fluid,  together  with  tubercle  bacilli,  into  the 
peritoneal  cavity  of  another  healthy  guinea-pig 
The  rapid  death  of  the  animal  is  the  result, 
whereas  the  bacilli  alone  cause  death  only  after  a 
long  period,  and  the  cell-free  exudate  alone  is 
without  toxicity. 

A  similar  condition  has  been  found  in  experi- 
mental infections  with  a  number  of  bacteria 
(typhoid,  cholera,  dysentery^  plague,  chicken  cho- 
lera), the  essential  fact  being  the  same:  that,  fol- 
lowing intraperitoneal  or  intrapleural  inoculation, 
the  resulting  exudate,  when  freed  from  leukocytes 
and  bacteria,  has  the  power  of  intensifying  an  in- 
fection by  the  corresponding  organism. 

There  seems  at  present  to  be  no  definite  knowl- 
edge concerning  the  nature  of  these  aggressins,  al- 
though Bail  thinks  they  may  resemble  true  toxins 
in  some  respects.     Likewise  the  precise  character 


338  INFECTION     AND     IMMUNITY. 

of  their  action  is  unknown,  although  Bail  and  his 
co-workers  are  strongly  inclined  to  the  view  that 
they  inhibit  phagocytosis  by  some  direct  action  of 
the  leucocytes. 

It  is  further  interesting  that  immunization  with 
aggressins  is  said  to  give  rise  to  the  formation  of 
antiaggressins,  and  that  by  the  use  of  antiaggres- 
sive  serum  the  action  of  the  aggressins  is  neutral- 
ized, and  the  bacteria  consequently  become  the 
prey  of  the  leucocytes.  The  action  of  the  anti- 
aggressive  serum  is  said  not  to  depend  on  the  pres- 
ence of  bacteriolysins. 

Proof  of  the  non-identity  of  the  aggressins  of 
Bail  and  the  toxins  produced  by  the  organism 
has  not  been  very  convincing. 
viruiin.  Investigating  the  resistance  of  virulent  pneu- 
mococci  (which  vary  greatly  from  non-virulent 
forms)  to  phagocytosis,  Eosenow  was  able,  by  au- 
tolysis in  salt  solution,  to  extract  the  substance 
on  which  this  resistance  depends.  He  was  not 
only  in  this  way  able  to  render  them  phagocytable, 
but  also  by  treating  non-virulent  strains  with  this 
extract  he  was  able  to  render  them  more  virulent 
and  resistant  to  phagocytosis. 

The  substance  which  he  calls  viruiin  is  insoluble 
in  alcohol  and  ether,  and  is  thermostable. 


CHAPTEE  XXI. 


THE  SIDE-CHAIN"  THEORY  OF  EHRLICH  AND  ITS 

RELATION"  TO  THE  THEORY  OF 

PHAGOCYTOSIS. 

In  1885,  before  the  discovery  of  toxins  and  anti-   side-ciiain 

^  "^  Theory    Ap- 

toxins  and  before  there  was  any  knowledge  as  to  piled  to 
the  real  nature  of  immunity,  Ehrlich^  published  a 
small  volume  on  the  ^'Oxygen  Eequirements  of  the 
Body.^^  Herein  the  belief  was  expressed  that  the 
assimilation  of  foods  by  cells  is  accomplished  only 
after  chemical  union  has  taken  place  between  the 
food  substance  and  some  constituent  of  cellular 
protoplasm.  It  is  not  the  understanding  that  as- 
similation is  at  an  end,  however,  when  this  union 
has  occurred,  for  certain  molecules  of  complex 
chemical  nature  and  of  great  size  must  be  split  up 
into  simpler  substances  before  they  can  enter  into 
the  composition  of  protoplasm.  Therefore,  the  cell 
constituent  which  combines  with  the  nutritious 
molecule  serves  only  as  a  link  to  bring  the  food- 
stuff into  relation  with  the  digestive,  oxidizing  or 
fermentative  activities  of  the  cell. 

Ehrlich  speaks  of  that  portion  of  living  proto-  "Leistungs- 

■'•  ^  .    .   7  kern"    and 

plasm  which  represents  the  cellular  activities  as  side-Chains. 
the  ''LeistungsJcern''  of  the  cell,  the  center  of  cel- 
lular activity,  or  the  central  group  of  the  proto- 
plasm, whereas  those  chemical  groups  which  bind 
the  food  substances  are  called  the  side-chains  of  the 
''LeistungsJcern/' 

The  author  of  the  theory  has  made  his  concep- 

1.  Ueber  das  Sauerstoffbediirfnis  des  Organismus. 


340  INFECTION     AND     IMMUNITY. 

tion  more  tangible  through  an  analogy  which  was 
drawn  with  the  so-called  ring  or  nuclens  of  benzol 
and  its  side-chains.  The  molecule  of  benzol,  CgHj,, 
has  a  definite  formation  in  which  each  carbon 
atom  is  linked  to  two  others  in  such  a  manner  as 
to  form  a  ring;  three  valences  of  each  carbon 
atom  are  satisfied  in  this  way,  and  the  fourth  is 
satisfied  by  atoms  of  hydrogen,  one  of  which  is  at- 
tached to  each  carbon  atom,  thus : 

H 

I 
C 

H-C        C-H 

II         I 

H-C        C— H 

\    // 

C 

I 

H 

This  ring  is  analogous  to  the  "Leistungshern"  of 
the  cell.  A  great  variety  of  chemical  compounds 
exists  and  very  many  may  be  produced  syntheti- 
cally by  substituting  for  one  or  more  atoms  of 
hydrogen,  one  or  more  other  groups  of  atoms  which 
may  be  very  simple  or  very  complex.  The  groups 
which  have  been  substituted  are  called  side-chains. 
Thus  benzoic  acid  is  formed  from  benzol  by  sub- 
stituting the  acid  radical  COOH  for  a  particular 
H,  and  the  COOH  in  this  instance  is  a  side-chain 
of  the  ring : 

o 

c 

I 

c 
/  <^ 

H-C        C-H 

II  I 

H-C       C— H 

\  // 

C 


SIDE-CHAINS.  341 

Just  as  the  side-chains  of  the  "Leistungslcern'' 
may  combine  with  food  particles,  so  may  the  side- 
chains  of  the  benzol  ring  combine  with  other 
groups  of  atoms  and  thereby  assimilate  the  latter, 
so  to  say,  into  the  ring.  To  choose  a  simple  exam- 
ple, the  sodium  of  sodium  hydroxid  may  unite  with 
the  side-chain  CO  OH  to  form  sodium  benzoate, 
the  hydrogen  of  the  acid  radical  being  replaced  by 
the  sodium,  thus : 

o 

// 
c 

C 

/   -^ 

H-C        C-H 

li         I 
H— C        C-H 

C 


Presumably  it  is  in  some  such  manner  as  sodium 
is  brought  into  relationship  with  the  benzol  nu- 
cleus, in  the  example  cited,  that  the  food  sub- 
stances are  brought  into  relationship  with  the 
^'LeistungsJcern^  of  the  cell. 

The  hypothesis  of  Ehrlich  carries  with  it  the  Haptopiiores. 
assumption  that  the  side-chains  of  a  cell  possess  or 
consist  of  definite  groups  of  atoms  capable  of  unit- 
ing chemically  with  certain  other  definite  groups 
of  atoms  in  the  food  particles;  hence  both  the  side- 
chain  and  the  food  substance  have  combining 
groups — haptophores.  The  side-chains  of  the  cells 
Ehrlich  now  calls  receptors,  elements  which  we 
have  already  recognized  in  connection  with  im- 
munity. Inasmuch  as  different  foods  have  differ- 
ent chemical  compositions,  it  is  likely  that  their 
binding  groups  are  not  identical;  and  if  this  be 


342  INFECTION     AND     IMMUNITY. 

true  there  nrnst  exist  many  kinds  of  receptors  each 
of  which  is  ahle  to  unite  only  with  that  food  sub- 
stance which  has  a  corresponding  binding  group  of 
atoms. 

In  contrast  to  the  condition  with  respect  to 
foods,  it  is  held  that  chemical  substances  of  known 
composition,  drugs  and  alkaloids  never  become  in- 
corporated as  a  part  of  the  protoplasm,  that  is, 
they  do  not  unite  with  cell  receptors,  although 
they  may  affect  the  vitality  and  function  of  proto- 
plasm profoundly.  Their  inability  to  jdeld  anti- 
bodies as  a  result  of  immunization  is  supposed  to 
depend  on  this  condition.  Such  substances,  ac- 
cording to  Ehrlich,  exist  in  the  cell  in  a  condition 
of  unstable  salt  formation  with  some  constituent 
of  the  protoplasm,  or  in  a  state  of  solid  solution. 

The  following  statement  from  a  recent  publica- 
tion b}''  Ehrlich  summarizes  the  nutritional  aspect 
of  the  theory:  "We  must  assume  that  all  sub- 
stancts  which  enter  into  the  structure  of  proto- 
plasm are  fixed  chemically  by  the  protoplasm.  We 
have  always  distinguished  between  assimilable  sub- 
stances which  serve  for  nutrition  and  which  enter 
into  permanent  imion  with  the  protoplasm,  and 
those  which  are  foreign  to  the  body.  No  one  be- 
lieves that  quinin  and  similar  substances  are  as- 
similated, that  is,  enter  into  the  composition  of  the 
protoplasm.  On  the  other  hand,  the  food  sub- 
stances are  bound  in  the  cells,  and  this  union  must 
be  considered  as  chemical.  One  can  not  extract  a 
sugar  residuum  from  cells  with  water,  but  must 
first  split  it  off  with  acids  in  order  to  set  it  free. 
But  now  such  a  chemical  union,  like  every  syn- 
thesis,   demands    the    presence    of    two    binding 


tilDE-VllMS    THEORY   OF  IMMUNITY 


343 


groups  of  maxima]  chemical  affmity,  which  are 
suited  one  to  the  other.  The  binding  groups  which 
reside  in  the  cells  and  which  bind  food  substances 
I  designate  as  side-chains  or  receptors,  while  T 
have  called  those  of  the  molecules  of  foodstuffs  the 
haptophorous  groups.  I  also  assume  that  proto- 
plasm is  endowed  with  a  large  series  of  such  side- 
chains,  which  through  their  chemical  constitution 
are  able  to  bind  the  different  foodstuffs  and  there- 
by provide  the  prerequisite  for  cellular  metabol- 
ism." 

If  the  side-chain  theory  of  nutrition  is  to  be- 
come the  side-chain  theory  of  immunity  it  is  nec- 
essary that  it  undergo  elaboration  in  order  that  the 
formation  of  antibodies  may  be  adequately  ex- 
plained. If,  as  Ehrlich  assumes,  the  union  of 
toxin  with  cell  receptors  causes  the  overproduction 
of  the  latter  as  antitoxin,  and  if  this  imion  is  an- 
alagous  to  that  of  food  substances  with  similar  re- 
ceptors, one  may  wonder  that  antibodies  are  not 
formed  for  our  ordinary  foods,  antibodies  which 
would  be  discharged  from  the  cells  and  which 
would  unite  with  circulating  nutritious  particles 
and  thereby  bring  about  a  condition  of  starvation. 
Without  entering  into  the  intricacies  of  this  ques- 
tion, it  seems  probable  that  normally  a  condition 
of  physiologic  equilibrium  exists  between  the  food 
substances  on  the  one  hand  and  the  cellular  activi- 
ties on  the  other,  so  that  the  union  of  food  with 
protoplasm  constitutes  no  abnormal  stimulus  to 
the  ''Leistungshern'  of  the  cell.  When,  however, 
cells  are  diverted  from  their  normal  metabolic 
function  by  union  with  toxin?  and  other  "abnormal 
food    substances."   the   effect   on    the   cell   is   de- 


Side-Chain 
Theory  Ap- 
plied  to 
Immunity. 


344  INFECTION     AND     IMMUNITY. 

I 

scribed  as  a  cell  defect,  the  defect  consisting  of  the 

functional  elimination  of  the  receptor.  The  "Leis- 
tungs'kern'  as  the  vital  or  regulating  center  of  the 
cell  repairs  the  defect  by  the  formation  of  new  re- 
ceptors, and  in  harmony  with  the  hypothesis  of 
Weigert  produces  not  only  enough  to  repair  the 
defect,  but  a  great  excess,  with  the  result  that 
many  are  thrown  into  the  circulation.  The  anal- 
ogy of  the  "Leistungshern'  with  the  benzol  ring 
can  not  be  carried  to  this  extent,  for  the  latter  has 
no  power  of  reproducing  side-chains  to  take  the 
place  of  one  which  has  been  bound  by  some  new 
group  of  atoms. 
Bsseutiai       It  will  be  appropriate  in  this  place  to  consider 

Tenets    of  ±  i       x  x 

Eiiriicii's  the  character  of  the  proof  which  has  been  offered 
in  support  of  the  three  tenets  which  constitute  the 
framework  of  the  theory  of  Ehrlich.  These  three 
tenets  may  be  expressed  as  follows:  1.  Antitox- 
ins counteract  toxins  by  entering  into  chemical 
union  with  them;  a  similar . union  takes  place  be- 
tween other  antibodies  and  their  homologous  sub- 
stances. 2.  Toxins  in  injuring  cells  combine 
chemically  with  a  definite  constituent  of  the  proto- 
plasm, the  cell  receptor;  other  antigenous  sub- 
stances- enter  into  similar  union  with  the  appro- 
priate receptors  of  cells.  3.  The  specific  antibodies 
of  the  serum  are  new-formed  receptors  identical  in 
structure  with  those  which,  as  cell  constituents, 
had  combined  with  the  homologous  antigens. 

Chemical       First  tcuct  I    In  the  early  days  of  studies  on  im- 

Antibo'dies  muuity  (1890-1897),  the  action  of  a  toxin  and  the 

^*       sens"  efficacy  of  an  antitoxin  could  be  determined  only 

2.  An  antigen  or  an   antigenous  substance  Is  one  which 
Is  able  to  cause  the  formation  of  an  antibody. 


UNION  OF  ANTIBODIES  WITH  ANTIGENS.  345 

by  injecting  these  substances  into  living  animals, 
and  the  animal  experiment  naturally  continues  to 
be  the  means  of  testing  the  curative  and  prophy- 
lactic values  of  serums.  So  long,  however,  as'  such 
experiments  vi^ere  performed  exclusively  in  the  liv- 
ing animal  the  nature  of  the  action  of  antitoxin 
remained  to  a  certain  extent  in  doubt.  It  re- 
mained uncertain  whether  antitoxin  is  protective 
because  it  actually  destroys  the  toxin,  because  neu- 
tralization of  a  chemical  nature  occurs,  or  because 
in  some  manner  it  increases  the  resistance  of  the 
inoculated  animal.  In  Chapter  XII  experiments 
were  cited  to  show  that  antitoxin  does  not  destroy 
the  toxin,  and  this  is  generally  admitted  to-day. 
There  continues  to  be  some  difference  of  opin- 
ion, however,  in  relation  to  the  two  other  possibili- 
ties, i.  e.,  as  to  whether  antitoxin  combines  chemi- 
cally with  toxin,  or  is  efficacious  because  of  its 
stimulating  power  on  the  tissues  of  the  animal. 
Behring,  the  discoverer  of  antitoxin,  was  from  the 
beginning  an  exponent  of  the  chemical  theory,  even 
at  a  time  when  the  conceptions  of  Ehrlich  had  not 
been  fully  developed.  On  the  other  hand,  certain 
noted  investigators,  especially  Eoux  and  Buchner, 
and  later  Metchnikoff,  stood  for  the  alternative 
view. 

Following  closely  on  Behring's  great  discovery, 
Ehrlich  studied  the  hemagglutinating  toxin  ricin, 
from  the  castor-oil  bean,  and  by  immunization 
mth  it  produced  a  specific  antitoxin,  i.  e.,  anti- 
ricin.  Eicin  is  toxic  to  erythrocj^es  both  in  the 
animal  body  and  in  the  test-tube,  and  if  it  could 
be  shown  that  antiricin  protects  in  the  test-tube 
by  a  direct  effect  on  the  toxin,  it  was  highly  prob- 


Ricin   and 
Antiricin. 


of   Toxins   by 
Antitoxins. 


346  INFECTION     AND     IMMUNITY. 

able  that  its  action  in  the  animal  body  would  be  of 
a  similar  nature.  The  results  left  no  doubt  in  the 
mind  of  Ehrlich  that  antiricin  unites  chemically 
with  ricin,  and  the  applicability  of  this  principle 
in  animal  experiments  became  all  the  more  ap- 
parent when  it  was  shown  that  the  proportion  of 
antiricin  which  protects  in  vitro  also  protects  in 
vivo.  It  is  held  that  similar  proof  of  chemical  union 
between  bacterial  hemolysins,  the  hemolysin  of 
venom  and  the  leucocidin  of  the  staphylococcus 
with  their  respective  antitoxins  is  equally  valid. 
ciiemicai  Na-  Although  the  animal  body  can  not  be  dispensed 
Neutralization  witli  in  tcstiug  the  actiou  of  the  antitoxins  of 
diphtheria  and  tetanus,  certain  principles  of  chem- 
ical action  are  found  to  prevail  which  leave  no 
doubt  in  regard  to  the  chemical  neutralization  of 
the  toxins.  If  neutralizing  proportions  of  diph- 
theria toxin  and  antitoxin  be  mixed  in  a  test-tube 
and  injected  immediately,  the  serum  does  not  af- 
ford absolute  protection;  if,  however,  the  mixture 
is  allowed  to  stand  for  from  fifteen  to  twenty  min- 
utes before  injection,  the  protection  is  absolute. 
This  alone  would  point  to  an  action  of  the  anti- 
toxin on  the  toxin,  for  the  completion  of  which  a 
certain  amount  of  time  is  required.  For  the  com- 
plete neutralization  of  tetanus  toxin  by  its  anti- 
toxin about  forty  minutes  are  necessary  at  ordinary 
temperatures.  Then  certain  other  chemical  princi- 
ples described  in  Chapter  XII,  are  found  to  hold 
true :  That  neutralization  proceeds  more  rapidly 
at  higher  than  at  lower  temperatures,  more  rapidly 
in  concentrated  than  in  dilute  solutions,  and  that 
it  takes  place  in  accordance  with  the  law  of  mul- 
tiple proportions. 


UNION  OF  ANTIBODIES  WITH  ANTIGENS.  347 


Granting,  then,  that  neutralization  of  toxin  by 
antitoxin  is  of  a  chemical  nature,  the  first  essential 
step  in  the  chemical  or  side-chain  theory  is  estab- 
lished. If  antitoxin  combines  chemically  with 
toxin,  union  must  occur  through  combining  groups 
which  each  molecule  possesses.  Herein  lies  the  ex- 
perimental justification  for  assuming  the  existence 
of  haptophorous  groups. 

The  situation  is  more  difficult  in  regard  to  the 
union  of  receptors  of  the  second  and  third  orders, 
i.  e.,  agglutinins  and  amboceptors  with  the  ho- 
mologous receptors  of  bacteria  and  other  cells. 
One  can  not  titrate  bacteria  against  agglutinin  or 
bactericidal  amboceptors  so  exactly  as  toxin  can  be 
titrated  against  antitoxin,  for,  in  the  first  place, 
it  is  difficult  to  obtain  at  will  a  desired  concentra- 
tion of  bacteria  and  to  keep  it  without  alteration, 
and,  in  the  second  place,  bacterial  cells  contain 
many  more  receptors  than  are  necessary  for  their 
agglutination  and  solution.  A  given  mass  of  bac- 
teria will  take  up  varying  quantities  of  agglutinin, 
depending  on  the  concentration  of  the  latter,  and 
the  same  principle  applies  to  the  absorption  of 
bactericidal  and  hemolytic  amboceptors.  As  more 
and  more  agglutinin  is  added,  the  total  araoimt 
absorbed  increases  with  each  addition,  although 
the  ratio  of  absorbed  to  unabsorbed  agglutinin 
grows  less  continuously.  The  conditions  which 
govern  this  phenomenon  are  not  understood. 
Perhaps  no  condition  speaks  more  decisively  for 
chemical  union  of  these  bodies  with  cell  receptors 
than  immunization  experiments  which  were  car- 
ried on  with  cells  which  had  been  treated  with  a 
great  excess  of  the  specific  antiserum.     The  as- 


Union   of  Agr- 
glntinin  and 
Amljoceptor 
with   Cell 
Receptors. 


348  INFECTION     AND     IMMUNITY. 

sumption  was  made  tliat  if  one  could  force  all  the 
receptors  of  erj'throcytes,  for  example,  to  take  up 
the  specific  amboceptors,  such  corpuscles  should 
lose  their  power  to  cause  the  formation  of  a  hemo- 
lytic serum  when  injected  into  a  suitable  animal. 
This  would  follow  logically,  for  the  receptors  of 
the  corpuscles,  being  already  bound,  would  not  be 
free  to  unite  with  receptors  of  the  immunized  ani- 
mal. Antibodies  were  not  formed  under  these  cir- 
cumstances, from  which  it  is  concluded  that  the 
receptors  of  the  erythrocytes  had  united  chemi- 
cally with  the  antibodies  of  the  serum  (Sachs). 
In  order  to  completely  occupy  all  the  receptors  of 
the  vibrio  of  cholera  Pfeiffer  used  3,000,000  to 
4,000,000  times  the  dissolving  amount  of  the  anti- 
cholera  serum.  Although  the  mere  absorption  of 
agglutinins  and  amboceptors  by  the  homologous 
cells  is  cited  in  favor  of  the  chemical  hypothesis, 
we  may  bear  in  mind  the  contention  of  certain  in- 
vestigators that  this  absorption  is  physical  rather 
than  chemical. 
Chemical  \a-  Sccoud  tcuct :  What  evidcucc  have  we  that  tox- 
^tf'r^^***  Union    jj^g   qj^([  other  antififenous   substances   enter   into 

of  Toxins  and  o 

Other  Anti-  chcmical  uuion  with  receptors  in  the  cells  of  the 
Cell  Recep-  immunized  animal?  It  is  probable  that  no  ob- 
servation speaks  more  strongly  in  favor  of  such 
union  than  a  famous  experiment  of  Wassermann's 
in  which  the  central  nervous  sj^stem  of  guinea- 
pigs  was  ground  up  with  tetanus  toxin,  the  mix- 
ture allowed  to  stand  for  a  short  time  and  then 
injected  into  mice.  The  mixture  was  found  to  be 
non-toxic,  and  further  experiments  showed  that 
the  neutralizing  power  resides  in  the  solid  tissue 
in  the  emulsion.     It  is  claimed  by  Ehrlich  that 


tors 


ANTIGEN  AND  CELL  RECEPTORS.  349 

this  experiment  demonstrates  positively  that 
chemical  union  of  tetanus  toxin  takes  place  with 
constituents  of  the  nervous  tissue.  The  toxin  hav- 
ing been  completely  neutralized  can  not  again  be 
extracted  from  the  tissue.  The  condition  is  the 
opposite  in  relation  to  some  poisonous  alkaloids, 
as  strychnin,  which  it  appears  does  not  combine 
with  the  protoplasm  firmly  and  may  again  be  ex- 
tracted by  simple  methods. 

Von  Dungern  conducted  very  important  work 
with  the  precipitins,  which  is  interpreted  as  show- 
ing that  albuminous  substances  other  than  toxins 
are  taken  up  chemically  by  the  cells.  He  injected 
considerable  quantities  of  a  foreign  serum  into  the 
veins  of  rabbits  and  studied  its  disappearance  from 
the  blood  of  the  injected  animal.  Traces  of  the 
foreign  serum  could  be  recognized  by  treating  the 
rabbit  serum  with  a  specific  precipitin  for  the  for- " 
mer,  the  precipitin  having  been  obtained  pre- 
viously by  the  immunization  of  other  animals. 
The  foreign  serum  disappeared  from  the  circula- 
tion of  the  rabbit  with  some  rapidity  and  since  it 
could  not  be  demonstrated  in  the  excretions,  it 
seemed  necessary  to  assume  that  it  had  been  bound 
by  the  cells,  that  is  to  say,  by  the  cell  receptors. 

Third  tenet:  Is  there  any  direct  experimental  Proliferation 
proof  that  those  constituents  of  cells  which  have 
been  designated  as  cell  receptors  actually  undergo 
multiplication  in  the  cell  itself  as  a  preliminary  to 
their  discharge  into  the  circulation  in  the  form  of 
antibodies?  If  this  condition  could  be  demon- 
strated in  one  instance,  one  might  reasonably  con- 
sider that  it  typifies  a  law  according  to  which  all 
antibodies   are  formed.     Further  experiments  by 


350  INFECTION     AND     IMMUNITY. 

von  Dungern  with  the  precipitins  seem  to  show 
that  such  intracellular  overproduction  actually 
does  occur.  The  experiments  concern  the  fate  of 
"Majaplasma'^  (plasma  of  the  spider-crab)  when 
injected  into  the  circulation  of  the  rabbit  (see 
above).  If  a  single  injection  of  the  serum  is 
given,  a  specific  precipitin  for  the  latter  body  in 
due  time  may  be  demonstrated  in  the  serum  of  the 
rabbit.  Eventually  the  precipitin  disappears  from 
the  circulation  by  excretion  or  other  means.  At 
that  time,  when  all  the  precipitin  has  disappeared, 
one  may  assume  that  the  cells  of  the  animal  still 
contain  an  increased  number  of  precipitin  recep- 
tors, although  the  latter  are  no  longer  produced  to 
such  an  extent  that  they  are  thrown  into  the  cir- 
culation. If  this  condition  exists  the  tissues  of 
the  animal  at  this  time  should  be  able  to  absorb  a 
larger  amount  of  the  foreign  serum,  given  in  a  sec- 
ond injection,  and  perhaps  absorb  it  more  rapidly 
than  the  tissues  of  an  untreated  rabbit.  Using  a 
specific  precipitating  serum  in  order  to  detect 
traces  of  the  foreign  serum  which  still  remained  in 
the  blood  of  the  injected  animal,  von  Dungern  de- 
termined that  its  tissues  actually  do  absorb  the 
plasma  more  rapidly  than  do  the  tissues  of  the 
untreated  rabbit.  The  cells  of  the  former  have  a 
greater  absorbing  power,  i.  e.,  a  greater  binding 
power  for  the  plasma;  therefore,  an  increased 
number  of  receptors. 

These  examples  are,  perhaps,  sufficient  to  illus- 
trate the  principles  of  experimentation  which  have 
been  followed  in  the  attempt  to  obtain  definite 
proof  of  the  correctness  of  the  essential  points  of 
the  theory.    The  results  are  in  entire  accord  with 


RECEPTORS.  351 

the  primary  assumptions  and  show  that  the  theory 
continues  to  serve  as  an  explanatory  basis  for 
newly-discovered  facts,  and  as  a  foundation  on 
which  new  researches  may  be  instituted. 

In  addition  to  the  three  main  principles  treated   other  iinpor- 

^  ^  tant    Pnn- 

of  above,  the  following  points  are  necessarily  in-   cipies  of 
eluded  in  a  summary  of  the  views  of  Ehrlich,  many 
facts  of  a  corroborative  nature  having  been  ascer- 
tained in  independent  laboratories. 

1.  The  recognition  of  different  types  of  tissue 
receptors  by  which  peculiarities  in  the  action  of  the 
different  antibodies  are  explained.  Eeceptors  of 
the  first  order,  as  antitoxins,  anticomplements  and 
antiamboceptors,  are  regarded  as  relatively  simple 
bodies  because  no  other  constituent  can  be  recog- 
nized than  the  haptophorous  group  by  which  they 
combine  with  their  homologous  substances.  Ee- 
ceptors of  the  second  order  are  more  complicated 
in  that  they  have  something  more  than  the  mere 
binding  power;  usually  they  are  able  to  produce 
some  observable  change  in  the  substance  with 
which  they  unite.  Hence,  each  has  a  toxophorous 
or  a  z}TXLotoxic  group  in  addition  to  the  hapto- 
phorous, and  the  two  groups  are  part  of  the  same 
molecule.  Toxins,  agglutinins,  precipitins  and 
complements  are  receptors  of  the  second  order. 
Receptors  of  the  third  order,  i.  e.,  the  bacterio- 
lytic, hemolytic  and  cytotoxic  amboceptors,  are 
still  more  complex  in  that  they  are,  so  to  say,  only 
partial  antibodies,  the  complete  body  consisting  of 
the  amboceptor-complement  complex.  The  ambo- 
ceptor is  not  an  active  body,  but  serves  as  an  in- 
termediary body  to  connect  the  active  substance, 
complement,  with  the  cell.     In  the  cytolytic  proc- 


352  INFECTION     AND     IMMUNITY. 

ess  the  amboceptor  through  its  cytophilous  hapto- 
phore  first  iinites  with  the  cell^  and  as  a  result 
acquires  an  increased  affinity  for  complement, 
with  which  it  unites  through  its  complemento- 
philous  haptophore.  Only  after  this  double  union 
is  completed  may  complement  affect  the  cell. 
From  this  it  follows  that  complement  in  the  cyto- 
lytic process  does  not  combine  with  the  cell  di- 
rectly. As  previously  stated,  Bordet  and  others 
oppose  the  idea  that  the  absorption  of  these  bodies 
is  of  a  chemical  nature,  considering  it  rather  to  be 
a  physical  process. 

Ehrlich  has  intimated  his  belief  that  tissue  am- 
boceptors play  the  chief  role  in  the  fixation  of 
foods  by  the  cells  of  the  body. 

2.  The  chemical  theory  explains  the  specificity 
which  characterizes  the  formation  and  action  of 
antibodies.  Every  antigen  has  a  haptophore  which 
is  different  from  those  of  other  antigens;  conse- 
quently, it  unites  only  with  the  corresponding  cell 
receptor,  and  the  latter  when  overproduced  and 
cast  into  the  circulation  retains  its  specific  binding 
power  for  the  corresponding  antigen. 

3.  The  multitude  of  antibodies  which  have  been 
obtained  indicate  that  the  cells  contain  a  vast 
number  of  different  receptors  which  correspond  to 
the  three  types  now  recognized ;  that  is,  there  is  a 
different  antitoxin  receptor  for  every  kind  of 
toxin,  etc. 

4.  Ehrlich  has  limited  the  application  of  the 
term  toxin  to  those  substances  of  animal  or  plant 
ori^nn,  immunization  with  which  causes  the  forma- 
tion  of  specific  antitoxins.  Other  characteristics 
have  been  given  in  Chapter  XI. 


RECEPTORS.  353 

5.  Eeceptors  of  the  second  order,  toxins,  agglu- 
tinins, precipitins  and  complements,  undergo'  a 
peculiar  degenerative  change,  spontaneously  or  as 
a  result  of  exposure  to  injurious  agents,  in  which 
the  toxophorous  or  zymotoxic  group  disappears  or 
is  rendered  inactive.  The  termination  -oid  is  af- 
fixed to  the  altered  bodies,  as  toxoid,  agglutinoid, 
precipitoid  and  complementoid.  Wechsberg  has 
described  a  similar  degeneration  of  one  of  the  hap- 
tophores  of  amboceptors,  calling  the  product  am- 
boceptoid.  Toxoids  and  complementoids  on  im- 
munization cause  the  formation  of  corresponding 
antitoxins  and  anticomplements,  by  virtue  of  re- 
tention of  their  haptophorous  groups. 

6.  By  means  of  a  special  technic  devised  for 
studying  the  neutralization  of  toxin  by  antitoxin, 
i.  e.,  the  partial  saturation  method,  Ehrlich  found 
diphtheria  toxin  to  be  a  very  complex  substance. 
Not  all  the  molecules  of  the  toxin  have  the  same 
affinity  for  antitoxin,  and  according  to  the  de- 
grees of  their  affinity  have  received  the  names  of 
prototoxin,  deuterotoxin  and  tritotoxin.  Simi- 
larly, protoxoids  and  s3rQtoxoids  are  molecules  of 
toxoid  having  different  affinities  for  antitoxin. 
These  conditions  are  represented  graphically  by 
means  of  the  "toxin  spectrum"  described  pre- 
viously. 

7.  Ehrlich  claims  that  the  diphtheria  bacillus 
secretes  two  toxins,  one  of  which  causes  the  acute 
manifestations  of  diphtheritic  intoxication,  where- 
as the  second  toxin,  i.  e.,  toxon,  has  a  prolons^ed 
incubation  period  and  probably  causes  diphtheritic 
paralysis.  Toxon  has  a  lower  affinity  for  diph- 
theria antitoxin  than  the  other  constituents  of  the 


354  INFECTION     AND     IM31UNITY. 

toxin  solution,  but  is  neutralized  by  the  same  anti- 
toxin. This  view  is  strongly  opposed  by  Arrhe- 
nius  and  Madsen,  who,  working  on  the  basis  that 
the  neutralization  of  toxin  takes  place  according 
to  certain  laws  of  physical  chemistry,  claim  that 
toxon  is  nothing  more  than  toxin  which  has  disso- 
ciated from  the  toxin-antitoxin  molecule. 

8.  It   is    thought    that    the   incubation    period 
•  which  characterizes  the  action  of  toxins  represents 

to  a  large  degree  the  time  required  for  the  action 
of  the  toxophorous  group  after  the  toxin  has  been 
bound  by  the  cells. 

9.  Ehrlich  stands  for  the  multiplicity  of  com- 
plements in  opposition  to  Bordet  and  others  who 
claim  the  existence  of  but  one  complement 
(alexin).  The  various  complements  differ  in  the 
nature  of  their  haptophores,  without  regard  to 
possil)le  differences  in  their  zymotoxic  groups. 

10.  Only  those  organs  which  have  suitable  re- 
ceptors may  produce  an  antibody  for  a  given  anti- 
gen, i.  e.,  only  those  cells  which  may  enter  into 
chemical  combination  with  the  antigen.  It  does 
not  follow,  however,  tliat  only  those  organs  which 
show  clinical  or  anatomic  lesions  may  produce, 
say,  an  antitoxin;  for  other  organs  not  so  suscep- 
tible to  the  action  of  the  toxin  may  still  possess 
the  suitable  receptors  and  cast  them  out  as  anti- 
toxin. 

CauNes    of       The  various  types  of  immunity  are  explainable 
TypeH*'of  oTi  the  basis  of  the  side-chain  theory  in  the  follow- 

Immnnity.    ^^„   tcrmS  ! 

1.  Natural  immunity  to  toxins  may  depend  on 
(a)  a  lack  of  suitable  cell  receptors,  the  toxin  con- 
sequently finding  no  point  of  attack;  (b)  a  vei7 


NATURE     OF    IMMUNITY.  355 

low  affinity  between  cell  receptors  and  toxin  so 
that  the  latter  does  not  unite  with  the  cells  except 
under  special  conditions  (e.  g.,  the  immunity  of 
chicken  to  tetanus)  ;  or  (c)  on  the  presence  of 
natural  antitoxins. 

3.  Acquired  active  antitoxic  immunity  depends 
on  the  multiplication  and  excretion  of  cell  recep- 
tors (antitoxin)  into  the  circulation,  the  new- 
form.ed  bodies  having  the  power  of  combining 
chemically  with  additional  toxin  which  may  be  in- 
troduced. 

3.  Passive  antitoxic  immunity,  as  established  by 
the  injection  of  an  antitoxin,  depends  on  the  abil- 
ity of  the  antitoxin  to  combine  chemically  with  the 
toxin  and  thus  to  divert  the  latter  from  the  cells. 

4.  Natural  immunity  to  bacteria  depends  on  (a) 
a  lack  of  suitable  cell  receptors  with  which  the 
toxic  bacterial  constituents  might  combine;  (b)  a 
very  low  affinity  between  cell  receptors  and  the 
toxic  bacterial  constituents;  or  (c)  on  the  presence 
of  natural  bacteriol3^sins  (amboceptors  and  com- 
plements). 

5.  Acquired  active  antibacterial  immunity  de- 
pends on  the  multiplication  and  excretion  into  the 
circulation  of  specific  cell  receptors  (amboceptors) 
which  have  the  power  of  uniting  with  complement 
to  Idll  the  micro-organisms  which  may  be  intro- 
duced. 

6.  Passive  antibacterial  immunity,  as  estab- 
lished by  the  injection  of  a  bacteriolytic  serum, 
depends  on  the  ability  of  the  amboceptors  con- 
tained in  the  serum  to  unite  chemically  with  the 
receptors  of  the  micro-organism,  as  a  result  of 
.which  complement  is  absorbed  to  kill  and  perhaps 


356  INFECTION     AND     IMMUNITY. 

to  dissolve  the  bacteria.    The  complement  maj  be 
present  in  the  serum  which  is  injected,  or  the  nat- 
ural complement  of  the  individual  may  be  utilized 
by  the  amboceptors. 
Comparison       When  oue  sccks  to  compare  the  theory  of  Ehrlich 

of    Theories         .  . 

of   Ehriicii   with  that  of  Metchnikoff,  one  finds  little  more  in 

nnd     Metcli-  ii  j^i  i  /•  i    •     • 

nikofl.  common  than  the  general  purpose  of  explaining 
the  phenomena  of  immunity.  Yet  it  is  remark- 
able that  where  there  is  so  little  in  common  there 
are  so  few  contradictions  of  an  essential  nature. 

The  theory  of  Ehrlich  has  that  degree  of  defi- 
niteness  which  it  must  have  in  order  to  be  a  plausi- 
ble chemical  theory,  whereas  that  of  Metchnikoff 
seems  more  general  in  that  it  is  so  largely  biologic 
and  vitalistic. 

Each  has  a  certain  relation  to  nutrition.  Phago- 
cytosis as  a  nutritional  measure  is  found  in  lower 
t3'pes  of  animals,  and  accomplishes  nothing  further 
than  to  bring  the  food  substance  in  contact  with 
the  digestive  ferments  contained  in  the  cell.  In 
relation  to  nutrition  the  theory  of  Ehrlich  begins, 
so  to  say,  where  the  phagocytic  theory  leaves  off, 
involving,  as  it  does,  the  method  by  which  food 
substances  become  a  part  of  the  protoplasm. 

Metchnikoff,  with  Ehrlich,  recognizes  the  vari- 
ous antibodies  which  have  been  discovered.  The 
former  holds  that  all  are  produced  by  the  phago- 
cytes without  suggesting  clearly  a  method  by 
which  they  may  be  formed.  Ehrlich  assumes  a 
very  precise  method  by  which  they  may  be  formed, 
but  designates  no  particular  cells  as  their  pro- 
ducers, stating  only  in  a  general  way  that  an  anti- 
body is  produced  only  by  those  cells  with  which  the 


THEORIES     OF     METCHNIKOFF.  367 

antigen  may  combine;  in  some  instances,  the  leu- 
cocytes may  be  such  cells. 

The  theory  of  Metchnikoff  is  not  concerned  with 
the  structure  of  toxins  and  the  various  antibodies, 
nor  with  the  method  by  which  toxins  may  injure 
tlie  cells,  whereas  Ehrlich  presents  definite  concep- 
tions on  these  points. 

Both  recognize  that  there  is  more  than  one  com- 
plement (cytase).  Ehrlich  recognizes  no  limit  to 
the  varieties  which  may  exist,  whereas  Metchnikoff 
describes  but  two  cytases,  microcytase  and  macro- 
cytase. 

The  view  which  Metchnikoff  has  expressed,  that 
antitoxin  is  produced  by  some  action  of  the  phago- 
cytes on  the  toxin,  is  directly  opposed  to  that  of 
Ehrlich  which  recognizes  antitoxin  as  a  product  of 
the  cell  itself. 

They  agree  that  amboceptors  (fixators)  become 
extracellular  in  the  blood. 

Metchnikoff  holds  that  complements  (cytases) 
are  produced  only  by  the  phagocytes  and  that 
these  substances  are  found  in  the  plasma  or  serum 
only  as  a  result  of  injury  to  the  phagocytes  (phago- 
lysis).  These  points  are  not  involved  essentially 
in  the  theory  of  Ehrlich.  Certain  investigators 
who  work  in  harmony  with  the  side-chain  theory, 
as  well  as  those  who  represent  the  views  of  Metch- 
nikoff, have  extracted  complement  from  the  leuco- 
cytes. Some  of  Ehrlich's  supporters  believe  that 
complement  exists  normally  in  the  plasma. 

Metchnikoff  and  Ehrlich  hold  divergent  views 
concerning  the  action  of  antitoxins,  the  former  be- 
lieving that  antitoxins  stimulate  the  phagoc}i;es  to 
an  increased  absorption  and  consequent  destruc- 


358  IXFECTIOy     AXD     IMMUNITY. 

tion  of  the  toxin^  whereas  Ehrlich  claims  that 
antitoxin  neutralizes  toxin  by  combining  chemi- 
cally with  it. 

According  to  Metchnikoff,  all  types  of  immunity 
depend,  directly  or  indirectly,  on  phagoc3rtic  activ- 
ity. While  the  side-chain  theory  is  not  in  har- 
mony with  such  a  broad  assumption,  it  carries 
with  it  no  denial  of  the  phenomenon  of  phagocyto- 
sis nor  of  its  importance  in  certain  infections. 
Compatibility  From  tlicsc  selcctcd  Considerations  it  is  seen 
that  the  two  theories  do  not  stand  to  each  other  in 
the  relation  of  antitheses,  and  in  the  light  of  pres- 
ent knowledge  it  would  seem  unwarranted  to  cling 
to  one  view  to  the  absolute  exclusion  of  the  other. 
It  does  not  follow  that  because  demonstrable 
serum  properties  explain  immunity  to  one  disease, 
or  to  a  certain  group  of  diseases,  that  recovery 
from  all  diseases  must  depend  on  properties  of  the 
serum;  nor  because  phagoc3^tic  activity  explains 
recovery  in  certain  instances  that  recovery  from 
all  diseases  must  depend  on  a  similar  activity.  The 
conditions  which  exist  in  each  disease,  of  course, 
must  be  recognized  independently.  It  so  happens 
that  recovery  from  a  certain  group  of  diseases, 
e.  g.,  staphylococcus,  streptococcus  and  pneumo- 
coccus  iafections,  is  not  accompanied  by  the  de- 
velopment of  conspicuous  antitoxic  or  bactericidal 
properties  in  the  serum,  but  they  are  characterized 
by  a  great  increase  in  the  number  of  circulating 
leucocytes  (microphages),  cells  of  Imown  phago- 
cytic and  bactericidal  power,  whereas  the  opposite 
conditions  are  found  in  certain  other  diseases,  e. 
g.,  typhoid  and  diphtheria.  If  one  seeks  the  most 
apparent  explanation  in  each  case,  the  great  leuco- 


OP-S'O.Y/A'aS'    and    EHRLiaWS    THEORY.       359 

c3'tosis  Avoiild  seem  to  be  of  prime  importance  in 
the  first  group,  and  the  antitoxic  and  bactericidal 
power  of  the  serum  in  the  second. 

Investigations  from  various  sources  render  un-  opsonins. 
questionable  the  value  of  phagocytosis  in  certain 
infections,  and  of  particular  significance  is  the 
work  concerning  opsonins  which  was  referred  to  in 
the  preceding  chapter.  From  this  work  it  follows 
that  even  for  the  phagoc}i:ic  destruction  of  bac- 
teria the  serum  contains  properties  which  are  of 
essential  importance.  This  appears  of  all  the  more 
importance  from  the  fact  that  immunization  with 
at  least  some  micro-organisms  (streptococcus, 
staph3dococcus)  causes  an  increase  in  opsonins  or 
bacteriotropic  substances. 

The  accompanying  illustration,  with  some  modi- 
fications, is  taken  from  ^'Ehrlich's  SeitenJcetten- 
theorie/'  by  Ludvig  Aschoff.  The  cell  used  for 
immunization  is  assumed  to  be  a  cell  which  will 
cause  the  formation  of  antitoxin,  agglutinin  or 
precipitin,  and  bactericidal  amboceptors;  the 
diphtheria  bacillus  is  such  an  organism,  consider- 
ing toxin  as  one  of  the  receptors  of  the  bacillus. 
This  means  that  the  bacillus  is  able  to  cause  the 
overproduction  of  all  three  types  of  receptors.  The 
illustration,  however,  is  on  the  basis  of  a  h}T)0- 
thetical  cell  (p.  360). 

A  list  of  immunizing  bodies,  their  anti-bodies, 
and  s}Tionyms  for  complement  and  amboceptor, 
is  also  appended  (p.  361). 


IMMUNIZATION    WITH   ANTIBODIES. 


361 


List  of  Immunizing  Bodies  and  Their  Antibodies. 


Antigens  or 
Immnnizing 
substances. 

Toxins. 
Complements 

Ferments. 

Precipitogen- 
o  u  s  s  u  b  - 
stances 

Agglutinogen- 
o  u  s  s  u  b  - 
stances 

Opsonigenous 
substances 
of  bacteria 

Cytotoxin  pro- 
ducing sub- 
stances 


Products  of 
i  mmuniza- 
tion. 

Antitoxins. 
A  n  t  i  c  o  m  ple- 

ments 
Antiferments 
Precipitins 


Agglutinins 
Opsonins 
Cytotoxins. . 


'Hemolysins 
Bacteriolysins 
Special    Cyto- 
toxins 
Spermotoxin 
Nephrotoxin 
Hepatotoxin 
Neurotoxin 
Syncytioly- 
sin,  etc. 


Consisting  o  f 
two  bodies, 
i.  e.,  comple- 
me  n  t  and 
amboceptor. 


Immunization  with  Antibodies. 


Precipitins 
Agglutinins 
Cytotoxins 

Hemolysins, 

etc. 


Complement 


Antiprecipitins 
Antiagglutinins  (°?) 
Anticytotoxins 

Antihemolysins, 

etc. 


r  Consisting  either  of  anti- 

I  complements  or  antiam- 

i  boceptors  ;  the    latter 

J  may  be  an  antibody  for 

\  the  complementophilous 

I  or    for    the    cytophilous 

I  haptophore  of  the  ambo- 

V  ceptor. 


Alexin 
Cytase 


Synonyms 

Amboceptor 

Immunkorper 

Zwischenkorper 

Intermediary  body 

Substance  sensibilisatrice 

Fixator 

Preparator 

Copula 

Desmon 


CHAPTEK   XXII. 


PRINCIPLES   OF   SEROTHERAPY, 

In  the  strict  sense  serotherapy  means  the  in- 
jection of  antitoxic  or  antibacterial  serums  for 
curative  or  prophylactic  purposes;  this  is  passive 
immunization  or  direct  serotherapy.  Active  im- 
munization, in  which  the  tissues  vl  the  individ- 
ual are  induced  to  form  antitoxins  or  antibacterial 
substances  as  a  result  of  vaccination  or  protective 
inoculations,  may  be  considered  as  indirect  sero- 
therapy. We  may,  therefore,  include  tho  latter  as 
one  of  the  serotherapeutic  measures. 

Bearing  in  mind  the  significance  of  the  terms 
active  and  passive  immunization,  and  the  fact 
that  they  may  be  used  for  curative  and  prophylac- 
tic purposes,  the  various  procedures  may  be  classi- 
fied as  follows:* 

I.       PROPHYLACTIC    INJECTIONS. 

ciasNificatiou  A.  Activc  immunization,  in  which  vaccina- 
apeutic'^MeaN-  tiou  and  protcctivc  inoculations  are  included,  as 
with  the  organisms  of  typhoid,  cholera  and  plague. 
Depending  on  the  material  injected,  the  result  is 
the  formation  of  antitoxins  or  antimicrobic  sub- 
stances (amboceptors)  ;  agglutinins  are  formed  in- 
cidentally. 

1.  Inoculation  of  virulent  organisms,  (a)  In- 
oculation with  small  amounts  of  a  virulent  organ- 
ism, i.  e.,  of  a  non-fatal  dose;  used  principally  in 
experimental  work.     (&)  Inoculation  with  virulent 

•  ModiJ5ed     from     Deutsch     and     Feistmantel     in     "Die 
Impfstoffe    und    Heilsera,"    Leipsic.     Geo.    Thleme,  1903. 


nres. 


SEROTHERAPEUTIC  MEASURES.  363 

organisms  into  a  tissne  which  has  some  natural  re- 
sistance. The  success  of  vaccination  against  small- 
pox by  using  virus  obtained  directly  from  the  dis- 
eased, a  method  which  was  practiced  in  earlier 
times,  was  probably  due  to  the  fact  that  the  virus 
found  unfavorable  conditions  for  the  development 
of  virulence  in  the  skin.  In  some  instances  im- 
munization is  accomplished  more  succcGsfully  by 
inoculation  of  bacteria  or  toxins  into  the  blood 
stream,  as  in  Kitt's  method  of  vaccination  against 
symptomatic  anthrax  and  in  immunization  with 
rattlesnake  venom. 

2.  Injection  of  attenuated  virus  or  toxin.  At- 
tenuation may  be  accomplished  by  air  and  light 
(chicken-cholera,  Pasteur)  ;  by  cultivation  at  high 
temperatures  (anthrax,  Pasteur)  ;  by  chemical 
agents  (anthrax,  Eoux;  diphtheria  and  tetanus 
toxins,  Behring  and  Eoux)  ;  by  desiccation  (rabies, 
Pasteur)  ;  by  passing  the  virus  through  other 
animals  (swine  er^^sipelas,  Pasteur).  This  last 
observation  was  a  most  instructive  one;  passing 
the  bacillus  through  the  rabbit  several  times  in- 
creased its  virulence  for  the  rabbit  but  decreased  it 
for  swine,  while  passing  the  organism  through  the 
dove  increased  its  virulence  for  swine. 

3.  Injection  of  killed  organisms  (anthrax,  Tous- 
saint;  swine  plague,  Salmon  and  Smith).  This 
is  the  safest  means  of  vaccinating  against  cholera, 
typhoid  and  plague.  In  the  Pasteur  treatment  of 
hydrophobia  the  first  injection  of  the  dried  spinal 
cord  probably  contains  the  killed  virus. 

4.  Injection  of  bacterial  constituents  (a)  Bacter- 
ial cell  plasm  (Buchner's  plasmin,  obtained  by  sub- 
mitting micro-organisms  to  high  pressure,  and 
Koch's    tuberculin    TPi)  ;    (b)    Soluble    bacterial 


364  INFECTION     AND     IMMUNITY. 

products  (the  bacterial  proteins,  as  Koch's  old 
tuberclin  and  mallein;  the  soluble  toxins; 
products  of  bacterial  autolysis).  AVlien  toxins 
are  injected  antitoxins  are  formed.  The 
autolytic  products  of  some  organisms,  e.  g., 
typhoid  and  dysentery,  cause  the  formation  of  bac- 
tericidal amboceptors  and  agglutinins,  but  not 
antitoxins. 

B.  Passive  immunization:  the  prophylactic  in- 
jection of  antibacterial  and  antitoxic  serums, 

C.  Mixed  active  and  passive  immunization:  the 
simultaneous  injection  of  an  immune  serum  with 
the  corresponding  organism,  which  may  be  killed 
or  living.  The  serum  causes  immediate,  though 
temporary,  resistance,  and,  in  the  meantime,  an 
active,  more  permanent  immunity  develops  as  a 
consequence  of  the  injection  of  the  organ.'sms. 
This  method  has  been  practiced  with  swine  plague, 
swine  erysipelas,  rinderpest,  and  experimentally 
in  typhoid,  cholera  and  plague. 

II.      CURATIVE   INJECTIONS. 

A.  Active  immunization. 

1.  Injection  of  killed  micro-organisms  in  small 
doses  with  the  intention  of  hastening  antibody  for- 
mation, as  suggested  by  Fraenkel  in  the  treatment 
of  typhoid  fever ;  value  not  yet  demonstrated. 

B.  Passive  immunization. 

1.  With  antitoxic  serums:  diphtheria,  tetanus, 
snake  bites,  plague,  tuberculosis  (?),  typhoid  (?), 
streptococcus  infections  (?),  etc. 

2.  With  antibacterial  serums:  typhoid,  cholera, 
plague,  dysentery,  streptococcus  (?),  staphylococ- 
cus (?)  and  pneumococcus  (?)  infections. 


STRENGTH  OF  SERUMS. 


365 


In  general,  serums  to  be  effective  must  have  a 
certain  strength.  When  diphtheria  antitoxin  was 
first  used  preparations  were  put  on  the  market 
which  contained  twenty  or  fewer  antitoxin  units 
per  cubic  centimeter,  a  strength  which  would 
necessitate  the  injection  of  150  c.c.  or  more  in  or- 
der to  introduce  3,000  units.  Much  of  the  early 
criticism  of  diphtheria  antitoxin  is  traceable  to  the 
low  value  of  the  serums  used  at  that  time  rather 
than  to  an  injurious  effect  on  the  patients.  If 
diphtheria  antitoxin  now  contains  less  than  250 
units  per  c.c.  it  is  considered  unfit  for  use;  many 
serimis  contain  500  or  more  units  per  cubic  cen- 
timeter. 

Antitoxic  and  other  serums  should  be  free  from 
micro-organisms  and  toxins.  The  cases  of  tetanus 
which  developed  in  St.  Louis  following  the  injec- 
tion of  diphtheria  antitoxin  will  be  remembered. 
With  correct  governmental  supervision  of  the 
manufacture  of  serums,  such  accidents  are  entirely 
preventable.^ 

For  the  sake  of  simplicity  we  may  consider  the 
principles  involved  in  serum  therapy  under  the 
three  topics  of  (a)  antitoxins,  (b)  bactericidal  or 
antibacterial  serums,  and  (c)  vaccination. 

(a)  antitoxins. 

It  has  been  sufficiently  emphasized  that  neutral- 
ization of  toxin  by  antitoxin  implies  a  chemical 
union  between  the  two  substances.  When  the  two 
are  mixed  outside  the  body  at  a  given  temperature 
and  at  a  given  concentration,  the  rapidity  and  com- 
pleteness with  which  the  union  occurs  depends 
only  on  the  degree  of  affinity  which  one  has  for  the 


General 
.Strength  of 
Serums. 


Antitoxins. 


1.  See  Chapter  XI  (Part  II). 


366  INFECTION     AND     IMMUNITY. 

other.  There  is  no  third  substance  with  which  one 
or  the  other  may  unite.  In  the  body,  however,  the 
conditions  are  more  complex;  in  this  case  two  com- 
binations are  possible  for  the  toxin,  one  with  the 
antitoxin  which  has  been  introduced  and  a  second 
with  the  tissue  cells.  As  an  instance  of  the  great 
rapidity  with  which  toxin  may  unite  with  cells, 
the  work  of  Hej^mans  with  tetanus  toxin  may  be 
cited."  "Heymans  found  that,  if  all  the  blood  were 
removed  from  an  animal  a  few  minutes  after  the 
injection  of  a  single  fatal  dose  of  tetanus  toxin 
and  the  blood  of  another  animal  substituted,  still 
the  animal  died  of  tetanus^^  (Ritchie) ;  that  is  to 
say,  all  the  toxin  had  been  bound  by  the  cells  in 
that  brief  time. 
Biniiiiis-  of  Other  experiments  show  that  quantities  of  toxin 
Tissues,  and  antitoxin  which  are  neutral  when  mixed  be- 
fore injection  are  not  entirely  neutral  if  injected 
separately  and  at  different  points  of  the  body.  In 
this  instance  some  of  the  toxin  has  had  time  to 
unite  with  tissue  cells  before  it  could  come  in  con- 
tact with  the  antitoxin. 

Certain  work  by  Donitz  illustrates  not  only  the 
rapidity  with  which  toxin  may  be  bound  by  the 
tissue,  but  also  the  method  by  which  antitoxin  ef- 
fects a  cure.  In  relation  to  tetanus  he  found  that 
if  the  toxin  were  injected  first  and  the  antitoxin 
four  minutes  later,  a  quantity  of  antitoxin,  which 
was  slightly  in  excess  of  the  neutralizing  dose,  was 
required  to  prevent  the  development  of  tetanic 
symptoms;  if  he  waited  eight  minutes,  six  times 
as  much  antitoxin ;  after  sixteen  minutes,  twelve 
times  as  much ;  after  one  hour,  twenty-four  times 
the  simple  neutralizing  dose  was  required.  A  few 
hours  later  no  amount  of  antitoxin  could  save  the 


CURATIVE  ACTION'  OF  SElWMi^.  367 

animal.  Similar  conditions  were  met  in  the  neu- 
tralization of  diphtheria  toxin  by  its  antitoxin  in 
the  body.  Madsen,  in  performing  what  he  called 
"Curative  Experiments  in  the  iieagent  Glass/' 
found  that  the  longer  tetanolysin  had  been  in  con- 
tact with  erythrocytes,  the  more  antitetanolysin 
was  required  to  tear  away  the  toxin  from  the  cor- 
puscles. Practical  experience  with  diphtheria  also 
indicates  that  the  longer  the  disease  lasts  the  more 
antitoxin  is  required  for  cure. 

The  experiments  just  cited  give  us  a  clear  con- 
ception as  to  what  is  meant  by  the  curative  action 
of  an  antitoxin — an  action  which  consists  not  of 
the  neutralization  of  the  circulating  toxin,  but  of 
the  wresting  away  from  the  tissue  of  the  toxin 
which  has  been  bound.  Incidentally  the  circulat- 
ing toxin  is  neutralized,  and  for  this  step,  which 
is  essentially  prophylactic  in  nature,  the  simple 
equivalent  of  antitoxin  is  required.  But  for  the 
wresting  of  toxin  from  tissue  cells  not  a  mere 
equivalent  of  antitoxin,  but  a  great  excess,  is  re- 
quired, as  shown  by  the  experiments  of  Donitz  and 
of  Madsen. 

When  diphtheria  or  tetanus  has  advanced  so  far  )>*'»';«  <>' 
that  no  amount  of  antitoxin  will  effect  a  cure,  the  Action. 
relation  of  the  toxin  to  the  cells  has  become  some- 
thing more  than  mere  chemical  union.  Further 
processes  of  a  biologic  or  biochemic  nature  have  set 
in  in  which  the  toxin  may  have  become  an  integral 
part  of  the  protoplasm,  and  the  toxophorous  group 
may  have  begun  its  destructive  action,  whatever 
the  nature  of  this  action  may  be. 

It  is  important  to  recognize  that  antitoxin  can 
not  repair  an  injury  already  done  by  the  toxin. 
The  repair  of  the  injury  depends  on  the  recupera- 


368  INFECTION     AND     IMMUNITY. 

tive  power  of  the  cells;  hence,  antitoxin  cures  by 
tearing  from  the  cells,  perhaps  not  all,  but  so  much 
of  the  toxin  that  less  than  a  fatal  dose  remains  in 
the  cell. 

'^^ant^'pr?!!!  ^^^®  ^^^^  Icam  from  the  experiments  of  Donitz 
cipies.  and  of  Mad  sen  two  important  prirkciples  of  anti- 
toxic therapy :  First,  that  of  early  administration, 
i.  e.,  before  a  fatal  amount  of  toxin  has  been 
bound,  and,  second,  the  necessity  of  injecting  suffi- 
cient quantities  of  antitoxin. 

The  comparative  study  of  diphtheria  and  tet- 
anus has  clarified  the  principles  of  antitoxic 
therapy  to  no  small  degree.  Knowing  that  diph- 
theria antitoxin  has  a  much  greater  curative  value 
than  tetanus  antitoxin,  we  find  some  conditions 
which  would  seem  to  explain  the  difference,  at 
least  in  part. 
Tetanus.  In  regard  to  tetanus  we  have  the  following 
facts:  In  the  test-glass  the  affinity  between  the 
toxin  and  antitoxin  is  rather  weak,  since  approxi- 
mately forty  minutes  are  required  for  complete 
neutralization  (Ehrlich).  On  the  other  hand,  the 
experiments  of  Donitz  and  of  Heymans  show  that 
the  affinity  of  the  toxin  for  nervous  tissue  is  ex- 
ceedingly strong,  all  the  toxin  being  taken  up 
within  a  few  minutes.  These  two  conditions  alone 
suggest  the  probability  of  a  low  curative  value  on 
the  part  of  the  serum.  The  toxin  of  tetanus  also 
has  a  remarkable  selective  action  on  the  most  vital 
of  all  organs,  the  central  nervous  system ;  hence,  a 
/ower  grade  of  injury  may  prove  fatal  than  in 
other  infections  in  which  less  important  organs  or 
those  of  greater  recuperative  power  are  involved 
chiefly.  Furthermore,  it  seems  (Meyer  and  Kan- 
som,  Marie  and  Morax)  that  the  tetanus  toxin  is 


DIPHTHERIA.  369 

taken  up  by  the  nerve  endings  and  reaches  the 
ganglionic  cells  b}^  way  of  the  axis  cylinders, 
whereas  the  antitoxin  which  is  injected  remains 
chiefly  in  the  blood  and  lymphatic  circulations. 
Hence,  the  toxin,  to  a  certain  extent,  is  isolated 
and  less  accessible  to  the  action  of  the  antitoxin. 

Concerning  diphtheria,  the  affinity  between  Dipiitueria. 
toxin  and  antitoxin  is  relatively  strong,  for  com- 
plete neutralization  in  the  test-glass  takes  place  in 
about  fifteen  minutes  (Ehrlich).  On  the  other 
hand,  clinical  experience  indicates  that  the  affinity 
of  diphtheria  toxin  for  tissue  cells  is  less  than  that 
of  tetanus  toxin,  for  diphtheria  may  readily  be 
cured  on  the  second  or  third  day  of  the  disease,  * 

whereas  a  cure  of  tetanus  is  rarely  affected.  These 
would  seem  to  be  favorable  conditions  for  success- 
ful serum  therapy.  Although  the  toxin  of  diph- 
theria may  attack  the  nervous  system,  the  paraly- 
sis seen  in  such  cases  is  seldom  fatal.  On  the  basis 
of  anatomic  findings  in  fatal  cases  it  seems  prob- 
able that  the  greater  portion  of  the  toxin  is  taken 
up  by  parenchymatous  and  lymphatic  organs,  and 
by  connective  tissues  (animal  experiments),  which 
compared  with  the  nervous  tissue  are  of  less  imme- 
diate importance  for  life  and  have  greater  recuper- 
ative powers.  We  may  infer  from  clinical  experi- 
ence that  diphtheria  toxin  is  so  situated  in  the 
body  that  it  is  accessible  to  the  action  of  the  anti- 
toxin. 

We    have,     therefore,     the     following     factors    important 
which  apparently  are  of  importance  for  the  sue-  fo "  snJSels. 
cess  of  antitoxic  therapy:     1.  The  concentration 
(strength)  of  the  antitoxin  which  is  injected.    2. 
Its  freedom  from  contamination  and  adventitious 
toxins.    3.  The  time  of  its  administration.    4.  The 


370  INFECTION     AND     IMMUNITY. 

quantity  injected.     5.  The  degree  of  affinity  be- 
tween toxin  and  antitoxin.  6.  The  degree  of  affinity 
between  toxin  and  tissue  cells.    7.   The  amount  of 
toxin  which  may  be  bound  without  a  fatal  issue,  of 
which  the  vital  importance  of  the  organs  involved 
and  their  recuperative  powers  are  factors.     8.  The 
location  of  the  toxin  in  the  body,  i.  e.,  its  accessi- 
bility for  the  antitoxin. 
Prophylactic       What  has  bccu  said  relates  to  the  curative  ac- 
A?ituoxi?i.  tion  of  antitoxin.    It  is  evident  that  the  action  of 
antitoxin,  when  used  as  a  prophylactic,   is  of  a 
simpler  nature,  for  in  this  instance  the  conditions 
approximate   those   of   the   test-tube   experiment. 
'  There  has  been  opportunity  for  the  antitoxin  to 

become  uniformly  distributed  in  the  blood  and 
lymphatic  circulations;  hence,  it  is  able  to  meet 
and  to  bind  the  toxin  before  the  latter  comes  in 
contact  with  the  receptors  of  important  cells.  The 
high  value  of  tetanus  antitoxin  as  a  prophylactic, 
a  value  which  has  become  evident  in  recent  years, 
probably  depends  on  this  condition. 

The  immunity  which  is  afforded  by  a  prophy- 
lactic injection  of  antitoxin  is  of  short  duration, 
from  two  to  three  weeks;  the  antitoxin  is  excreted 
in  the  urine  to  a  considerable  extent,  but  in  part 
may  be  bound  and  assimilated  by  the  tissues. 

(b)    bactericidal  or  antibacterial  serums. 

Racierieidni  Attention  has  been  directed  repeatedly  to  a 
large  group  of  organisms  the  toxic  constituents  of 
which  are  integrally  associated  with  the  proto- 
plasm of  the  microbes;  the  toxic  substances  are 
endotoxins.  Certain  members  of  this  group,  of 
which  the  typhoid,  paratyphoid,  colon  and  dysen- 
tery bacilli  and  the  vibrio  of  cholera  are  represent- 


Serums. 


BACTERICIDAL  SERUMS.  371 

atives,  cause  the  development  of  strong  bacterici- 
dal serums  in  the  immunized  animal.  In  Chapter 
XVI,  A.  it  was  shown  that  such  serums  have  no 
power  of  neutralizing  the  endotoxins  of  the  corre- 
sponding organisms;  hence,  whatever  prophylactic 
and  curative  properties  they  may  have  would  seem 
to  depend  on  the  bactericidal  action  of  the  ambo- 
ceptor-complement  complex.  As  to  whether  the 
substances  which  stimulate  phagocytosis,  i.  e.,  the 
opsonic  or  bacteriotropic  substances  are  of  impor- 
tance for  the  intra  vitam  action  of  bactericidal 
serums,  remains  to  be  definitely  established. 

It  is  common  knowledge  that  bactericidal  curative 
serums  have  not  been  successful  curative  agents,  fac^tic  Po*wer. 
although  in  test-glass  experiments  they  may  be 
able  to  kill  large  numbers  of  organisms.  Experi- 
mental work  has  brought  to  light  a  number  of  con- 
ditions which  render  their  ineffectiveness  some- 
what intelligible,  but  this  knowledge  has  been  of 
little  service  in  increasing  their  value,  and  at  this 
moment  their  outlook  as  curative  agents  is  not  very 
encouraging. 

Animal  experiments  indicate  that,  prophylacti- 
cally,  they  are  much  more  powerful  than  when 
used  as  curative  agents.  Unfortunately,  however, 
as  in  the  case  of  antitoxins,  the  immunity  which  is 
conferred  is  of  short  duration,  the  serum  being  ex- 
creted or  the  antibodies  destroyed  within  two  or 
three  weeks.  For  this  reason  they  are  not  suited 
for  general  prophylactic  use  in  man,  but  they  may 
be  distinctly  useful  when  combined  with  vaccina- 
tion, as  indicated  later. 

Bactericidal  serums  are  efficient  in  saving  ex-  Tiine  of 
periment  animals,  provided  the  serum  is  injected 
in  advance  of,  simultaneouslv  with  or  verv  shortlv 


372  INFECTION     AND     IMMUNITY. 

after  the  bacteria  are  introduced.  By  injecting 
the  vibrio  of  cholera  and  anticholera  serum  simul- 
taneously one  may  readily  save  a  guinea-pig  from 
ten  times  the  fatal  dose,  or  more.  If  the  culture 
be  injected  first  and  the  serum  later  a  larger 
amount  of  serum  is  required  to  save  the  animal. 
After  a  few  hours  a  sufficient  amount  of  serum  to 
kill  all  the  vibrios  may  be  injected,  yet  the  ani- 
mal will  die  from  the  action  of  the  endotoxins 
which  have  been  liberated.  The  organisms  had 
proliferated  to  such  an  extent  that  the  mass, 
though  dead,  contained  a  fatal  amount  of  endo- 
toxin. A  statement  made  previously  may  be  re- 
peated, that  the  administration  of  a  bactericidal 
serum  rather  than  being  beneficial  may  actually  be 
injurious,  in  that  it  dissolves  the  micro-organisms 
rapid]}',  thereby  liberating  an  excessive  amount  of 
endotoxin,  this,  perhaps,  is  not  definitely  estab- 
lished as  a  point  of  practical  importance. 

Having  determined  the  amount  of  a  bactericidal 
serum  which  is  able  to  save  a  guinea-pig  from  an 
incipient  infection,  one  may  calculate  on  the  basis 
of  weight  the  amount  which  would  be  required  to 
save  a  man  under  the  same  conditions;  frequently 
it  amounts  to  impossible  quantities,  hundreds  of 
cubic  centimeters.  The  conditions  are  all  the  less 
promising  when  we  remember  that  phj^sicians  are 
usually  called  on  to  treat  well-established  rather 
than  incipient  infections. 
Pecniinritics  Other  couditious  which  operate  against  the  ef- 
meiit  ami  fectivcncss  of  bactcricidal  serums  as  curative 
niioeepoiM.  gggj^j-g  j^^yg  j.^  ^^  ^jj-|-^  peculiarities  of  comple- 
ments and  amboceptors.  The  lability  of  comple- 
ment involves  certain  difficulties.  A  bactericidal 
serum,  as  one  would  purchase  it,  contains  none, 


Atf  TIB  ACT  E  RIAL     SERUMS.  373 

because  of  its  spontaneous  degeneration.  Theo- 
retically, this  difficulty  may  be  obviated  in  three 
ways :  First,  one  may  use  serums  which  are  fresh 
from  the  immunized  animal ;  second,  one  may  com- 
plement the  solution  of  amboceptors  (old  immune 
serum)  by  the  addition  of  fresh  serum  from  a  nor- 
mal animal  which  is  known  to  contain  suitable 
complement;  or,  third,  one  may  inject  the  comple- 
ment-free serum  and  place  reliance  on  the  comple- 
ment wdiich  exists  in  the  plasma  and  lymph  of  the 
patient  for  activation  of  the  amboceptors.  It  is 
sufficiently  established  that  none  of  these  proce- 
dures enhances  the  curative  value  of  the  serums  to 
a  satisfactory  extent. 

Regardless   of  the   amount   of   foreign   comple-  Absorption 
ment  which  is  introduced,   it   appears  to  be   di-  meSt™?*^' 
verted  from  its  function.     It  has  been  shown  ex-  *'*^  Tissues. 
perimentally  that  the  tissues  may  absorb  a  foreign 
complement,  and  the  mere  fact  that  anticomple- 
ments  are  formed  so  readily  indicates  that  comple- 
ment may  be  bound  by  the  tissues.    In  accordance 
with   a   rather   general   principle,   if   the    animal 
which  furnishes  the  serum  is  remote  from  man 
zoologically  there  is  all  the  more  likelihood  of  the 
complement  being  fixed  by  human  tissues. 

It  has  been  suggested  that  if  one  should  choose  choice  of 
for  immunization  animals  which  are  closely  re-  foi-_  immuni- 
lated   to   man,   as   chimpanzees   and   monkeys,   a  ^ 
double  advantage  would  be  gained :    First,  the  for- 
eign complement  may  be  identical  or  similar  to 
that  in  man  and  consequently  would  be  less  likely 
to  be  absorbed  by  the  tissues;  and,  second,  the 
complementophilous  haptophores  of  the  ambocep- 
tors may  be  so  constructed  that  human  comple- 
ment would  serve  for  activation.     Theoretically, 


374  IXFECTION     AND     IMMUNITY. 

the  conditions  wonld  be  ideal  if  immune  human 
serum  were  available  for  therapeutic  purposes. 

If  one  depends  on  the  complement  in  the  pa- 
tient's body  for  activation  of  the  amboceptors, 
there  are  two  possible  difficulties  of  importance: 
First,  the  rfative  complement  of  the  body  is  often 
decreased  during  infections  and  in  some  chronic 
diseases  and  may  be  too  little  for  thorough  activa- 
tion; second,  the  amboceptors  of  the  immune 
serum  may  demand  for  their  activation  a  comple- 
ment or  complements  which  the  body  does  not  con- 
tain. 

Diversion  of  Divcrsiou  of  Complement  has  been  referred  to  as 
a  phenomenon  seen  m  test-tube  experiments,  in 
this  condition  an  excess  of  amboceptors  in  some 
way  decreases  the  power  of  the  serum;  by  an  ex- 
cess of  amboceptors  one  means,  in  this  instance, 
such  a  quantity  that  many  are  unbound  by  the 
bacteria.  It  is  supposed  that  a  certain  amount  of 
the  complement  is  absorbed  by  free  or  unbound 
amboceptors,  hence  the  effect  is  like  that  of  too 
little  complement.  In  the  desire  to  administer  a 
sufficient  amount  of  antibodies,  so  much  may  be 
introduced  that  diversion  of  the  complement  oc- 
curs in  the  body.  Eesults  obtained  by  Loffler  and 
Able,  by  Pfeiffer  and  by  Buxton  and  others,  in 
which  excessive  doses  of  immune  serum  were  less 
protective  than  moderate  doses,  show  that  a  simi- 
lar phenomenon  occurs  in  the  body. 

inacc-essiiiii-       jn  certain  diseases  the  microbes  are  so  situated 

ity    of    Mi- 
crobes, that  a  serum  as  ordinarily  administered  may  not 

be  able  to  reach  them.  Pfeiffer  thinks  that  there 
is  little  hope  for  the  serum  treatment  of  cholera 
because  of  the  exclusive  location  of  the  living  or- 
ganisms in  the  intestinal  tract.     In  typhoid  also 


ANTIBACTERIAL     SERUMS:  375 

the  intestines  are  a  reservoir  of  typhoid  bacilli, 
although  the  living  organisms  reach  the  circula- 
tion in  abundance. 

By  way  of  summary,  the  following  conditions 
appear  as  factors  in  the  low  curative  value  of  bac- 
tericidal serums:  1.  Bactericidal  serums  are  not 
antitoxic.  2.  They  may  liberate  an  excessive 
amount  of  endotoxin  by  dissolving  the  bacteria.  3. 
The  lability  of  exogenous  complement.  4.  The 
power  of  the  tissues  to  absorb  the  complements  of 
a  foreign  serum.  5.  The  lack  of  a  sufficient 
amount  of  suitable  complement  in  the  human 
body.  6.  The  difficulty  of  obtaining  amboceptors 
for  which  human  complements  are  suited.  7.  The 
possibility  of  diversion  of  complement  by  an  ex- 
cess of  amboceptors.  8.  Inaccessibility  of  the 
micro-organisms  in  certain  infections  (cholera, 
typhoid) . 

As' pointed  out  elsewhere,  another  group  of  or-  otiier  _«Aiiti 
ganisms,  the  members  of  which  contain  endo-  serums. 
toxins,  causes  the  formation  neither  of  antitoxins 
nor  of  bactericidal  serums;  streptococcus,  staphy- 
lococcus, pneumococcus,  etc.  Many  investigators, 
nevertheless,  are  positive  in  their  claims  that  the 
antiserums  for  these  organisms  have  a  protective 
and  even  a  curative  value.  The  properties  on  which 
their  value  depends  have  not  been  satisfactorily 
ascertained.  Although  certain  antistreptococcus 
serums  are  said  to  be  antitoxic,  it  is  contended  by 
others  that  they  act  by  stimulating  phagocytosis. 
It  has  been  shown  that  immunization  with  these 
organisms  causes  an  increase  in  the  opsonins. 
Their  curative  value  is  very  low  in  experimental 
Avork  and  they  fail  totally  if  injected  a  few  hours 


376  INFECTION     AND     IMMUNITY. 

subsequent  to  the  introduction  of  the  organisms. 
CJinically,  we  are  familiar  with  them  as  failures. 
It  is  particularly  in  relation  to  the  streptococ- 
cus that  the  so-called  polyvalent  serums  have  been 
prepared.  Cultures  of  streptococcus  obtained 
from  numerous  sources  are  used  in  the  immuniza- 
tion with  the  expectation  that  the  serum  will  be 
effective  against  various  strains  of  streptococci. 
The  principle  may  be  an  important  one  in  the 
preparation  of  other  antibacterial  and  bactericidal 
serums. 

(C)     VACCINATION. 

Vaccination  We  are  most  familiar  with  the  terms  vaccine 
**''iuocuiaUon^  and  vaccination  as  applied  to  protective  inocula- 
tion against  smallpox.  They  are  used,  however, 
with  equal  propriety  in  all  instances  in  which  the 
attenuated  or  killed  virus  of  a  disease  is  inoculated 
for  the  purpose  of  establishing  resistance  to  an 
infection.  The  process  set  in  motion  by  vaccina- 
tion is  one  of  active  immunization  in  which  the 
cells  are  induced  to  form  specific  antibodies  over  a 
long  period;  hence,  the  resistance  is  more  pro- 
tracted than  that  established  by  passive  immuni- 
zation. 

Certain  experimental  work,  as  previously  stated, 
indicates  that  the  acquired  resistance  persists  after 
the  formation  of  antibodies  has  ceased,  even  after 
the  quantity  of  the  latter  has  sunk  to  the  normal. 
This  condition  has  been  explained  by  assuming 
that,  as  a  consequence  of  vaccination,  the  cells  of 
the  body  have  been  "trained"  to  produce  the  cor- 
responding receptors;  hence,  when  the  micro-or- 
ganisms gain  entrance  at  a  subsequent  time  new 
antibodies  are  formed  so  rapidly  and  in  such  abun- 
dance that  the  incipient  infection  is  overcome. 


NEGATIVE    AND    POSITIVE    PHASES.       377 

In  some  instances  the  nature  of  the  virus  used 
is  unknown,  as  in  smallpox  and  hydrophobia:  in 
all  probability,  however,  it  consists  of  micro-or- 
ganisms rather  than  of  toxins  alone.  In  the  case 
of  typhoid,  cholera,  plague  and  other  diseases  of 
known  etiology  pure  cultures,  living  or  killed,  are 
inoculated.  Protection  does  not  follow  immedi- 
ately on  the  inoculation.  We  are  sufficiently  fa- 
miliar with  this  fact  in  relation  to  smallpox,  in 
which  several  days  are  required  for  the  formation 
of  a  protective  amount  of  the  antibodies.  There 
is  reason  to  believe  that  the  interval  between  the 
inoculation  and  the  appearance  of  antibodies  is 
characterized  by  a  decreased  resistance  on  the  part 
of  the  individual,  so  that  during  this  brief  period 
he  is  unusually  susceptible  to  infection. 

That  period  immediately  following  the  injec-  Negative  and 
tion  of  a  toxin  or  microbe,  in  which  the  quantity  Phases. 
of  antibodies  undergoes  a  temporary  decrease, 
Wright  speaks  of  as  the  negative  phase  of  the  im- 
munization; whereas  that  period  marked  by  the 
new  formation  of  antibodies  is  called  the  positive 
phase.  The  negative  phase  lasts  from  a  day  or 
two  to  several  days,  depending  on  the  quantity  and 
nature  of  the  virus  injected  (typhoid).  A  second 
injection  should  not  be  given  during  the  negative 
phase,  since  it  causes  a  further  decrease  in  the 
antibodies  and  prolongs  the  phase.  Wright  speaks 
of  this  as  a  cumulative  negative  phase.  A  cumu- 
lative positive  phase,  marked  by  the  formation  of 
larger  amounts  of  antibodies,  may  be  induced  by 
the  proper  spacing  of  a  number  of  injections. 

In  certain  instances  the   nature   of  the   anti-  Nature  of 
bodies  is  Imown.    In  typhoid,  cholera,  plague  and 
dysentery,  for  example,  they  consist  of  bactericidal 


378  INFECTION     AND     IMMUNITY. 

amboceptors;  agglutinins  and  precipitins  are 
formed  incidentall3^  The  amboceptors  naturally 
depend  on  the  complement  of  the  body  for  their 
activation.  If  the  disease  is  one  of  unknown  etiol- 
ogy the  nature  of  the  antibodies  is  not  easily  de- 
termined. We  should  keep  in  mind  the  possibil- 
ity that  vaccination  may  cause  an  increase  of  the 
opsonins  and  that  the  potential  phagoc^^tosis  may 
thereby  become  greater. 

In  case  the  incubation  period  of  the  vaccination 
is  shorter  than  that  of  the  disease  (smallpox,  hy- 
drophobia) vaccination  usually  is  successful  even  if 
practiced  within  a  limited  time  after  exposure  to 
infection. 

Vaccination  in  individual  diseases  is  considered 
in  Part  II. 

Theoretically  it  would  be  possible  to  immunize 

iiirmunfzaucm^  ^^^  agaiust  diphtheria  and  tetanus  by  inoculating 

with  small  amounts  of  the  corresponding  toxins. 

Such  a  procedure,  for  obvious  reasons,  would  be 

unnecessary  and  unjustifiable. 

It  is  not  unlikely  that  mixed  active  and  passive 
immunization  will  be  of  great  service  in  some  in- 
fections. A  successful  campaign  against  rinder- 
pest has  been  carried  on  in  the  Philippines  by  this 
method.  The  blood  of  infected  cattle  contains  the 
virus,  which  as  yet  has  not  been  cultivated  artifi- 
cially. The  serum  of  cattle  which  have  recovered 
from  the  disease,  or  which  have  been  immunized 
cautiously  with  infected  blood,  contains  the  speci- 
fic antibodies.  Both  the  immune  serum  and  viru- 
lent blood  are  used  for  the  inoculations.  The  same 
principle  has  been  found  effective  in  experimental 
work  with  cholera,  typhoid  and  plague.  Immedi- 
ate immunity  is  established  by  the  serum,  which 


Mixed    Active 


CURATIVE    TACCINATIOX.  379 

would  eliminate  the  danger  period  mentioned 
above,  and  before  the  serum  disappears  entirely 
active  immunity  develops. 

Wrioht,  followiniT  jiis  observations  on  the  varia-  ^""'*»**^'^. 
tions  in  opsonic  power  of  the  serum  in  different 
infections,  concluded  that  in  certain  localized 
chronic  infections  such  as  chronic  suppurative 
processes,  the  body  as  a  whole  did  not  respond  to 
the  infection  with  the  j^roduction  of  antibodies. 
The  injection  of  dead  homologous  organisms  was 
therefore  resorted  to  in  order,  in  the  words  of 
Wright :  ^^To  exploit  in  the  interests  of  the  in- 
fected tissues,  the  unexercized  immunizing  capac- 
ities of  the  uninfected  tissues." 

The  dosage  of  the  injected  vaccine  was  de- 
termined according  to  the  purpose  of  using  the 
minimum  quantity  which  would  result  in  the 
maximum  response  of  the  uninfected  tissues  with 
the  least  development  of  the  so-called  negative 
phase.  In  order  to  regulate  the  frequency  and 
size  of  the  therapeutic  inoculations,  Wright  made 
use  of  opsonic  index  estimations. 

Vaccines  are  prepared  as  follows : 

The  desired  organism  is  grown  on  a  suitable 
solid  medium  as  an  agar  slant  or  blood  serum 
slant  for  the  minimum  time  required  for  a  good 
growth,  usually  twenty-four  hours. 

Salt  solution  is  then  added  to  the  slant,  a  few 
cubic  centimeters  are  usually  sufficient  for  an 
ordinary  growth  (the  quantity  need  not  be  exact), 
and  the  culture  scraped  off  into  the  salt  solution 
with  a  sterile  glass  rod  or  platinum  loop.  The 
number  of  bacteria  per  cubic  centimeter  is  then 
estimated  by  mixing  equal  volumes  of  defibrinated 


380  IXFECTION     AND     IMMUNITY. 

blood  and  bacterial  suspension  and  then  diluting 
and  smearing  on  a  slide.  The  dilution  should  be 
about  five  times.  The  method  of  measuring  equal 
small  volumes  by  means  of  capillary  tubes  as 
given  in  Chapter  XIX,  may  be  used  and  a 
Romanowski  stain  used  for  staining. 

Since  the  number  of  corpuscles  in  normal 
human  blood  is  about  5,000,000,  by  a  comparison 
of  the  number  of  bacteria  with  the  number  of 
corpuscles  the  number  of  bacteria  per  cubic  cen- 
timeter can  be  readily  estimated.  By  dilution  with 
salt  solution  the  required  dosage  per  cubic  cen- 
timeter may  be  obtained.  When  it  is  necessary  to 
keep  the  vaccine  a  small  amount  of  tri-cresol  (.2 
per  cent.)  may  be  added. 

Recently  therapeutic  inoculations  have  been  used 
for  a  great  variety  of  infections,  both  acute  and 
chronic,  and  to  both  local  and  systemic  infections. 
Xaturally,  the  results  have  also  varied  within  wide 
range. 

In  case  of  chronic  localized  infections  the 
theoretical  basis  for  the  use  of  vaccines  seems 
plain.  As  pointed  out  by  Theobald  Smith :  "The 
effectiveness  of  vaccines  applied  in  the  course  of 
acute  febrile  diseases,  such  as  typhoid  fever  and 
pneumonia  must  be  accounted  for  by  principles  of 
which  experimental  medicine  has  as  yet  no  definite 
knowledge."  Theoretically  no  advantage  can  be 
expected  from  adding  toxins  in  an  already  over- 
intoxicated  case. 

This  criticism  does  not  apply,  of  course,  to  such 
a  procedure  as  is  suggested  by  Rosenow.  (See  chap- 
ter on  Pneumonia.) 


CHAPTER   XXIII. 


AXAPPIYLAXIS. 

Attention  has  already  been  called  to  the  fact 
that  an  individual  may  be  more  susceptible  to 
infections  at  one  time  than  at  another  through 
various  accidental  conditions,  as  exposure  and 
exhaustion.  This,  however,  is  not  a  specific  hyper- 
susceptibility  and  is  usually  more  or  less  transient. 

In  contrast  to  this  accidental  condition,  stands 
a  specific  susceptibility  which  is  now  commonly 
known  as  anaphylaxis.  The  condition  of  the  in- 
dividual or  animal  is  spoken  of  by  Y.  Pirquet  as 
allergy  (AUergie),  a  word  which  conveys  the  idea 
of  an  altered  power  of  reaction  on  the  part  of  the 
animal  body. 

V.  Pirquet's  conception  of  allergy  is  best  de- 
scribed in  his  own  words,  in  which  he  uses  vac- 
cination and  revaccination  as  an  illustration. 
"Vaccinia,  with  which  we  can  at  any  time  institute 
an  infection,  is  just  as  much  an  infectious  disease 
as  is  variola,  of  which  it  represents  an  attenuated 
form.  Let  us .  inoculate  one  person  who  was 
vaccinated  two  years  previously  and  who,  accord- 
ing to  the  customary  view,  is  immune,  with  a 
drop  of  lymph.  Then  inoculate  another  who  has 
not  gone  through  this  process  and  attend  it 
closely.  'Now  will  the  immune  person  show  ab- 
solutely nothing?  On  the  contrary,  when  we  re- 
turn after  24  hours,  we  find  in  the  one  who 
received  his  first  inoculation  (the  normal  person), 
a  small  crust  showing  no  reaction,  while  in  the 


382  INFECTION     AND    IMMUNITY. 

immune  there  is  a  normal  small,  raised,  inflam- 
matory, itching,  hyper emic  area. 

"Is  the  one  previously  inoculated,  therefore, 
hypersusceptible  ?  If  we  wait  a  few  days  the 
picture  changes :  The  papule  becomes  brownish 
and  smaller,  while  in  the  case  of  the  first  vaccina- 
tion, a  vesicle  forms  under  the  crust,  which  in- 
creases more  and  more,  becomes  surrounded  by  a 
wide  zone,  and  leads  to  a  pustule.  Now  we  must 
conclude  that  the  one  receiving  his  first  inocu- 
lation is  the  more  susceptible,  since  he  has  fever, 
pain,  and  a  marked  local  inflammation,  while  in 
the  immune  person  signs  of  infection  have  long 
since  disajDpeared. 

"As  it  appears  to  me  both  individuals  have 
reacted :  The  one  earlier,  the  other  later ;  one 
with  a  papule,  the  other  with  a  pustule.  In  one 
the  reaction  was  hardly  noticeable,  in  the  other 
pronounced.  Through  the  previous  inoculation 
no  immunity  in  the  sense  of  insusceptibility  has 
developed,  but  it  is  only  the  ability  to  react  which 
has  changed,  and  this  in  point  of  time,  quality, 
and  quantity.'' 

The  condition  then  appears  to  be  a  paradoxical 
one,  in  that  we  have  a  certain  degree  of  hyper- 
susceptibility  in  a  person  who  is  really  immune 
and  his  immunity  may  depend  to  a  greater  or 
less  degree  on  his  ability  to  react  quickly  to  the 
presence  of  the  infectious  agent  before  the  latter 
has  time  to  proliferate  extensively. 

Portier  and  Eichet,  in  1902,  observed  a  peculiar 
behavior  on  the  part  of  a  poison  found  in  certain 
actinia. 


A2JAPHYLAXIS.  383 

The  poison  was  invariably  fatal  for  dogs  when 
given  as  a  first  injection  in  doses  of  0.8  gm.  per 
kilogram  of  animal  weight,  but  was  rarely  fatal 
in  doses  of  under  0.2  gm.  per  kilogram.  Death 
usually  occurred  in  from  four  to  nine  days.  When 
a  second  dose,  however,  was  given  to  an  animal 
which  had  recovered  from  the  first  injection, 
death  supervened  in  a  short  time,  usually  within 
two  and  three-quarters  hours.  The  first  injection 
evidently  modified  the  resistance  of  the  animal  in 
some  way  so  that  it  became  more  susceptible  to 
the  poison  than  it  was  in  the  first  instance.  It 
was  to  this  modified  state  of  the  animal's  resist- 
ance that  Eichet  applied  the  name  '^^anaph3daxis," 
which  stands  in  contrast  to  a  condition  of  pro- 
phylaxis. 

In  1903,  Arthus  observed  that,  when  rabbits  Artims'  Phe- 
had  received  several  injections  of  horse  serum  at 
intervals  of  several  days,  the  serum  ceased  to  be 
absorbed  as  at  first  and  that  there  resulted  local 
necrosis  and  often  sloughing  with  subsequent  ulcer 
formation. 

In  1904,  Theobald  Smith  told  Ehrlich  of  a  Tiieobaid 
phenomenon  which  he  had  observed  while  testing  phenomenon. 
the  potency  of  diphtheria  antitoxin  on  guinea- 
pigs.  Animals  which  had  received  injections  of 
antitoxic  horse  serum  and  later  were  injected  with 
a  small  quantity  of  normal  horse  serum  became 
acutely  ill  or  died. 

In  the  following  year,  1905,  appeared  the  ar- 
ticles of  Otto,  Eosenau  and  Anderson,  and  of  v. 
Pirquet  and  Schick.  Since  these  articles  an 
enormous  amount  of  work  has  been  done  to  cor- 


384  INFECTION     AND     IMMUNITY. 

relate  the  phenomena  of  anaphylaxis  with  other 
processes  of  immunity. 

Like  other  processes  of  immunity  anaphylaxis 
may  be  classified  as  natural  and  acquired;  and, 
again,  acquired  anaphylaxis  may  be  active,  in 
which  the  process  results  from  a  reaction  on  the 
part  of  the  tissue  cells,  or  may  be  passive — result- 
ing from  the  introduction  of  ready-made  sub- 
stances into  the  body. 
Natural"  It  has  bccu  loug  kuowu  that,  as  noted  by 
Horwitz,  Schofield,  Doerr,  and  others,  certain  in- 
dividuals are  unusually  affected  by  the  ingestion 
of  eggs,  crabs,  flesh,  pork,  etc.  The  symptoms 
are  variable,  but  there  is  often  nausea,  fever,  colic, 
and  exanthemata.  It  is  of  course  to  be  questioned 
as  to  whether  such  hypersusceptibility  is  really 
natural  or  acquired  by  early  sensitization.  Scho- 
field reports  such  a  case  of  hypersusceptibility  to 
egg  which  disappeared  after  repeated  increasing 
doses  of  egg  taken  in  pills,  using  minute  amounts 
to  begin  with.  Such  hypersusceptibility  has  been 
long  known  under  the  name  idiosyncracy.  The 
idiosyncracies  to  proteins,  however,  should  be  dis- 
tinguished from  those  in  which  known  chemical 
substances,  such  as  mercury  or  salicylic  acid,  are 
concerned. 

Active  anaphylaxis  has  been  studied  in  a  variety 
of  mammals  and  fowls,  and  substances  which 
correspond  to  those  concerned  in  immunization 
have  been  demonstrated. 

It  will  be  well  to  take  up  these  various  factors, 
and  after  a  discussion  of  their  nature,  it  will  be 
easier  to  understand  the  theories  concerning  the 
mechanism  of  their  action. 


ANAPHYLAXIS.  385 

The   sensitizing   agent   in   anaphylaxis  has   re-  Antigren. 

ceived  the  name  of  anaphylactogen,  or  sensibili- 
sinogen,  and  may  be  defined  as  any  substance 
which,  when  taken  into  the  body,  produces  a 
specific  hypersusceptibility,  usually  after  an  incu- 
bation period  of  at  least  from  five  to  seven  days. 

The  substances  which  have  been  demonstrated 
to  act  as  anaphylactogens  are  proteins  or  are  in- 
separably connected  with  proteins.  That  anaphy- 
lactogens are  closely  related,  or,  as  Friedberger, 
Doerr,  and  others  think,  identical  with  those 
bodies  which  produce  complement  deviation,  anti- 
bodies, and  precipitins,  is  shown  by  the  fact  that 
the  same  substances  produce  all  three  phenomena. 
Thus,  as  with  precipitinogens  we  have  an  anaphy- 
laxis specific  for  species  and  for  tissues.  The 
same  tissues  which  are  specific  for  precipitin  for- 
mation, cr3'talline  lens,  spermatozoa,  and  placenta, 
also  give  a  specific  anaphylaxis,  while  those  tissues 
such  as  kidney,  liver,  etc.,  which  produce  only 
species  specific  precipitins  produce  species  specific 
anaphylaxis.  As  an  exception  to  this  rule,  it  may 
be  mentioned  that  Wells  does  not  find  that  iodized 
albumin  produces  anaphylaxis  specific  for  iodized 
albumins  rather  than  species  specific  reactions,  as 
was  found  for  precipitins  by  Obermayer  and  Pick. 

One  of  the  first  questions  which  arose  concern-  Relation  tr 
ing  Theobald  Smith's  phenomenon  was  that  of  the  Toxicity. 
relation  of  the  anaphylactogen  to  the  diphtheria 
toxin  and  antitoxin.  In  this  case,  the  employment 
of  normal  horse  serum  readily  showed  that  an- 
aphylaxis was  independent  of  the  diphtheria  bacil- 
lus derivatives  and  antitoxin  present  in  the  serum. 


SenBltlzatlon 
and     Toxicity. 


386  INFECTION     AND     IMMUNITY. 

Somewhat  more  difficult  is  the  question  regard- 
ing the  primary  toxicity  of  such  substances  as  are 
contained  in  eel  serum,  various  phytalbumins  and 
bacteria.  It  has  been  shown  by  Doerr  and  Eau- 
bitschek  that  by  heating  or  by  acidifying  eel  serum 
it  is  possible  to  remove  the  primary  toxicity  with- 
out taking  away  the  property  of  producing  anaphy- 
laxis. In  a  similar  way  it  has  been  shown  by 
Eosenau  and  Anderson,  Vaughan,  and  others,  that 
bacterial  proteins  free  from  toxic  Action  can  pro- 
duce anaphylaxis.  It  has  also  been  shown  that 
whereas  in  primarily  toxic  serum  the  larger  the 
dose  the  greater  the  toxicity,  in  anaphylaxis  sensi- 
tization smaller  doses  sensitize  more  readily  than 
large  ones. 

That  hypersusceptibility  to  true  toxins  does  oc- 
cur, however,  has  been  demonstrated  in  the  case  of 
diphtheria  toxin  and  tetanus  toxin.  The  phe- 
nomena here,  however,  are  distinct  from  anaphy- 
laxis in  the  fact  that  the  incubation  period  is 
absent,  that  the  S3miptoms  come  on  gradually  after 
the  second  dose,  and  lastly,  that  after  a  certain 
length  of  time  which  corresponds  to  the  incuba- 
tion time  of  anaphylaxis,  immunity  or  decrease  in 
susceptibility,  occurs  in  contrast  to  anaphylaxis. 
We  must  conclude,  then,  that  toxicity  and  sensi- 
tizing properties  are  distinct  from  each  other. 

The  anaphylactogen  comes  into  consideration  in 
the  primary  or  sensitizing  dose  and  in  the  second- 
ary or  toxic  dose.  Many  experiments  have  been 
carried  out  to  determine  whether  or  not  the  sen- 
sitizing and  toxic  action  are  dependent  on  the 
same  substance  or  similar  qualities  of  the  same 
substance.    It  was  found,  for  instance,  that  in  the 


SENSITIZATION  AND  TOXICITY.  387 

case  of  egg  albumin  one  twenty  millionth  of  a 
^ram  sufficed  for  sensitization  (Wells),  and  about 
one  thousand  times  that  amount  was  required  for 
a  toxic  dose.  It  was  also  found  that  by  heating 
to  90°  or  100°  C.  it  became  much  more  difficult 
to  cause  intoxication  in  sensitized  animals  than 
to  sensitize  them.  Besredka  concluded  from  these 
experiments  that  sensitizing  and  toxic  substances 
were  distinct  from  each  other.  Yaughan  and 
Wheeler  by  digestion  with  hot  absolute  alcohol  and 
sodium  hydrate  obtained  a  separation  of  albumin 
into  two  parts,  one  of  which  showed  a  marked 
sensitizing  property  and  l3ut  little  toxicity  (alcohol 
insoluble  portion)  ;  the  other  portion  (alcohol 
soluble),  a  more  highly  toxic  action.  They  con- 
cluded that  toxic  and  sensitizinaj  substances  were 
present  in  the  same  molecule  and  that  by  their 
process  a  splitting  of  the  molecule  into  toxic  and 
sensitizing  groups  was  obtained. 

The  work  of  Vaughan  and  Wheeler  was  done 
on  whole  egg  white  and  other  crude  proteins. 

Wells,  working  with  pure  crystallized  albumin, 
obtained  toxic  and  sensitizing  action  in  this  way 
in  quantities  smaller  than  those  represented  by 
Yaughan's  minimum  sensitizing  and  toxic  split 
products.  It  seems  possible,  therefore,  that  by  the 
process  of  Yaughan  and  Wheeler  amounts  of  pro- 
tein too  small  to  produce  toxic  effects,  but  capable 
of  sensitizing,  escaped  splitting  through  alcohol 
precipitation  while  the  alcohol  soluble  portion  con- 
sisted of  toxic  split  products.  The  action  of  heat 
ma}^  be  due  to  the  fact  that  both  toxic  and  sensi- 
tizing substances  are  equally  influenced,  but  that 
the  apparent  effect  is  greater  on  toxicity  because 


388  INFECTION     AND     IMMUNITY. 

for  intoxication  larger  amounts  are  necessary  than 
for  sensitization. 

Wells  has  also  shown  that  toxicity  and  sensi- 
tizing properties  decrease  equally  by  tryptic  diges- 
tioUj  and  that  both  disappear  with  the  disappear- 
ance of  heat  coagulable  proteins.  According  to 
Wells,  the  importance  of  the  action  of  heat  is  due 
to  the  coagulation  of  protein,  thus  rendering  it 
capable  of  being  taken  up  and  digested  by  the 
leucocytes.  Casein  and  other  proteins  which  do 
not  coagulate  on  boiling  suffer  no  change  through 
heat  until  a  temperature  which  destroys  the  pro- 
tein molecule  is  reached. 

That  toxic  and  sensitizing  substances  may  be 
closely  related  to  the  aromatic  groups  of  the  pro- 
tein molecule  is  suggested  by  the  fact  that  gelatin 
which  is  devoid  of  tyrosin  and  contains  little  of 
other  aromatic  groups  does  not  produce  the  phe- 
nomena of  anaphylaxis  (Wells). 
Anaphylactic  By  the  injection  of  serum  of  sensitized  animals 
'  it  is  possible  to  produce  a  passive  sensitization, 
analogous  to  passive  immunity,  and  in  this  way 
to  demonstrate  the  presence  of  an  anaphylactic 
antibody.  This  antibody  has  received  the  name  of 
"anaphylactin"  (Eosenau  and  Anderson),  or  ''^al- 
lergin'^  (Anderson  and  Frost).  It  is  possible  to 
produce  passive  anaphylaxis  in  various  animals, 
but,  as  in  active  anaphylaxis,  the  guinea-pig  is 
best  adapted  to  the  purpose.  Transmission  of 
anaphylaxis  from  one  species  to  another  is  also 
possible.  From  rabbit  to  guinea-pig  anaphylaxis 
is  readily  transmitted. " 

The  necessary  interval  of  time  elapsing  between 
the  injection  of  the  scrum  containing  anaphylactic 


ANAPHYLACTIC  ANTIBODY.  -389 

antibody  and  the  actual  sensitization  of  the  animal 
varies  with  the  different  methods  of  injection.  In 
case  of  intraperitoneal  injection  this  time  is  about 
twenty-four  honrs;  in  intravenous  injections  it  is 
about  one  and  one-half  hours. 

Different  means  of  measuring  the  sensitizing 
strength  of  antiserums  have  been  suggested.  Doerr 
and  Euss  injected  decreasing  quantities  of  the 
serum  into  guinea-pigs  and  then  by  injecting 
twenty-four  hours  Jater  an  intoxicating  quantity 
of  antigen  into  each  of  these  pigs^  the  amount  of 
antiserum  necessary  to  produce  sensitization  was 
found.  A  second  method  is  to  inject  a  definite 
quantity  of  antiserum  into  each  of  a  series  of  pigs 
and  then  twenty-four  hours  later  to  inject  decreas- 
ing quantities  of  antigen  to  find  the  smallest 
amount  necessary  to  cause  acute  death.  Doerr 
and  Euss  suggest  as  a  unit  of  anaph3daxis  anti- 
serum or  of  anaphylactin  such  a  serum  as  will  in 
a  dose  of  1  c.c.  intraperitoneally  sensitize  a  250 
gm.  guinea-pig  so  that  acute  death  may  be  pro- 
duced in  twenty-four  hours  by  injecting  a  sufficient 
quantity  of  antigen. 

The  close  connection  between  anaphylactogen  Relation  to 
and  precipitinogen  has  already  been  alluded  to.  Antiiiodies. 
In  a  similar  way,  anaphylactin  and  precipitin  are 
so  closely  allied  that  Friedberger,  Doerr,  and 
others  consider  them  identical.  As  objections  to 
this  view  it  is  pointed  out  that  animals  which  do 
not  readily  produce  precipitins,  such  as  guinea- 
pigs  and  dogs,  are  most  susceptible  to  sensitization ; 
and  secondl}',  that  in  the  state  of  antianaphylaxis, 
to  be  described  later,  precipitins  may  be  present, 
but  apparently  the  anaphylactin  is  exhausted. 


390  INFECTION     AND     IMMUNITY. 

The  anaphylactic  antibody  is   thermostabile   as 

are  precipitins  and  agglutinins.    That  is,  it  resists 

a  temperature  of  56°  C.  for  one-half  hour. 

Tbe  Role  of       Michaelis  and  Fleischmann  observed  that  dur- 

in  Ana-  iug  and  after  anaphylactic  shock  the  serum  of  the 

pbyiaxis.   ^jjjj-^^r^|   became   poor   in   complement.      Sleeswijk 

found  that  following  the  second  antigen  injection, 

complement  began  to  disappear  after  five  minutes, 

and  this  disappearance  became  marked  in  thirty 

minutes.      In    cases    in    which    death    took    place 

quickly   and   complement   disappearance   was   not 

yet  far  advanced  a  further  disappearance  could  be 

found  by  allowing  the  serum  to  stand  for  a  while 

in  the  test  tube. 

That  the  disappearance  of  complement  is  in 
itself  not  responsible  for  the  anaphylactic  shock 
is  shown  in  two  ways :  first,  the  injection  of  com- 
plement before  or  after  the  second  antigen  injec- 
tion does  not  prevent  shock,  and  secondly  in  most 
rapidly  fatal  shock,  death  takes  place  before  com- 
plement has  disappeared  to  any  extent.  Friedber- 
ger  and  Hartoch  have  also  shown  that  injection  of 
complement-binding  salt  solution  inhibits  ana- 
phylactic symptoms,  when  it  is  injected  before  the 
second  injection  of  antigen  (see  Chapter  on  Com- 
plement Deviation). 
Anapiiyio-  In  Order  to  study  further  the  relation  of  com- 
plement to  anaphylaxis,  Friedemann  sensitized 
rabbits  to  ox-blood  corpuscles  and  then  added 
inactivated  serum  from  these  rabbits  to  ox  erythro- 
cytes in  the  test-tube.  He  found  that  when  com- 
plement vras  added  to  such  a  mixture,  it  became 
toxic  and  capable  of  producing  anaphylactic  symp- 
toms.    By    preventing    complement    binding,    by 


toxin. 


Considera- 
tions. 


THEORIES     OF     A'NAPEYLAXIH.  391 

complementoid,  etc.,  the  formation  of  toxin  was 
prevented.  Friedberger  was  able  in  a  similar  way 
to  produce  substances  which  caused  symptoms  of 
anaphylaxis,  by  treating  precipitinogens  from 
various  sources  with  precipitins  in  the  presence 
of  complement.  He  therefore  supposes  that  this 
toxic  substance,  which  he  calls  anaphylatoxin,  is 
derived  from  the  precipitate  caused  by  precipitin 
acting  on  precipitinogen,  and  that  it  is  the  specific 
cause  of  intoxication  in  anaph3daxis.  As  there 
exists  a  difference  of  opinion  as  to  the  identity  of 
anaphylactin,  so  there  exist  various  theories  as  to 
the  formation  of  anaphylatoxin. 

Eichet  supposed  that  anaphylactic  antibody  and  Theoretical 
antigen  combined  to  form  the  poisonous  substance 
which  he  called  "apotoxin.^^  AYolff-Eisner,  Weich- 
hardt,  Friedemann  and  others  consider  anaphyl- 
actin to  be  of  the  nature  of  a  lytic  amboceptor, 
and  that,  j^y  the  action  of  complement  through 
this  amboceptor,  a  splitting  of  anaphylactogen 
into  toxic  substances  takes  place.  Yaughan  and 
Wheeler,  with  others,  consider  that  in  sensitiza- 
tion we  have  to  do  with  the  development  of  spe- 
cific proteolytic  ferments  which  split  the  antigen 
into  toxic  groups  similar  in  nature  to  their  toxic 
products  obtained  by  hydrolysis  with  alcohol  and 
sodium  hydrate.  This  view  is  supported  by  the 
fact  that  Biedl  and  Kraus  have  produced  symp- 
toms of  anaphylaxis  by  injection  of  split  products 
of  protein  (Witte's  peptone)  in  dogs.  The  pro- 
duction of  increased  protein  splitting  power  of  the 
serum  after  injection  of  foreign  proteins  as 
demonstrated  by  Abderhalden  also  supports  the 
enzyme  theory.     According  to  these  views,  various 


392  INFECTION     AND     IMMUNITY. 

anaphyla  toxins  are  of  similar  character  but 
formed  through  the  action  of  substances  which 
are  of  specific  nature. 
Symptoms  of  The  sjmptoms  of  anaphylaxis  vary  with  differ- 
ent animals.  It  is  in  the  guinea-pig  that  most 
constant  results  are  obtained.  Symptoms  begin 
at  different  intervals  of  time,  after  the  second 
injection,  with  different  proteins.  With  animal 
proteins,  they  appear  in  about  fifteen  minutes 
after  intraperitoneal  injection.  Tlie  symptoms 
usually  appear  somewhat  later  with  vegetable  pro- 
teins. The  animal  becomes  restless,  there  is  a 
tendency  to  scratch,  the  hair  stands  on  end,  and 
difficulty  in  breathing  comes  on.  Paralysis  of  the 
hind  legs  is  common  with  animal  proteins  but  is 
less  common  in  plant  proteins.  The  respiration 
becomes  spasmodic,  the  animal  is  unable  to  stand, 
convulsive  movements  occur,  and  death  follows 
rapidly  when  a  fatal  dose  is  given.  When  a  non- 
lethal  dose  is  given  symptoms  may  be  delayed  for 
an  hour.  Death  commonly  occurs  in  fatal  cases 
inside  of  an  hour  and  often  in  less  than  half  an 
hour.  In  intravenous  and  intracardiac  injections, 
the  symptoms  follow  much  more  rapidly  than  in 
intraperitoneal  injections.  In  subcutaneous  injec- 
tions, the  symptoms  occur  long  after  injection  and 
are  inconstant  and  much  less  severe  than  with 
other  ways  of  absorption.  Fatal  results  are  much 
more  difficult  to  produce  in  subcutaneous  injec- 
tions. 

The  blood  pressure  is  raised  and  lowering  does 
not  take  place  until  shortly  before  death.  A  very 
important  symptom  is  that  described  by  Pfeiffer, 
who  observed  a  constant  sudden  drop  in  tempera- 


MECHANISM    OF   SHOCK.  393 

ture.  This  symptom  is  considered  of  great  diag- 
nostic value  when  the  drop  amounts  to  2°  or  3°  C. 
and  other  experimental  conditions  are  constant. 

In  dogs^  the  symptoms  vary  greatly  from  those 
in  guinea-pigs.  Here  a  characteristic  fall  in  blood 
pressure  is  found.  Vomiting,  involuntary  urina- 
tion and  defecation,  paralysis  and  narcosis  are 
common  symptoms. 

The  respiratory  mechanism  of  shock  in  guinea- 
pigs,  according  to  Auer  and  Lewis,  is  that  of  a 
spasmodic  contraction  of  the  unstriped  muscle  of 
the  bronchioles  resulting  in  obstruction  of  the 
lumen,  acute  emphysema  and  death  from  asphyxi- 
ation. 

Section  of  the  vagi  does  not  influence  this  pul- 
monary phenomena,  indicating  that  the  effect  is 
a  peripheral  one.  Schultz  has  shown  that  the 
unstriped  muscle  fiber  of  a  sensitized  guinea-pig 
contracts  more  vigorously  when  specific  serum  is 
applied  directly  to  it  than  when  other  serum  is 
used.  Atropin,  which-  acts  on  the  nerve  endings, 
causes  an  inhibition  of  symptoms.  Marked  con- 
gestion of  the  abdominal  blood  vessels  is  a  com- 
mon finding  at  autopsy.  Various  hypnotic  and 
narcotic  drugs  have  been  described  as  inhibiting 
anaphylactic  symptoms,  but  the  effect  seems 
mainly  due  to  a  masking  of  symptoms. 

A  sensitized  animal  which  has  recovered  from  a  Antianapityi- 
non-lethal  toxic  dose  of  protein  is  refractory  to 
the  action  of  a  later  dose.  The  condition  of  such 
an  animal  is  known  as  antianaphylaxis,  and  it 
has  been  demonstrated  by  failure  to  produce  pas- 
sive anaphylaxis  by  using  the  serum  of  an  animal 
in  a  state  of  antianaphylaxis,  that  the  condition 


394  INFEGTIOy     A^'D     IMMUNITY. 

is  due  to  an  exhaustion  of  anaphylactic  antibody. 
In  animals  which  have  been  actively  sensitized, 
the  period  is  a  transient  one,  followed  by  a  return 
of  hypersusceptibility  due  to  continued  production 
of  antibodies.  In  passively  sensitized  animals,  as 
there  is  no  further  source  of  antibodies,  the  result 
depends  on  the  amount  of  antigen  injected.  If, 
for  instance,  the  animal  is  insufficientlv  sensitive 
to  allow  of  death  from  a  large  toxic  dose,  the  anti- 
gen remaining  will  produce  an  active  sensitization. 
If  the  antigen  is  just  enough  to  neutralize  the 
anaphylactin,  the  animal  will  then  be,  as  before, 
sensitized.  If  the  second  dose  is  too  small  to 
neutralize  the  anaphylactin,  that  which  remains 
will  be  capable  of  producing  further  reactions.  In 
animals  immunized  to  proteins  and  which  have  a 
high  concentration  of  antibodies  in  the  blood,  so 
that  passive  anaphylaxis  may  be  transmitted  to  a 
second  animal  by  the  use  of  a  small  quantity  of 
serum  of  the  immune  animal,  a  state  of  antiana- 
phylaxis  may  be  produced  by  injections  of  amounts 
of  antigen  too  small  to  produce  a  fatal  result. 
In  this  case,  we  have  an  animal  which  is  antiana- 
phylactic  although  possessing  a  serum  containing 
a  high  concentration  of  anaphylactin.  Friedberger 
supposes  that  in  this  case  the  receptors  of  the  cells 
are  occupied  by  anaphylactic  antibody  which  is 
not  reached  by  the  injected  antigen,  this  being 
neutralized  by  the  circulating  anaphylactin. 
Tabercniin  The  relation  of  the  tuberculin  reaction  to  ana- 
ceptibiiity.  phylaxis  (scc  Tubcrculosis)  has  been  the  subject 
of  much  discussion.  ^ 

Yamanouchi   succeeded    in   producing  anaphyl- 
actic symptoms  in  guinea-pigs  by  sensitizing  thera 


tiERUM    DISEASE.  395 

with  serum  from  tuberculous  patients  and  then, 
twent3'-four  hours  later,  injecting  tuberculin  or 
tubercle  bacillus  emulsion.  Bail  passively  sensi- 
tized guinea-pigs  b}'  the  injection  of  tuberculous 
tissues  and  in  this  way  obtained  anaphylactic 
symptoms  by  injecting  tuberculin  after  twenty- 
four  hours.  Helmholtz  produced  passive  sensiti- 
zation against  cutaneous  reaction  by  the  injection 
of  serum  from  tuberculous  guinea-pigs  into  nor- 
mal guinea-pigs  so  that  after  twenty-four  hours, 
they  gave  a  positive  v.  Pirquet  test. 

In  contrast  to  the  results  of  Yamanouchi  and 
Bail,  other  investigators  have  succeeded  in  passive 
sensitization  of  guinea-pigs  by  injection  of  serum 
from  tuberculous  animals  either  only  occ,asionally 
or  not  at  all.  Production  of  anaph3'laxis  by  active 
sensitization  with  tuberculin  is  possible  only  after 
repeated  large  doses.  It  would  seem,  therefore, 
that  as  in  the  case  of  other  bacteria,  typhoid,  dys- 
enterv,  etc.,  the  anaphylaxis  is  against  the  proteins 
of  the  tubercle  bacillus  rather  than  the  toxin  pro- 
duced by  it. 

The  untoward  symptoms  following  the  injec- 
tion of  curative  serums  has  been  the  subject  of 
study  by  many  investigators,  particularly  v.  Pir- 
quet and  Schick,  Eosenau  and  Anderson,  and 
AVeaver. 

The  reaction  following  a  primary  injection  of 
serum  appears  after  a  period  of  time  varying  from 
a  few  minutes  to  several  weeks.  There  may  be 
slight  redness  and  itching  at  the  inoculation  site, 
and  swelling  of  the  adjacent  lymph  glands.  The 
prominent  symptoms  are  fever,  skin  eruptions, 
edema  and  joint  pains.  Slight  albuminuria  and 
leukopenia  have  been  noted. 


Serum   Dis- 
ease. 


396  INFECTION     AND     IMMUNITY. 

The  reaction  varies  in  severity  with  the  amount 
of  serum  used  but  individual  variation  and  differ- 
ences in  the  serum  are  the  most  important  factors. 
The  reaction  following  a  second  injection  v.  Pir- 
quet  and  Schick  divide  into  (a)  immediate, 
appearing  after  a  few  hours,  or  (b)  delayed, 
appearing  after  a  few  days  or  a  week.  The  S3^mp- 
toms  are  similar  to  those  following  a  primary 
injection  but  are  more  likely  to  be  severe  and  may 
be  accompanied  by  vomiting,  convulsions,  collapse 
and,  rarety,  death. 

The  abnormal  reactions  following  a  second 
injection'  are  more  likely  to  appear  when  the 
patient  has  had  a  reaction  after  the  primary  injec- 
tion; secondly,  when  large  amounts  of  serum  have 
been  given  in  the  primary  injection;  and  thirdly, 
with  a  history  of  asthma  (especially  in  asthma  in 
which  the  attacks  are  brought  on  by  proximity  to 
horses)  or  hay  fever. 

It  has  been  suggested  that,  in  cases  necessitating 
second  injections  of  antitoxin,  a  small  amount, 
1  c.c.  or  less,  be  given  as  a  test  dose  to  be  followed 
by  the  necessary  therapeutic  dose  twenty-four 
hours  later. 

It  is  important  to  be  sure  that  the  antitoxin  is 
not  injected  into  the  vein  because  of  the  fact  that 
anaphylactic  symptoms  are  produced  as  much 
more  readily  by  intravenous  injections.  This  can 
be  avoided  by  preliminary  aspiration  just  before 
injection  to  see  that  blood  does  not  enter  the 
syringe. 

Rosenau  and  Anderson  have  demonstrated  the 
presence  of  anaphylactin  in  the  blood  of  men  who 
have  been  injected  with  antitoxic  horse  serum. 


SERUM    DISEASE.  397 

It  has  been  suggested  that  by  passive  sensitiza- 
tion of  guinea-pigs  with  patient's  serum,  we  can 
ascertain  whether  or  not  there  is  any  danger  in 
second  injections  of  serum. 

It  has  also  been  suggested  that  a  cutaneous  test, 
similar  to  a  v.  Pirquet  tuberculin  test,  be  made- 
with  horse  serum  to  find  out  whether  or  not  hyper- 
susceptibility  to  horse  serum  be  present. 


PART   THREE-SPECIAL. 


CHAPTER    XXIV. 


Although  a  consistent  classification  of  the  infec- 
tious diseases,  on  the  basis  of  immunity,  is  impos- 
sible at  the  present  time,  a  certain  grouping  is  de- 
sirable for  the  sake  of  convenience.  The  following 
arrangement  of  those  diseases  we  are  able  to  con- 
sider is  made  on  a  basis  which  is  partly  etiologic, 
partly  with  reference  to  the  pathogenic  properties 
of  the  micro-organisms,  and  partly  to  the  nature 
of  the  reactions  excited  in  the  body  by  infection  or 
immunization.  In  some  instances  nothing  more 
than  general  analogies  suggest  themselves  as  a 
basis  for  the  grouping,  which  is  necessarily  provi- 
sional and  imperfect. 

GROUP  J. 

Diseases,  natural  or  experimental,  which  are 
caused  by  soluble  toxins  of  bacterial,  animal  or 
plant  origin.  Infection  or  immunization  induces 
immunity  to  subsequent  attacks  (except  in  hay  fe- 
ver), the  immunity  being  characterized  by  the 
formation  of  serum  antitoxins,  and  occasionally  of 
bacteriolysins  and  agglutinins.  The  serums  of 
highly  immunized  animals  are  protective  and  cur- 
ative for  the  corresponding  intoxications  in  man 
and  other  animals. 

A.    BACTERIAL  DISEASES. 
I.    DIPHTHERIA. 

Bacillus  diplithericc,  or  the  Klebs-Loefflcr  bacil- 
lus, was  discovered  by  Klebs  in  1883,  and  more 


DIPHTHERIA    BACILLUS. 


399 


Cliaracter- 
istics  of  the 
Organism. 


fully  described  by  Loeffler  in  1884.  It  answers  all 
Koch's  laws  in  its  relationship  to  the  disease  of 
diphtheria.  It  is  a  non-motile,  rod-shaped  organ- 
ism having  about  the  length  of  the  tubercle  bacil- 
lus, but  twice  its  thickness.  One  end  commonly 
presents  a  flask-like  enlargement.  It  stains  by 
Gram's  method,  with  the  ordinary  anilin  dyes,  ana 
with  the  special  stain  of  Neisser  shows  a  peculiar 
granulation,  the  granules  of  Babes-Ernst.  It  is 
readily  cultivated,  especially  on  solid  media  which 
contain  serum  and  in  various  bouillons.  It  tends 
to  grow  in  coherent  masses  and  under  the  micro- 
scope the  cells  often  show  a  characteristic  phalanx- 
like arrangement. 

The  diphtheria  bacillus  is  an  obligate  parasite 
having  no  vegetative  existence  outside  of  the  body, 
is  very  resistant  to  desiccation  and  may  remain 
virulent  in  a  dried  state  for  from  one  to  five 
months.  Its  life  in  water  varies  from  a  few  days 
to  several  weeks,  having  its  shortest  existence  in 
distilled  water  and  its  longest  in  hydrant  water 
which  has  been  boiled.  It  disappears  more  quickly 
from  unboiled  hydrant  water.  It  is  very  suscepti- 
ble to  ordinary  antiseptics,  being  killed  in  a  few 
minutes  by  corrosive  sublimate  even  in  a  dilution 
of  1  to  10,000. 

The  sources  of  infection  may  be  enumerated  as  3ietiiods  of 
follows:  1.  From  the  false  membranes,  sputum 
or  excretions  of  the  mouth,  pharynx,  nose,  con- 
junctiva and  deeper  respiratory  passages  of  in- 
fected individuals.  2.  From  convalescents  and 
those  who  have  fully  recovered,  even  after  serum 
treatment.  Virulent  organisms  may  persist  in  the 
pharynx  or  nose  of  convalescents  for  weeks  and 
months,  as  in  one  of  Prip's  cases  in  which  they 


400  INFECTION     AND     IMMUNITY. 

were  found  twenty- two  months  after  recovery.  3. 
From  the  npper  air  passages  of  healthy  persons 
who  .may  never  have  had  diphtheria^  but  who  have 
been  in  direct  or  indirect  contact  with  the  dis- 
eased. Kober  obtained  virulent  bacilli  from  8  per 
cent,  of  the  individuals  who  had  been  in  direct 
contact  with  patients,  and  he  states  that  0.83  per 
cent,  of  the  people  at  large  carry  with  them  viru- 
lent organisms.  This  condition  may  well  account 
for  the  ^^spontaneous"  origin  of  diphtheria  in  the 
susceptible.  4.  From  cases  of  latent  diphtheria  as 
represented  by  chronic  pharyngeal  diphtheria  and 
chronic  rhinitis  fihrinosa. 

Hence,  infection  takes  place  chiefly  by  direct 
contact,  but  frequently  also  by  indirect  contact. 
Transmission  by  kissing  or  by  other  means  of  inti- 
mate contact,  by  using  infected  cups  or  toys,  is 
well  recognized.  "Droj^let  infection,"^  i.  e.,  from 
infected  globules  of  mucus  or  saliva  which  the  pa- 
tient emits  when  speaking  or  coughing,  may  occur, 
but  perhaps  is  not  of  great  significance.  The  same 
probably  is  true  of  "dust  infection,"  although,  as 
stated,  the  organism  may  remain  living  and  viru- 
lent in  a  dried  state  for  a  long  time.  The  disease 
is  rarely  transmitted  from  animals  to  man,  al- 
though such  transmission  may  occur  from  the  cat, 
which  occasionally  suffers  from  true  diphtheria. 
The  diphtheria  of  fowls  is  due  to  another  organ- 
ism. 

The  upper  air  passages,  more  rarely  the  conjunc- 
tiva, wounds  and  the  vulva,  are  recognized  as  in- 
fection atria. 
Pathogrenesis.  The  local  and  general  phenomena  of  diphtheria 
are  caused  by  the  soluble  toxin  which  the  organ- 
ism secretes.     Although  the  toxin  is  not  absorbed 


DIPHTHERIA    BACILLUS. 


401 


through,  nor  does  it  injure  the  Tinbroken  skin,  it 
produces  necrosis  of  the  mucous  surfaces  and  un- 
derlying tissue  at  the  site  of  infection.  Through 
the  wounded  surface  fibrin-forming  elements  es- 
cape^ as  a  consequence  of  which  successive  layers 
of  fibrin  are  deposited  and  the  fibrin,  together  with 
the  necrotic  surface,  leucocytes  and  associated 
micro-organisms  constitute  the  membrane  which 
so  often  marks  the  disease  clinically.  The  local 
process  is  similar  in  diphtheria  of  cutaneous 
wounds.  The  toxin  becomes  generalized  by  absorp- 
tion through  the  lymphatic  circulation. 

Characteristically  the  bacilli  are  confined  to  the 
site  of  infection.  Although  diphtheritic  bacterie- 
mia  rarely  occurs,  the  bacilli  have  been  found  oc- 
casionally in  the  blood  and  viscera  of  fatal  cases. 

The  clinical  and  anatomic  conditions  lead  us  to 
believe  that  the  parenchymatous  organs,  the  lym- 
phatic tissues  and  the  cells  of  the  nervous  system 
contain  receptors  with  w^hich  the  toxin  unites,  in- 
asmuch as  these  tissues  su.ffer  demonstrable  injury 
during  the  disease.  When  the  toxin  is  injected 
subcutaneously  into  animals,  localized  edema  and 
necrosis  occur;  hence,  the  connective  tissues  may 
also  take  up  a  portion  of  the  toxin,  diverting  it,  so 
to  say,  from  the  more  vital  organs. 

Mixed  infections  render  diphtheria  a  more  dan- 
gerous disease.  According  to  Baumgarten,  the 
streptococcus  is  associated  with  the  diphtheria  ba- 
cillus in  most  cases  of  diphtheria.  The  observa- 
tion of  Eoux  and  Yersin  that  the  streptococcus  in- 
creases the  virulence  of  the  diphtheria  bacillus 
both  in  the  test-tube  and  in  animal  experiments 
may  explain  to  some  degree  the  severity  of  the  dis- 
ease when  accompanied  by  streptococcus  infection. 


Localization 
of  tlie  Bacilli. 


3iixed 
Infections. 


402  INFECTION     AND     IMMUNITY. 

Aside  from  the  local  influence  of  the  streptococcus, 
however,  a  general  invasion  by  this  organism  may 
occur,  with  such  consequences  as  acute  nephritis 
or  lobular  pneumonia,  and  in  this  condition  the 
diphtheritic  infection  may  fall  into  the  back- 
ground in  importance  (septic  diphtheria).  Post- 
diphtheritic suppurations  commonly  are  caused  by 
the  pyogenic  cocci,  but  sometimes  in  association 
with  the  diphtheria  bacillus  itself.  Earely  the 
bacillus  is  found  in  pure  culture  in  lobular  pneu- 
monia, a  condition  which  Flexner  and  Anderson 
produced  experimentally  in  animals.  In  puer- 
peral infections  with  the  streptococcus  a  puerperal 
diphtheria  is  sometimes  superimposed. 
Immunity  and  Very  young  children  resist  diphtheritic  infec- 
snsceptibiiity.  ^^^^^^  ^Y  certain  degree  of  immunity  may  be  trans- 
mitted by  the  mother.  Observations  on  animals 
show  that  when  the  blood  and  milk  of  the  mother 
contain  antitoxin,  the  offspring  acquires  some  pro- 
tection, which,  however,  may  disappear  after  the 
cessation  of  nursing.  Polano  claims  that  anti- 
toxin passes  from  the  mother  to  the  child  through 
the  placenta.  From  the  second  to  the  seventh  or 
eighth  5'ear  children  usually  are  very  susceptible. 
This  susceptibility  is  not  uniform,  however,  for 
many  children  escape  infection,  whereas  others, 
under  the  same  conditions,  contract  the  disease. 
Following  this  period  susceptibility  decreases  and 
after  the  fifteenth  year  the  disease  is  relatively 
rare. 

The  cause  of  the  immunity  which  develops  in 
the  absence  of  a  preceding  infection  has  not  been 
sufficiently  investigated.  In  some  cases  consid- 
erable amounts  of  antitoxin  are  found  in  the 
serum,  perhaps  enough  to  account  for  the  immun- 


IMMUNITY     IN     DIPHTHERIA.  403 

ity.  The  prolonged  presence  of  bacilli  of  low 
virulence  in  the  nose  or  pharjoix,  or  mild  attacks 
of  the  disease  which  have  not  been  recognized, 
may  cause  the  development  of  antitoxin.  As 
stated  in  an  earlier  chapter,  the  loss  of  suitable 
receptors  may  be  a  factor  in  this  type  of  acquired 
immunity. 

Hypertrophic  tonsils  and  chronic  pharyngitis 
appear  to  be  predisposing  causes  in  children. 

Spontaneous  recovery  (active  immunity)  is  due 
to  the  formation  of  the  specific  antitoxin  by 
the  tissues  of  the  patient.  We  may  regard  the 
relationship  of  the  leucocytes  to  diphtheritic  in- 
fection as  not  definitely  settled.  Although  leuco- 
cytosis  is  a  fairly  constant  occurrence  and  may  go 
as  high  as  25,000  to  30,000  to  the  cubic  milli- 
meter, it  is  difficult  to  dissociate  that  due  to  the 
diphtheritic  infection  from  that  caused  by  a  mixed 
infection  with  the  streptococcus.  Both  polynu- 
clears  and  mononuclears  are  increased,  the  latter 
being  especially  marked  in  children  (Ewing). 
The  opsonin  content  of  the  serum  in  diphtheria  is 
below  normal  at  the  onset  of  the  disease.  As  the 
symptoms  subside  and  the  membrane  disappears, 
the  opsonic  index  rises  considerably,  returning  to 
normal  in  from  two  to  nine  days. 

Injection  of  dead  diphtheria  bacilli  in  suitable 
numbers  into  rabbits  is  followed  by  a  rise  in  the 
opsonic  index.  Injection  of  dead  diphtheria  bacilli 
may  prove  of  service  in  ridding  the  throats  of 
bacillus-carriers   of  bacilli    (Tunnicliff). 

Eecent  experiments  have  substantiated  the  ideas 
of  Behring  that  bacteriolysins  are  of  little  impor- 
tance in  immunity  in  diphtheria. 


Active   Im- 
munity. 


404  INFECTION     AND     IMMUNITY. 

The  duration  of  active  immunit}^  to  diphtheria 
varies  greatly.  Usually  an  individual  has  diph- 
theria but  once,  yet  not  infrequently  those  are  en- 
countered who  suffer  from  repeated  attacks.  In 
some  instances  the  susceptibility  continues  into 
adult  life. 

Fropbyiaxis.  The  advcut  of  Serotherapy  justifies  no  relaxa- 
tion in  the  customary  prophylactic  measures,  such 
as  isolation  of  the  diseased,  quarantine  and  disin- 
fection. A  patient  should  not  be  considered  harm- 
less until  his  mouth,  pharynx  and  nose  are  free 
from  bacilli,  a  condition  which  may  be  brought 
about  by  antiseptic  applications,  and  for  the  de- 
termination of  which  repeated  bacteriologic  exam- 
inations are  necessary.  "The  danger  that  others 
who  have  been  in  contact  with  the  patient  may 
carry  the  infection  should  be  met  by  appropriate 
treatment.  It  is  not  to  be  forgotten  that  anti- 
toxin does  not  destroy  the  organisms.  The  injec- 
tion of  antitoxin  is  our  most  effective  measure  for 
individual  prophylaxis. 

serotiierapy.  Experimentally,  it  is  possible  to  vaccinate 
against  diphtheria  by  the  inoculation  of  dead  diph- 
theria bacilli,  or  extracts  of  agar  cultures  (Lip- 
stein,  also  Bandi  and  Gagnoni),  but  the  conditions 
hardly  warrant  the  use  of  this  method  for  pro- 
tecting man.  Extracts  of  the  organisms  may  be 
mixed  with  antitoxin  and  injected  for  protection. 
This  is  the  so-called  serovaccination. 

The  efficacy  of  diphtheria  antitoxin  is  so  well 
known  that  little  comment  is  needed.  It  has 
caused  a  reduction  of  more  than  50  per  cent,  in 
the  mortality  of  the  disease;  from  41  per  cent,  to 
8  or  9  per  cent.,  according  to  Baginsky. 


DIPHTHERIA    ANTITOXIN.  405 

For  prophylaxis  from  500  to  1,000  units  are 
generally  recommended,  although  some  foreign 
authorities  give  only  250  units.  Rarely,  individ- 
uals who  have  received  such  treatment  develop 
diphtheria  within  twenty-four  hours  after  the  in- 
jection. In  these  cases  it  is  probable  that  infec- 
tion has  already  occurred  and  symptoms  appear 
before  the  antitoxin  is  thorougjily  distributed. 
Naturally  one  may  contract  diphtheria  after  the 
antitoxin  is  eliminated. 

For  curative  purposes  the  amount  actually  re- 
quired depends  on  the  virulence  of  the  infection 
and  the  duration  of  the  disease.  Inasmuch  as  the 
virulence  may  not  be  Imown  accurately,  what  ap- 
pears to  be  an  excess  of  antitoxin  is  always  de- 
manded. Having  in  mind  the  average  dose  of 
3,000  units  recommended  by  the  recent  edition  of 
the  United  States  Pharmacopeia,  the  physician 
must  be  guided  by  the  conditions  in  the  individ- 
ual case.  Less  than  2,000  units  are  rarely  indi- 
cated, and  as  many  as  10,000  and  14,000  units 
may  be  given  without  detriment  to  the  patient. 
There  should  be  no  hesitation  about  repeating  a 
dose  within  twenty-four  hours  in  the  absence  of 
distinct  improvement. 

Eansom  and  Knorr  state  that  if  the  antitoxin 
is  given  intravenously,  which  may  be  done  without 
danger,  the  action  of  the  serum  is  about  eight 
hours  earlier  than  when  given  subcutaneously.  In 
severe  and  in  late  cases  it  is  advisable  to  use  this 
method  of  introduction,  the  serum  first  being 
warmed  to  the  temperature  of  the  body.  It  should 
be  remembered,  however,  that  the  dangers  of  ana- 
phylactic symptoms  are  much  increased  by  intra- 
venous injection. 


Paralysis. 


406  INFECTION     AND     IMMUNITY. 

It  is  probable  that  few  cases  are  so  mild  or  so 
hopeless,  unless  moribund,  that  the  omission  of 
antitoxin  is  justifiable. 
Diphtheritic  The  belief  that  antitoxin  favors  the  development 
of  diphtheritic  paralysis  is  no  longer  held.  If 
there  has  been  an  actual  increase  in  the  percentage 
of  cases  which  suffer  from  paralysis/ as  sometimes 
stated,  it  is  because  a  larger  number  of  severe 
cases  is  saved;  and  the  severe  cases  are  those 
in  which  the  patients  most  frequently  develop 
paralysis.  If  we  accept  the  view  of  Ehrlich  that 
a  special  toxin  of  weak  affinity  for  the  anti- 
toxin, i.  e.,  the  toxon,  causes  the  paralysis,  we  find 
all  the  more  Justification  for  large  doses  of 
antitoxin,  for  antitoxin  neutralizes  the  toxon  as 
well  as  the  toxin.  On  the  basis  of  experi- 
mental work  Eansom  concludes:  "Transferring 
the  results  (of  experiments)  to  practice  among 
human  beings,  we  may  expect  liberal  doses  of 
antitoxin  given  early  in  the  illness  to  influence 
favorably  the  subsequent  paralysis;  and  this  fa- 
vorable influence  is  likely  to  manifest  itself,  not  so 
much  in  the  local  paralyses  (soft  palate,  etc.),  as 
in  such  fatal  symptoms  as  failure  of  the  heart. 
Severe  cases,  however,  are  likely  to  be  followed  by 
some  paralysis  in  spite  of  even  large  doses  of  anti- 
toxin." 

Cases  in  which  there  is  severe  mixed  infection, 
septic  diphtheria,  respond  less  favorably  to  anti- 
toxic therapy  than  uncomplicated  cases.  At  some 
time  a  mixed  serum  therapy  suited  to  the  mixed 
infection  may  be  possible. 

The  suggestion  made  by  Wasserman  of  a  com- 
bined treatment  with  bactericidal  and  antitoxic 
serums  has  not  been  applied  practically. 


P8EUD0DIPHTHERIA    BACILLUS.  407 

Inasmuch  as  the  serum  of  the  patient  does  not  Agglutination 

.  .  Test 

■develop  agglutinins,  the  agglutination  test  is  of 
no  value  for  the  recognition  of  the  disease.  If  ani- 
mals are  immunized  with  the  bacillus,  agglutinins 
are  said  to  be  formed.  The  serum  of  such  an  ani- 
mal may  be  used  for  the  identification  of  a  culture 
made  from  the  throat,  but  this  would  have  no 
practical  value,  for  the  diagnosis  may  be  estab- 
lished by  the  ordinary  bacteriologic  methods  much 
more  quickly  and  satisfactorily.  It  is  difficult  to 
obtain  a  homogeneous  suspension  of  the  bacillus 
for  the  agglutination  test. 

Microscopically  and  culturally  the  bacillus  of  Pseudodipii- 
diphtheria  can  be  distinguished  with  difficulty  Bacnii. 
from  a  variety  of  other  organisms  which  belong  to 
the  same  group,  and  which  are  called  pseudodiph- 
theria  bacilli.  The  latter  are  frequently  found  in 
diphtheritic  throats,  but  occur  also  in  the  upper 
air  passages  and  conjunctiva  in  the  absence  of  all 
lesions.  On  the  whole,  they  are  non-pathogenic, 
but  occasionally  a  culture  is  found  which  causes  a 
subcutaneous  infiltration  at  the  point  of  injection 
in  an  experimental  animal.  Hamilton  cultivated 
one  which  was  distinctly  virulent  for  animals.  Their 
paijiogenicit}^,  however,  is  altogether  different 
from  that  of  the  diphtheria  bacillus  inasmuch  as 
diphtheria  antitoxin  does  not  protect  against  them 
nor  do  animals  which  are  immunized  with  pseudo- 
diphtheria  bacilli  become  immune  to  the  toxin  of 
diphtheria.  The  Bacillus  xerosis,  which  is  thought 
by  some  to  be  the  cause  of  xerosis  conjunctivae, 
but  which  is  also  found  under  normal  conditions, 
is  a  pseudodiphtheria  bacillus.  The  animal  experi- 
ment is  the  only  positive  means  of  differentiating 
the  true  from  the  pseudodiphtheria  bacilli.     Some 


408  INFECTION     AND     IMMUNITY. 

consider  them  as  diphtlieria  bacilli  which  have  lost 
their  virulence. 

The  presence  of  these  organisms  may  complicate 
the  diagnosis  of  diphtheria  in  some  cases,  but 
there  is  little  danger  of  serious  error.  If  one 
found  organisms  resembling  the  bacillus  of  diph- 
theria in  a  membranous  sore  throat  which  was  ac- 
companied by  severe  symptoms^  there  could  be  no 
wavering  in  the  decision  to  use  antitoxin. 

II.   TETANUS. 

In  1884   Carle  and  Eattone  demonstrated  the 

infectiousness  of  tetanus  by  inoculating  the  pus 

from  an  infected  wound  into  rabbits;  11  of  the  12 

inoculated  rabbits  died  of  tetanus.     In  1885  the 

bacillus  was  discovered  by  Nicolaier,  and  Kitasato 

cultivated  it  artificially  in  1889. 

Character-       The  Organism  is  rather  long  and  slender  (2  to 

'Jiic^oorgan-  4  microus  long,  0.3  to  0.5  broad),  possesses  many 

fsm.   fiagella  and  has  a  small  amount  of  motility.     It 

stains  readily  with  the  ordinary  anilin  dyes  and  by 

Gram's  method.     In  young  cultures  isolated  cells 

and  threads   predominate,   but  after   a  few  days 

spore  formation  begins;  eventually  all  the  adult 

cells  degenerate  and  the  culture  consists  entirely 

of  spores.    The  spores  have  a  larger  diameter  than 

the  bacillus,  are  situated  at  one  end  of  the  cell  and 

give    the    latter    the    characteristic    "drumsticlc^' 

•  form.     The  organism  is  a  strict  anaerobe  and  is 

obtained    in    pure    culture    with    some    difficulty. 

Morphologically  it  is  difficult  to  distinguish  from 

the  bacilli  of  malignant  edema  and  symptomatic 

anthrax. 

Habitat.       Few  orgauisms  are  distributed  more  widely  and 

generously  than  the  bacillus  of  tetanus.  It  is  most 


TETANUS   BACILLUS.  409 

abundant  in  street  dirt  and  in  tilled  ground  which 
has  been  fertilized  with  manure.  Nicolaier  found 
it  in  twelve  out  of  eighteen  samples  of  earth.  It 
is  less  abundant  in  timber  land.  Such  a  distribu- 
tion is  easily  accounted  for,  since  the  bacillus 
seems  normally  to  be  an  inhabitant  of  the  intesti- 
nal tract  of  the  horse,  cow  and  sheep,  and  is  often 
found  in  that  of  man  and  other  animals.  It  oc- 
curs on  dirty  clothing  and  readily  gains  access  to 
dwellings  with  dust  in  which  it  may  be  blown  and 
carried  about.  Tetanus  frequently  develops  in 
gunshot  wounds  in  which  dirty  clothing  is  carried 
into  the  tissue,  and  several  instances  of  house 
tetanus  have  been  noted  in  which  a  number  of  in- 
dividuals in  the  same  dwelling  have  contracted  the 
disease  following  injury.  Particular  localities  may 
be  heavily  infected.  In  certain  tropical  districts  a 
large  percentage  of  new-born  infants  die  of  tetanus 
neonatorum,  and  puerperal  tetanus  has  prevailed 
alarmin^'h^  in  Bombav.  It  has  been  su^o-ested 
that  the  custom  of  l3leaching  the  linen  on  the 
ground  may  be  responsible  for  the  prevalence  of 
the  disease  in  these  localities,  but  from  the  fact 
that  it  has  decreased  under  aseptic  practices  the 
general  lack  of  surgical  precautions  is  probably  of 
greater  importance.  Tetanus  has  resulted  from 
the  injection  of  impure  gelatin  for  hemostatic 
purposes.  The  bacillus  has  been  found  in  sea 
water. 

The  ability  of  the  bacillus  to  proliferate  outside 
the  animal  body  has  not  been  determined.  Some 
observers  hold  that  it  exists  as  a  vegetative  organ- 
ism only  in  the  intestinal  tract  of  animals,  but  the 
possibility  of  proliferation  in  soil  is  by  no  means 
excluded,  particularly  since  it  is  so  often  found  in 


410  INFECTION     AND     IMMUNITY. 

association  with  organisms  which  are  known  to 
favor  its  growth.  When  incrusted  in  solid  ma- 
terial and  accompanied  by  suitable  saprophytes  it 
may  readily  find  the  anaerobic  conditions  which 
are  demanded  for  germination  of  the  spores. 
Resistance.  The  sporcs  are  very  resistant.  In  one  instance 
they  remained  virulent  for  eleven  years  on  a  splin- 
ter of  wood.  They  may  be  killed  in  six  days  by 
direct  sunlight.  In  comparison  with  non-spore- 
forming  organisms  they  are  very  resistant  to  anti- 
septics. Kitasato  found  that  they  were  killed  in 
five  minutes  by  steam,  in  fifteen  hours  by  a  5  per 
cent,  carbolic  acid,  in  two  hours  by  5  per  cent, 
carbolic  acid  to  which  0.5  per  cent,  of  hydro- 
chloric acid  was  added,  in  three  hours  by  1  to  1000 
corrosive  sublimate  and  in  thirty  minutes  by  the 
same  solution  to  which  0.5  per  cent,  hydrochloric 
acid  had  been  added. 
Infection       Tctanus  is  couspicuously  a  wound  infection  and 

dition^"wSi?h  that  it  develops  so  frequently  from  wounds  which 
infecfion*!  ^^^  Contaminated  with  earth  is  readily  understood 
from  the  distribution  of  the  organisms  as  cited 
above.  Considering,  however,  the  great  number  of 
such  wounds  and  the  prevalence  of  the  bacillus, 
the  rarity  of  the  disease  is  remarkable.  In  expla- 
nation of  this  fact  investigations  have  shown  that 
the  organism  is  not  a  vigorous  parasite,  that  it 
demands  special  conditions  for  its  development  in 
the  tissues.  According  to  Vaillard  and  Rouget, 
the  spores  when  washed  free  of  toxin  do  not  cause 
tetanus,  but  rather  are  taken  up  and  destroyed  by 
leucoc3des. 
Anaerobic       The  bacillus,  furthermore,  is  a  strict  anaerobe, 

condiHons^^in  (jgj^^nding   for   its    development   a   wound   from 
which  the  air  is  largely  excluded.     It  is  well  loiown 


CONDITIONS   OF   INFECTION.  411 

that  penetrating  wounds  in  which  infected  ma- 
terial is  carried  beneath  the  fasciae,  as  the  rusty 
nail  wounds,  also  those  accompanied  by  deep  lac- 
erations, as  wounds  inflicted  with  blank  cartridges, 
or  those  in  which  dirt  and  micro-organisms  have 
been  ground  into  the  tissues,  as  in  crushing  inju- 
ries, are  prone  to  be  followed  by  tetanus.  Under 
•such  conditions  the  bacillus  lies  deeply  imbedded 
in  the  tissues  and  remote  from  the  air. 

Of  equal  importance  is  the  presence  of  foreign  inhibition  of 

,  ,  n  X-       1      1         J!      j_i  •  •  PJiagocytosis. 

matter  and  particularly  oi  other  micro-organisms. 
Eelatively  superficial  wounds  in  which  there  is 
laceration  of  the  tissue  with  consequent  necrosis, 
as  in  wounds  by  toy  pistols,  even  the  paper-cap 
pistol,  are  well  adapted  foT  the  development  of 
tetanus  if  the  germs  were  on  the  sldn  at  the  time 
of  injury.  Necrotic  tissue  favors  the  proliferation 
of  the  tetanus  bacilli  in  two  ways.  In  the  first 
place  it  seals  up  the  wound  to  a  certain  extent, 
and  thus  provides  the  requisite  anaerobic  condi- 
tion; in  the  second  place  it  would  seem  to  prevent 
phagocytosis  of  the  bacilli  in  some  obscure  way. 
It  has  been  suggested  that  the  strong,  chemotactic 
relation  which  exists  between  necrotic  material 
and  leucocytes  causes  the  latter  to  take  up  the  dead 
tissue  rather  than  the  bacilli.  That  innocent  for- 
eign material  may  favor  the  development  of  teta- 
nus in  the  presence  of  the  microbes  was  shown  by 
Vaillard  and  Eouget:  tetanus  would  develop  in 
the  presence  of  an  artificially  produced  hematoma 
or  a  subcutaneous  fracture  while  in  the  absence  of 
such  predisposing  factors  the  bacilli  were  taken  up 
by  phagocytes. 

Saprophytic   organisms   and  the  pus-producing  J^^i^e^^ 
cocci  Avhich  are  usually  found  in  wounds  contami- 


412  INFECTION     AND     IMMUNITY. 

nated  with  earth  appear  to  favor  the  development 
of  tetanus.  This  may  be  explained  to  some  extent 
by  their  ability  to  increase  the  virulence  of  the 
tetanus  bacillus,  a  condition  which  is  noted  in  cul- 
tures. In  the  wound  they  may  engage  the  leuco- 
cytes in  phagocytosis  and  prevent  ingestion  of  the 
tetanus  bacilli.  As  aerobic  organisms  they  may 
facilitate  development  of  the  bacilli  by  consuming 
local  oxygen. 

Our  great  harvest  of  tetanus  following  Fourth- 
of-July  injuries  is  closely  associated  in  the  first 
place  with  the  warm,  dry  season  in  which  the 
bacilli  are  more  readily  disseminated  with  dust, 
and  in  the  second  place  with  the  nature  of  the 
wound  and  mixed  infections,  as  described  above. 

Occasionally  tetanus  follows  the  simplest 
wounds,  which  may  have  healed  entirely  before 
symptoms  develop.  In  "idiopathic  tetanus"  and 
in  the  so-called  "tetanus  rheumaticus,"  which  fol- 
lows exposure  to  cold,  the  infection  atria  are  un- 
known. In  the  latter  instance  a  latent  infection, 
whicn  is  stirred  into  activity  by  the  reduction  of 
resistance  which  often  follows  exposure,  may  be 
present;  a  virulent  tetanus  bacilli  (?)  were  culti- 
vated from  the  lungs  of  one  such  patient.  The  oc- 
casional occurrence  of  tetanus  following  diphthe- 
ria and  typhoid  suggests  that  infection  may  take 
place  through  wounds  of  mucous  surfaces.  Neither 
the  bacillus  nor  its  toxins  penetrate  the  unbroken 
skin  or  mucous  membranes,  and  the  alimentary 
tract  is  further  protected  by  the  ability  of  the  gas- 
tric and  pancreatic  juices  to  digest  the  toxin. 
Period  of  The  incubation  period  varies  from  two  or  three 
i.cnbation.  ^^^^  ^^  scvcral  wccks.  In  the  statistics  of  Eose  20 
per  cent,  of  tlie  cases  showed  symptoms  in  the  first 


ACTION    OF    TETANUS    TOXIN.  413 

week^  45  per  cent,  in  the  second^  and  about  30  per 
cent,  in  the  third  or  fourth  weeks.  The  shorter 
the  incubation  period  the  more  fatal  the  disease. 
In  the  statistics  cited  the  mortality  with  short  in- 
cubation was  91  per  cent. ;  when  the  incubation 
period  was  moderate  it  was  81.3  per  cent.,  and 
when  prolonged,  52.9  per  cent.  The  nearer  the 
infection  atrium  is  to  the  central  nervous  sj^stem 
the  shorter  is  the  incubation  period;  ^^ead  teta- 
nus^^  develops  quickly. 

The  pathogenic  properties  of  the  tetanus  bacil- 
lus reside  in  its  soluble  toxins,  of  which  two,  teta- 
nospasmin  and  tetanolysin,  are  known.  The  char- 
acteristic nervous  phenomena  of  the  infection  de- 
pend on  the  action  of  the  former,  whereas  the  lat- 
ter, a  hemolytic  toxin,  is  of  minor  importance.  As 
in  diphtheria,  a  systemic  distribution  of  the  bacilli 
is  not  necessary  for  the  development  of  the  dis- 
ease, the  toxin  being  produced  by  the  organisms  in 
the  wound,  whence  it  is  carried  to  the  nervous 
tissue  by  way  of  the  lymphatics.  Particularly  in 
mixed  infections  tetanus  bacilli  may  be  carried  to 
neighboring  lymphatic  glands  and  eventually 
reach  the  circulation;  pure  cultures  have  been  ob- 
tained from  the  hearths  blood  in  experimental 
work.  The  blood,  on  account  of  its  content  in 
oxygen,  is  thought  to  be  unfavorable  for  the 
growth  of  the  organism. 

Just  before  death  the  toxin  has  been  demon- 
strated in  the  blood  of  man  by  injecting  some  of 
the  serum  into  mice.  Its  excretion  in  the  urine  is 
questionable.  Tetanus  produces  no  characteristic 
anatomic  changes,  although  degenerative  lesions 
in  the  ganglionic  cells  occur.  Death  usually  occurs 
from  asphyxia  caused  by  contractions  of  the  dia- 


mm. 


414  INFECflON     AND     IMMUNITY. 

phragm^  or  muscles  of  the  glottis,  or  from  cardiac 
failure.  In  some  instances  the  blood  has  been 
found  more  or  less  laked  because  of  the  action  of 
the  tetanolysin. 
Tetanosp^as-  Tctanus  toxin  (tctauospasmin)  has  a  very 
strong  affinity  for  the  nervous  tissue  of  susceptible 
animals.  This  may  be  demonstrated  in  test-tube 
experiments  in  which  the  toxin  is  mixed  with  an 
emulsion  of  the  nervous  tissue;  the  nervous  tissue 
neutralizes  the  toxin  more  or  less  completely,  as 
determined  by  subsequent  inoculations  of  the  mix- 
ture (Wassermann's  experiment).  It  is  held  by 
certain  authorities  that  the  toxin  attacks  only  the 
nervous  tissue  in  man;  in  some  of  the  lower  ani- 
mals, however,  various  organs,  especially  the  liver, 
have  an  affinity  for  the  toxin. 

The  method  by  which  tetanus  toxin  reaches  the 
central  nervous  system  has  been  the  subject  of 
much  speculation  and  experimentation.  Eecent 
observations  by  Marie  and  Morax  and  by  Eansom 
and  Meyer  show  with  a  great  degree  of  probabil- 
ity that  it  is  absorbed  by  the  end  organs  of  the 
motor  nerves  and  from  there  passes  to  the  gang- 
lionic cells  through  the  axis  cylinders.  This  ab- 
sorption takes  place  very  quickly;  when  the  toxin 
is  given  intravenously  it  disappears  from  the  blood 
in  the  course  of  minutes.  It  has  been  found  in  the 
nerves  within  an  hour  and  a  half  after  subcutane- 
ous injection.  Its  further  transmission  centrally 
occupies  more  time  and,  indeed,  the  investigators 
mentioned  explain  the  rather  long  incubation 
period  of  the  disease  on  the  basis  of  the  time  re- 
quired for  this  transmission.  The  brief  incuba- 
tion period  in  "head  tetanus,"  accordingly,  would 


IMMUNITY  IN   TETANUS. 


415 


depend  on  the  short  distance  the  toxin  is  obliged 
to  travel  to  reach  the  ganglionic  cells. 

Although  the  toxin  appears  not  to  be  taken  np 
by  the  sensory  nerves,  a  painful  form  of  the  dis- 
ease, tetanus  dolorosa  (Meyer),  may  be  pro- 
duced experimentally  by  injecting  the  toxin  into 
the  posterior  roots  of  the  spinal  nerves.  Eoux 
caused  "cerebral  tetanus'^  by  introducing  the  toxin 
into  the  cerebral  tissue;  the  condition  is  charac- 
terized by  absence  of  contractures.  "Local  teta- 
nus/^ in  which  the  muscles  in  the  vicinity  of  infec- 
tion or  inoculation  are  involved  in  contractures,  is 
the  first  symptom  of  tetanus  in  experiment  ani- 
mals; it  rarely  occurs  in  man  except  in  head  teta- 
nus. The  phenomenon  depends  on  the  fact  that 
the  toxin,  being  transmitted  through  the  motor 
nerves,  reaches  first  the  ganglionic  cells  which  cor- 
respond to  the  infected  area. 

According  to  Metchnikoff,  the  only  natural  im- 
munity which  man  possesses  to  tetanus  is  leuco- 
cytic  and  this  may  be  sufficient  to  protect  under 
favorable  conditions.  The  observations  of  Vaillard 
and  Eouget  (cited  above)  support  this  claim.  Sus- 
ceptibility depends  not  only  on  the  presence  of 
suitable  receptors  in  the  nervous  tissue,  but  also 
on  the  degree  of  affinity  which  exists  between 
these  receptors  and  the  toxin.  In  man  and  some 
animals  this  affinity  is  very  great,  whereas  in  fowls 
it  is  weak  and  an  enormous  amount  of  toxin  is  re- 
quired to  cause  tetanus.  A  further  proof  of  this 
weak  affinity  in  non-susceptible  animals  rests  in 
the  fact  that  the  toxin  when  injected  into  the  blood 
remains  unabsorbed  for  a  long  time,  whereas  in 
susceptible  animals  it  disappears  very  quickly.  Ac- 


ImiunnitT' 
In    Man. 


Varieties  of 
Tef  auTis. 


416  INFECTION     AND     IMMUNITY. 

quired  immunity  depends  on  the.  presence  of  anti- 
toxin in  the  circulation. 
Propiiyiactic       Tctanus  autitoxin  is  a  thorough  prophylactic. 

Antitoxin.  This  fact  has  been  heralded  so  extensively  in  re- 
cent years  that  there  can  be  little  excuse  for  ignor- 
ance on  the  part  of  any  physician.  At  the  same 
time,  the  returns  from  the  "Fourth"  show  that  the 
principle  is  not  yet  deeply  imbedded  in  the  medical 
mind.  It  is  quite  certain  that  a  large  percentage 
of  these  fatalities  could  be  prevented  by  two  injec- 
tions of  antitetanic  serum,  one  at  the  time  of  in- 
jury and  a  second  from  five  to  eight  days  later, 
x^n  epidemic  of  puerperal  tetanus  in  an  obstetric 
ward  in  Prague  was  checked  by  prophylactic  injec- 
tions of  the  antitoxin.  In  a  certain  section  of 
France  4,000  horses,  with  injuries  commonly  fol- 
lowed by  tetanus,  received  antitoxin  and  none  de- 
veloped the  disease. 

No  degree  of  efficacy  on  the  part  of  the  anti- 
toxin, however,  justifies  disregard  of  the  surgical 
care  which  the  wound  demands.  From  the  facts 
cited  it  is  clear  that  thorough  and  frequent  disin- 
fection of  the  wound,  free  drainage,  the  removal 
of  all  foreign  and  necrotic  material,  and  the  ac- 
cess of  air  are  measures  of  eminent  importance. 
Punctured  wounds  should  be  opened  up.  Anti- 
toxin, preferably  as  a  powder,  may  be  used  in  the 
wound,  and  the  serum  infiltrated  into  the  adjacent 
tissue. 
Curative       Thc  principles  which  apparently  underly  the  ill 

An«roxi7K  success  of  the  antitoxin  as  a  curative  agent  were 
treated  of  in  Chapter  XXII,  Part  II.  Its  adminis- 
tration as  early  as  possible  after  symptoms  have 
appeared  is  demanded.  After  symptoms  have  ex- 
isted for  more  than  thirty  hours  Behring  main- 


VALUE    OF   ANTITOXIN.  417 

tains  that  there  is  no  hope  of  cure  by  the  subcuta- 
neous route.  Inasmuch  as  forty  hours  or  more  are 
required  for  complete  absorption  from  the  subcuta- 
neous tissue,  intravascular  injection  of  at  least  the 
first  dose  would  seem  to  be  indicated.  Yet  by 
neither  of  these  methods  is  the  most  essential  end 
accomplished,  for  the  antitoxin  does  not  reach  the 
nerves  nor  can  it  be  recognized  in  the  cerebrospinal 
fluid  in  conspicuous  quantities.  The  most  that 
such  injections  accomplish  is  the  neutralization  of 
the  circulating  toxin,  that  which  is  not  yet  on  its 
way  to  the  central  nervous  system  through  the  mo- 
tor nerves.  It  is,  of  course,  important  to  neutral- 
ize the  circulating  toxin  and  it  must  be  done  quick- 
ly, for  in  the  course  of  a  few  hours  the  fatal  quan- 
tity of  toxin  may  have  been  absorbed;  "a  dose  of 
antitoxin  which  would  save  in  the  morning  may 
be  without  effect  in  the  evening.-'^ 

At  the  same  time  it  is  of  greater  immediate  im-  Method  of 
portance  to  neutralize  that  which  has  already  en- 
tered the  peripheral  nerves,  and  if  possible  to  tear 
away  some  of  the  toxin  already  bound  by  the  gang- 
lionic cells.  To  acomplish  this  object,  or  to  at- 
tempt it,  special  procedures  are  demanded.  We 
may  then  consider  the  antitoxic  treatment  as  fol- 
lows: 

First:  The  neutralization  of  the  toxin  which 
has  already  been  absorbed  by  the  peripheral  nerves 
and  spinal  cord  at  a  point  as  near  the  vital  centers 
as  possible.  This  involves  surgical  exposure  of  the 
large  nerves  of  the  part  as  near  the  trunk  as  possi- 
ble and  their  infiltration  with  antitoxin  (Eansom 
and  Meyer),  and  in  desperate  cases  the  infiltra- 
tion of  the  antitoxin  in  the  spinal  cord  in  the 
^dcinity  of  the  medullary  centers.     From  five  to 


Usins  the 
Antitoxin. 


418  INFECTION     A^  D     niMUNJTY. 

fifteen  minims  may  be  injected  into  the  nerve 
trimks  at  a  sitting,  and  the  operation  may  be  re- 
peated on  subsequent  days;  the  needle  should  be 
partially  withdrawn  and  reinserted  in  different  di- 
rections during  the  injection.  Eogers  recommends 
tying  loose  ligatures  around  the  nerves  after  the 
operation  so  that  they  may  be  readily  drawn  up 
and  identified  for  further  injections.  In  order  to 
reach  the  medulla  the  intracerebral  method  of 
Roux  or  that  of  Eogers  may  be  utilized.  Kocher 
has  devised  a  technic  for  the  intracerebral  injec- 
tions. Anterior  to  the  parieto-frontal  suture  and 
to  one  side  of  the  median  line  the  scalp  is  pre- 
pared, and  a  hole  drilled  through  the  skin  and 
skull,  having  its  direction  toward  the  foramen 
magnum.  By  means  of  a  long  needle,  the  ventri- 
cle is  penetrated  and  the  serum,  after  injection, 
finds  its  way  to  the  fourth  ventricle  to  the  imper- 
iled respiratory  and  cardiac  centers;  10  c.c.  may 
be  injected.  Eogers  seeks  to  accomplish  the  same 
end  by  a  different  technic.  He  introduces  the 
needle  between  the  sixth  and  seventh  cervical  ver- 
tebra, punctures  the  cord  deepl}^,  and  injects  from 
20  to  30  minims  at  a  sitting.  Although  there  is 
danger  of  intraspinal  hemorrhage  in  the  proce- 
dure, no  ill  effects  were  noted.  It  has  been  recom- 
mended also  that  the  cerebrospinal  fluid  be  with- 
drawn by  means  of  lumbar  puncture  and  substi- 
tuted by  antitoxin.  Some  physicians  who  have 
used  this  method  report  favorable  results. 

Second:  The  neutralization  of  all  toxin  which 
is  not  yet  bound  by  the  nervous  tissue  or  absorbed 
by  the  motor  nerves.  This  demands  the  infiltra- 
tion of  the  wound  and  surrounding  tissue  with  the 
antitoxin,  and  injection  of  a  sufficient  amount  of 


DOSAGE    OF    TETANUS   ANTITOXIN.         419 

the  serum  into  the  circulation  in  order  that  circu- 
lating toxin  may  be  neutralized.  The  intraneural, 
intraspinal  or  intracerebral  injections  should  al- 
ways be  supplemented  by  subcutaneous  or  intra- 
vascular injections.  The  first  dose  should  be  given 
intravenously,  whereas  subsequent  injections  may 
be  given  subcutaneously.  The  injections  should 
always  be  repeated. 

According  to  Anderson,  the  prophylactic  dose 
of  tetanus  antitoxin  standardized  according  to  the 
official  standard  adopted  by  the  United  States 
Public  Health  and  Marine-Hospital  Service  is 
1,500  units.  As  a  curative  it  should  be  given  in 
doses  of  from  3,000  to  20,000  units,  repeated  dur- 
ing the  course  of  the  disease. 

Agglutination  has  no  practical  significance  for 
diagnostic  purposes.  An  agglutinating  power  has 
been  noted  in  the  serum  on  the  eighth  day.  Ag- 
glutinins may  be  produced  by  immunizing  animals 
(rabbits)  either  with  the  bacilli  or  the  toxin.  Id 
the  latter  case  the  formation  of  the  agglutinin  ih 
due  to  the  presence  of  agglutinogenic  receptors  in 
the  toxin  solution. 

III.   BOTULISM. 

Botulism  is  a  peculiar  form  of  meat  poisoning  Baciiins 
in  which  the  nervous  system  is  involved  princi-  fi*>t"'>n"*i' 
pally.  From  twenty-four  to  thirty-six  hours  after 
the  poisonous  meat  is  eaten  salivation,  ptosis,  dila- 
tation of  the  pupils  and  paralysis  of  the  ocular 
muscles  develop  and  death  from  bulbar  paralysis 
occurs  rapidly  in  from  25  to  30  per  cent,  of  the 
cases.  In  the  event  of  recovery,  convalescence  may 
extend  over  weeks  or  months. 


420  INFECTION     AND     IMMUNITY. 

Infected       The  disease  occurs  especially  in  some  European 
Meats.   (-]jgj-pj(3^g   jj^   which   improperly   preserved   or   raw 

meats  are  eaten.  The  term  "ichthyosismus"  is 
applied  to  a  similar  or  identical  disease  which  is 
caused  in  Russia  by  salted  fish.  In  1895  von 
Ermengem  investigated  a  ham  which  had  caused 
50  cases  of  botulism,  and  isolated  from  it  an  anae- 
robic, spore-forming  bacillus,  which  produces  a 
isoluble  toxin  capable  of  causing  the  entire  symp- 
tom-complex of  the  disease.^  The  organism  pos- 
sesses flagell^,  has  limited  motilit}^,  grows  only  in 
alkaline  media,  and  in  contrast  to  most  pathogenic 
organisms  prefers  a  relatively  low  temperature 
(18-25°  C).  It  is  probably  on  account  of  its 
phj^siologic  activity  at  such  temperatures  that  it 
is  able  to  produce  its  toxin  in  meats  which  have 
been  kept  in  a  cool  place.  It  is  found  in  decom- 
posed ham  and  various  sausages  (Leberwurst  and 
Blutwurst),  and  probably  gains  access  to  the  meat 
after  the  animal  has  been  killed.  Von  Ermen- 
gem investigated  two  hams  from  the  same  animal. 
One  was  under  anaerobic  conditions  being  covered 
with  brine,  while  the  other  was  exposed  to  air; 
only  the  former  was  toxic.  The  organisms  may  be 
absent  from  the  superficial  portion  of  the  meat, 
but  abundant  in  the  deep  portion.  The  spores  are 
relatively  susceptible  to  heat,  being  destroyed  by 
a  temperature  of  80°  C.  for  one  hour.  Aside  from 
its  occurrence  in  meat,  nothing  is  known  of  the  life 
history  of  the  bacillus. 
Toxin.  The  disease  is  caused  by  the  toxin  which  has  al- 
ready been  produced  in  the  meat  and  not  by  the 

1.  other  pathogenic  organisms,  especially  B.  entei-itidis 
and  B.  coli  communis,  and  recently  the  paratyphoid  bacil- 
lus, have  been  found  in  poisonous  meats.  The  term 
botulism  formerly  was  applied  to  various  forms  of  meat 
poisoning. 


BOTULISM    TOXIN.  421 

activity  of  the  organism  after  it  has  reached  the 
alimentary  tract  (v.  Ermengem).  If  an  extract 
of  the  meat  is  made  with  water  and  the  bacteria 
removed  from  the  latter  by  filtration,  the  fluid 
shows  characteristic  toxicity  for  animals.  This 
experiment  may  be  used  for  determining  the  pres- 
ence of  botulism  toxin  in  suspected  meat.  The 
guinea-pig  is  the  most  susceptible  animal. 

According  to  v.  Ermengem,  the  bacillus  does  not 
proliferate  in  the  body,  nor  does  it  produce  toxin 
vigorously  at  body  temperature;  hence,  he  consid- 
ers it  to  be  a  strict  saprophyte — a  pathogenic  sap- 
rophyte. 

The  toxin  is  taken  up  by  the  circulation  from 
the  alimentary  tract  and  is  not  destroyed  by  the 
gastric  and  pancreatic  juices,  differing  in  this  re- 
spect from  the  toxins  of  diphtheria  and  tetanus. 
It  is  prepared  artificially  by  growing  the  organism 
anaerobically  in  suitable  bouillon  and  subsequently 
sterilizing  the  fluid  by  filtration.  Like  the  other 
soluble  bacterial  toxins,  it  is  susceptible  to  the  ac- 
tion of  air  and  light,  and  is  destroyed  by  a  tem- 
perature of  from  60  to  70°  C. 

That  the  toxin  has  a  special  afiinity  for  the  nerv-  patbosenesi* 
ous  tissues  is  evident  from  the  symptoms  of  the 
disease;  histologically,  the  ganglionic  cells  show 
degeneration  in  fatal  cases.  Further  evidence  of  a 
strong  aflinity  between  the  toxin  and  nervous  tissue 
lies  in  the  ability  of  the  latter  to  neutralize  the 
toxin  in  the  test-glass.  The  toxin,  however,  ap- 
pears not  to  be  so  selective  in  its  action  on  the 
nervous  tissue  as  the  toxin  of  tetanus,  for  in  bot- 
ulism degenerations  of  the  glandular  organs,  and 
of  the  vascular  endothelium  with  consequent  hem- 
orrhages   are    characteristic     anatomic     findings. 


422  INFECTION     AND     IMMUNITY. 

Man  appears  to  be  very  susceptible  to  the  intoxica- 
tion, whereas  dogs,  rats,  and  cats  are  relatively  im- 
mune. The  toxin  is  pathogenic  by  subcutaneous  or 
intravascular  injection. 

According  to  v.  P]i-mengem,  the  l)acilli  when  in- 
oculated subcutaneously  do  not  proliferate,  but  are 
taken  up  by  the  phagocytes  immediately  or  after 
they  have  been  carried  to  other  organs.  Animals 
which  have  recovered  from  infection  or  which  have 
been  immunized  acquire  rather  strong  immunity 
to  subsequent  inoculations,  the  immunity  being 
antitoxic. 
Prophylaxis  The  proplivlactic  measures  consist  in  the  avoid- 
*"*^  toxin'  ance  of  poorly  preserved  and  improperly  cooked 
meats,  especially  sausages.  Botulism  would  seem 
to  be  very  rare  in  this  country  where  raw  meats 
are  not  used  extensively. 

The  antitoxin  (Kempner)  has  proved  of  some 
value  in  animal  experiments,  but  its  commercial 
preparation  has  not  been  warranted  on  account  of 
the  rarity  of  the  disease. 

IV.   BACILLUS   PYOCYANEUS. 

Pathogenic  For  a  loug  time  it  was  thought  that  the  "bacillus 
roperties.  ^^  |^-^^^  pus"  was  of  no  importance  as  an  infectious 
agent  for  man,  although  its  pathogenicity  for  ani- 
mals had  been  recognized  experimentally.  It  is 
found  with  some  frequency  in  the  blood  and  or- 
gans of  man  at  autopsy,  when  death  has  resulted 
from  some  other  infection  or  chronic  disease,  and 
in  such  instances  it  is  supposed  that  a  so-called 
"agonal  invasion"  by  the  organism  has  occurred. 
During  recent  years,  however,  several  cases  of  pri- 
mary p3^ocyaneus  septicemia  have  been  observed, 
the  bacillus  having  been  obtained  from  the  blood 


BACILLUS  PYOGYANEUS. 


423 


in  pure  cultures  during  life  or  from  the  blood  and 
organs  shortly  after  death.  It  has  been  found  as 
the  sole  organism  in  meningitis  and  vegetative  en- 
docarditis. Some  of  the  cases  indicate,  however, 
that  a  previous  lowering  of  resistance,  as  that 
caused  by  tuberculosis  and  syphilis,  is  important 
for  general  invasion  by  the  bacillus.  It  has  been 
found  several  times  in  suppurative  processes  in  the 
middle  ear,  and  would  seem  to  be  either  the  cause 
or  a  strong  adjuvant  in  some  cases  of  severe  enter- 
itis, especially  in  childern.  In  systemic  infec- 
tions, the  symptoms  are  typhoidal  in  character, 
with  high  temperature,  diarrhea  and  a  tendency 
to  the  formation  of  hemorrhages  in  the  skin  and 
internal  organs. 

The  Bacillus  pyocyaneus  is  widely  distributed 
and  that  it  causes  so  few  infections  is  probably  due 
to  its  low  pathogenic  power.  It  is  an  organism  of 
manifold  activities.  It  produces  a  substance,  pyo- 
cyanin,  which,  when  exposed  to  the  air,  assumes  a 
bluish  tint,  and  on  which  the  color  of  the  pus  de- 
pends; pyocyanin  is  soluble  in  chloroform,  from 
which  it  may  be  precipitated  in  crystalline  form. 
Under  proper  conditions  the  organism  also  forms 
a  fluorescent  pigment.  It  produces  a  strong  pep- 
tonizing ferment,  coagulates  milk,  and  in  old 
cultures  an  autolytic  ferment  is  found  which  di- 
gests many  of  the  bacilli.  As  stated  in  a  previous 
chapter,  Emmerich  and  Lowe  have  identified  a 
bacteriolytic  ferment,  pyocyanase,  which  dissolves 
the  anthrax  bacillus  and  other  organisms.  The 
ferment  nature  of  this  substance  is  in  some  doubt, 
inasmuch  as  it  resists  the  boiling  temperature. 
Dietrich  thinks  its  action  is  due  to  the  production 
of  osmotic  chano-es.     Old  cultures  contain  a  hemo- 


Its  Manifold 
Activities. 


Ferments. 


424  INFECTION     AND     IMMUNITY. 

lytic  agent  (pyocyanolysin)  of  an  alkaline  nature, 
which  resists  boiling  and  is  not  a  true  toxin,  since 
immunization  with  it  does  not  yield  an  antitoxin 
Toxin  and  (Jordau).  In  addition  to  the  ppoducts  mentioned. 
Antitoxin,  ^^iq  oTgauism  secretcs  a  true  soluble  toxin  for 
which  it  is  possible  to  obtain  an  antitoxin,  and 
possesses,  furthermore,  an  endotoxin  for  which 
an  antitoxin  can  not  be  obtained. 

The  soluble  toxin  of  Bacillus  pyocyaneus  is  not 
produced  in  large  amounts.  It  differs  from  the 
other  soluble  toxins  in  its  resistance  to  heat,  with- 
standing a  temperature  of  100°  C.  for  five  min- 
utes. It  produces  the  symptoms  which  are  char- 
acteristic of  infection  with  the  living  organism, 
the  principal  anatomic  changes  being  parenchyma- 
tous degenerations  and  ecchymoses,  the  latter  sup- 
posedly being  due  to  degenerative  changes  in  the 
endothelium  of  the  vessels. 
Antitoxic  and  By  immunizing  with  young  cultures  grown  on 
^*^*ser^m^!  ^u  agar  surface,  a  serum  which  is  bactericidal 
and  opsonic  is  obtained.  On  the  other  hand, 
if  an  older  toxin-containing  bouillon  culture  be 
used,  the  serum  is  opsonic,  bactericidal  and 
antitoxic.  The  serum  which  is  bactericidal  and 
opsonic  has  no  power  of  neutralizing  the  toxin. 
The  toxin  solution  contains  not  only  the  true 
toxin,  but  also  quantities  of  endotoxin  which 
were  liberated  as  the  dead  bacilli  were  dissolved. 
Inasmuch  as  the  antitoxin  neutralizes  only  the 
true  toxin,  leaving  the  endotoxin  unbound,  the 
toxicity  of  the  filtrate  cannot  be  destroyed  entirely 
by  antitoxin,  a  condition  which  is  brought  out 
clearly  when  the  attempt  is  made  to  neutral- 
ize a  multiple  of  the  simple  fatal  dose  by  the 
corresponding  amount  of  antitoxin.    In  such  mul- 


OTHER   TOXINS.  425 

tiples    a   fatal    amount   of   endotoxin    is   present.  . 
Although  a  strong  antitoxin  may  be  obtained^  it 
would  appear  to  be  of  little  practical  importance 
because  of  the  rarity  of  infections  by  the  bacillus. 

Infection  in  man  has  caused  the  formation  of  Aggriutina- 
agglutinin  in  several  instances,  but  it  has  been 
absent  in  others.    An  agglutinating  serum  is  read- 
ily produced  by  artificial  immunization. 

V.  OTHER  SOLUBLE  BACTERIAL  TOXINS. 

Soluble  toxins,  of  perhaps  secondary  impor- 
tance, which  are  produced  by  the  staphylococcus 
and  streptococcus,  will  be  considered  in  the  sections 
dealing  with  these  organisms.  It  seems  probable 
that  they  do  not  represent  the  essential  toxic 
agents  of  the  cocci,  but  rather  that  the  toxicity  of 
the  latter  depends  chiefly  on  the  action  of  endo- 
toxins. 

B.   INTOXICATIOISr  BY  SOLUBLE   PLANT   TOXINS. 
I.    HAY  FEVER. 

Dunbar  separated  from  the  pollen  of  various 
grains  a  toxin  which  is  able  to  precipitate  typical 
attacks  of  hay  fever  in  those  who  are  susceptible, 
having  first  denionstrated  that  the  crude  pollens 
cause  the  disease.  The  pollen  from  the  following 
are  said  to  contain  the  toxin :  Eye,  barley,  wheat, 
maize  (corn),  dog's  tail,  couch-grass,  millet,  rice 
and  some  others.  The  so-called  autumn-catarrh 
which  is  common  in  America  may  be  due  to  a 
slightly  different  toxin  coming  from  the  golden- 
rod,  rag-weed,  and  perhaps  other  autumnal  flower- 
ing grains. 

The   toxin   usually   is    associated   with   certain  TUe  Toxin. 
starch-like  granules  which  are  contained  in  the 


426  INFECTION     AND     IMMUNITY. 

pollen,  but  it  occurs  also  in  pollens  which  do  not 
contain  these  granules.  It  may  be  extracted  with 
^  water  or  salt  solution,  is  precipitated  by  alcohol, 
resists  the  boiling  temperature,  and  is  of  an  al- 
buminous nature. 

When  the  crude  pollen  reaches  the  conjunctiva, 
Pathogenesis,  nasal  or  broncliial  mucous  membranes  of  suscep- 
tible individuals,  the  toxin  is  dissolved  out  by  the 
secretions  and  absorbed  by  the  lymphatics.  When 
applied  to  the  conjunctiva  it  causes  swelling,  red- 
ness and  lachrymation.  It  is  carried  by  the  tears 
to  the  nose  and  here  causes  excessive  secretion, 
swelling  of  the  mucous  membrane  and  sneezing. 
It  may  become  distributed  systemically  as  a  result 
of  absorption  from  the  free  surfaces  and  cause  the 
asthmatic  attacks  and  general  symptoms  which  are 
seen  in  the  intoxication.  When  injected  subcuta- 
neously  into  the  arm  both  the  asthmatic  attacks 
and  coryza-like  symptoms  were  produced. 
Antitoxic  Duubar's  antitoxic  serum  (pollantin)  is  ob- 
rpoiiantin).  taiucd  by  immunizing  horses  with  the  toxin.  It 
seems  to  be  of  undoubted  value  in  a  certain  per- 
centage of  cases,  but  fails  unaccountably  at  times. 
It  is,  perhaps,  most  effective  when  used  in  the 
prodromal  stage,  the  attacks  being  thereby  pre- 
vented. Its  failure  in  certain  instances  may  be 
due  in  part  to  the  inefficacy  of  the  antitoxin 
against  the  toxins  of  certain  pollens.  Again,  in 
certain  individuals  the  affinity  of  the  toxin  for 
the  tissues  may  be  unusually  great  so  that  a  more 
vigorous  use  of  the  remedy  is  demanded. 

Liibbart  and  Prausnitz  published  statistics  of 
285  cases,  of  which  65  were  autumnal.  In  ordi- 
nary hay-fever  the  serum  gave  positive  results  in 
57  per  cent.,  partially  positive  in  32  per  cent,  and 


POLLANTIN.  427 

negative  results  in  11  per  cent,  of  the  cases.  In 
autumnal  catarrh,  70  per  cent,  were  positive,  19 
per  cent,  partially  positive,  and  11  per  cent,  nega- 
tive. 

The  small  bottles  of  antitoxin  are  accompanied 
by  a  pipette  with  which  from  one  to  several  drops 
may  be  instilled  into  the  eye  or  the  nose. 

The  serum  does  not  cure  permanently  and  one 
who  is  susceptible  should  carry  a  vial  for  imme- 
diate use  during  the  hay-fever  season.  Eepeated 
use  of  this  serum  has  been  observed  to  result  in 
sensitization  of  the  patient  to  horse  serum.  Dun- 
bar recommends  in  these  cases  that  a  very  dihitc 
solution  be  used. 

Inhalations  of  increasing  amounts  of  pollen, 
beginning  with  very  minute*  quantities,  has  also 
been  tried  with  the  idea  of  active  immunization. 

It  is  probable  that  further  study  of  hay  fever 
as  a  phenomenon  of  anaphylaxis  will  result  in  the 
explanation  of  points  concerning  the  disease  which 
are  not  yet  clear. 

II.    OTHER  PLANT  TOXINS. 

Ricin,  from  the  seeds  of  Ricinus  communis; 
abrin,  from  Ahrus  lorecatorius;  crotin  from  the 
seeds  of  Croton  tiglium;  and  robin,  from  the  leaves 
and  bark  of  the  locust  tree  (Rohinia  pseudoacacia) 
are  chiefly  of  experimental  interest.  They  are 
similar  in  their  action,  are  very  toxic  to  animals, 
producing  both  local  and  general  changes  with 
fatal  termination  when  given  in  sufficient  doses; 
they  have  pronounced  agglutinating  action  on  the 
erythrocytes  of  most  animals,  and  in  some  in- 
stances are  slightly  hemolytic.  By  guarded  im- 
munization antitoxins  may  be  obtained  for  them. 


428  INFECTION     AND     IMMUNITY. 

Kobert  gave  the  name  of  pliallin  to  a  toxic  sub- 
stance which  may  be  extracted  from  poisonous 
mushrooms,  particularly  the  "Deadly  Amanite" 
{Amanita  phalloides).  In  some  countries  many 
deaths  are  caused  by  eating  this  variety:  Eussia, 
Germany,  Italy,  France,  Japan  (Ford).  Phallin 
is  very  toxic  for  animals  and  is  strongly  hemolytic 
for  many  bloods.  By  immunization  Ford  has  re- 
cently obtained  an  antitoxin  which  neutralizes  the 
hemol3'tic  action  of  the  poison,  and  which  in  a  dose 
of  0.5  c.c.  protects  rabbits  against  five  fatal  doses 
of  the  toxin.  The  toxin  is  an  aqueous  extract  of 
the  dried  plants. 

C.    INTOXICATION  BY  SOLUBLE  ANIMAL  TOXINS. 
I.   POISONING  BY  SNAKE  BITES. 

The  poison  apparatus  of  snakes  consists  of 
a  secretory  gland  on  each  side  which  communi- 
cates with  a  tubular  fang  by  means  of  a  duct.  In 
the  passive  state  the  fangs  are  directed  backward 
on  the  roof  of  the  mouth,  but  when  the  animal 
strikes  their  points  are  made  to  project  forward 
and  the  poison  is  forced  through  the  canals  by 
muscular  compression  of  the  sac.  The  venom  is 
a  glandular  secretion.  The  colubridinae,  among 
which  is  the  American  coral  snake,  possess  im- 
movable fangs. 

The  venoms  of  different  snakes  vary  a  great 
deal  in  their  toxic  properties.  The  most  impor- 
tant constituents  are  those  which  attack  the  nerv- 
ous system  (neurotoxin),  the  blood  corpuscles 
(hemolysins  and  hemagglutinins)  and  the  endo- 
thelium of  the  blood  vessels,  causing  hemorrhages 
(hemorrhagin,  an  endotheliotoxin).  The  three  are 
independent. 


SNAKE    VENOM. 


429 


The  neurotoxin  causes  death  by  paralysis  of  the 
cardiac  and  respiratory  centers.  The  hemolysin 
appears  to  be  of  less  importance  as  a  cause  of 
death. 

The  venoms  of  the  cobra,  water-moccasin,  da-  variations 
boia  and  some  poisonous  sea-snakes  are  essentially  properties 
neurotoxic,  although  they  have  strong  dissolving  fo^ii^T^^' 
powers  for  the  erythrocytes  of  some  animals.  In 
studying  the  hemolytic  powers  of  the  venoms  of 
cobra,  copperhead  and  rattlesnake,  Flexner  and 
Noguchi  found  cobra  venom  to  be  the  most  hemo- 
lytic and  that  of  the  rattlesnake  the  least.  They 
attribute  the  toxicity  of  rattlesnake  poison  chiefly 
to  the  action  of  hemorrhagin.  The  same  authors 
studied  the  action  of  different  venoms  on  the  cells 
of  various  animals  and  by  absorption  experiments 
found  independent  cytotoxins  for  the  testis,  liver, 
kidney  and  blood.  Not  only  was  there  a  distinct 
cytotoxin  for  each  organ  of  an  animal,  but  also 
for  the  same  organ  of  different  animals,  results 
which  speak  for  a  remarkable  complexity  of 
venom.  Certain  venoms  contain  a  leucocytic 
toxin. 

That  venoms  contain  proteolytic  ferments  is 
shown  by  their  ability  to  digest  gelatin  and  fibrin. 
This  power  may  be  related  to  the  softening  of  the 
muscles  which  has  been  noted  clinically  in  cases  of 
poisoning.  The  rapid  decomposition  of  the  body 
which  follows  death  by  snake-poisoning  is  asso- 
ciated with  a  decrease  in  the  bactericidal  power  of 
the  blood,  which,  according  to  Flexner  and  No- 
guchi  depends  on  fixation  of  the  complement  by 
the  venom. 

The  hemolysin  and  neurotoxin,  and  perhaps 
other  cytolysins  of  venom,  consist  of  amboceptors 


Ferments. 


430        •       INFECTION     AND     IMMUNITY. 

Amboceptors  which  in  themselves  are  non-toxic;  they  become 
*"  rnent.  toxic  onlj  thioiigh  the  aid  of  complements  which 

are  present  in  the  bod}^  of  the  poisoned  animal. 
In  this  instance,  complement  which  usually  is  a 
source  of  protection  becomes  a  source  of  danger  to 
the  animal  possessing  it.  Not  only  does  ordinar^y 
serum-complement  serve  for  activation,  but  Kyea 
discovered  that  cells  (erythrocytes)  may  contain 
another  kind  of  complement,  an  "endocomple- 
ment,"  which  activates  the  amboceptors  after  the 
latter  have  combined  with  the  cells.  Flexner  and 
Noguchi  found  that  this  also  was  the  case  with 
the  neurotoxic  amboceptors. 

The  ability  of  lecithin  to  activate  the  hemolytic 
amboceptors  of  cobra  venom  and  the  preparation 
of  cobra-lecithid  (Kyes)  were  described  in  Part  II, 
Chapter  XVI.  In  the  preparation  of  cobra-leci- 
thid the  neurotoxin  is  separated  from  the  hemo- 
lysin, the  former  remaining  in  solution,  whereas 
the  latter  settles  as  a  precipitate  in  combination 
with  the  lecithin.  Immunization  with  the  neuro- 
toxin isolated  in  this  way  causes  the  formation 
of  a  specific  antineurotoxin  (Elliot).  The  neuro- 
toxin may  also  be  abstracted  from  the  venom  by 
treatins^  the  latter  with  the  nervous-  tissue  of  a 
susceptible  animal  (Flexner  and  Noguchi). 

The  hemol3^sin  is  distinct  from  the  hemagglu- 
tinin and  the  latter  may  be  eliminated  by  heating 
the  venom  to  from  75°  to  80°  C.  In  the  action  of 
venom  on  erj^throcytes  agglutination  precedes  he- 
molysis. 
Toxoids  and  The  toxius  may  be  converted  into  toxoids  by 
AntiveniuH.  j^^^^  ^^  treatment  with  chemicals.  Immunization 
with  toxoids  causes  the  formation  of  antitoxins. 


SNAKE    VENOM.  431 

Radium  is  said  to  destroy  the  toxicity  of  venom 
(Physalix). 

The  antivenin  of  Calmette  is  obtained  by  im- 
munizing horses  with  a  mixture  of  venoms  (80 
per  cent,  cobra,  20  per  cent,  viperine  venom)  which 
are  attenuated  before  injection.  Six  months  are 
required  to  produce  a  strong  serum.  The  claim 
of  Calmette  that  his  serum  is  effective  against  all 
snake-venoms  is  erroneous.  It  neutralizes  those 
venoms  the  toxicity  of  which  depends  largely  on 
neurotoxins  and  hemolysins,  but  has  little  influ- 
ence on  rattlesnake  poison,  the  essential  toxin  of 
which  is  hemorrhagin.  Antivenin  for  the  rattle- 
snake and  water-moccasin  may  be  prepared  by  im- 
munization with  the  corresponding  venoms  which 
have  been  attenuated  by  weak  acids.  Noguchi  has 
produced  serum  of  such  strength  that  it  promises 
to  be  of  practical  value  in  the  treatment  of  rattle- 
snake bites. 

As  indicated  previously,  the  action  of  venom  is 
preceded  by  no  appreciable  incubation  period; 
hence,  an  antitoxin  to  be  effective  must  be  admin- 
ister(id  not  later  than  a  few  hours  after  the  bite 
has  occurred.  Noguchi  found  in  relation  to  anti- 
venin for  the  rattlesnake  that  the  quantity  of  anti- 
toxin necessary  to  save  was  quadrupled  three  hours 
after  intravenous  injection  of  two  fatal  doses  of 
v-enom.  Eortunately  the  venom  is  less  toxic  when 
introduced  subcutaneously. 

II.    OTHER   ZOOTOXINS. 

Phrynolysin,  which  is  present  in  the  blood  and 
skin  of  certain  toads,  has  been  studied  especially 
by  Proscher.   It  is  a  thermolabile,  hemol3^tic  toxin 


432  INFECTION     AND     IMMUNITY. 

for  which  an  antitoxin  can  be  obtained  by  immuni- 
zation. 

Arachnolysin,  obtained  from  the  bodies  of  cer- 
tain spiders,  is  a  hemolytic  toxin,  which  by  immun- 
ization yields  a  specific  antitoxin. 

A  poison,  with  properties  resembling  those  of 
snake  venom,  may  be  obtained  from  the  caudal 
segment  of  the  scorpion.  Antitoxin  is  produced 
by  immunization. 

Ichthyotoxin,  a  name  given  to  the  toxic  proper- 
ties of  eel  serum,  is  composed  of  a  neurotoxic  and 
a  hemotoxic  constituent. 

From  the  poisonous  glands  of  certain  fish 
(Trachinus  draco)  a  highly  toxic,  thermolabile 
substance  is  obtainable,  for  which  an  antitoxin  can 
be  prepared  by  the  immunization  of  rabbits 


CHAPTER  XXV. 
GEOUP  II. 


Acute  infectious  diseases  caused  by  bacteria 
which  do  not  secrete  strong  soluble  toxins  in  cul- 
ture media,  but  which  contain  endotoxins  (toxic 
protoplasm).  Infection  or  immunization  causes 
immunity  of  considerable  or  prolonged  duration. 
In  active  immunity  the  serums  agglutinate  the 
corresponding  organisms  and  are  protective  for 
other  animals^  (anti-infectious),  but  have  little  or 
no  curative  power.  The  formation  of  antitoxins 
is  not  definitely  established.  In  most  instances 
vaccination  has  been  accomplished.  Clinically 
there  is  leucocytosis  in  some  instances  and  hypo- 
leucocytosis  in  others  (typhoid  and  Malta  fever). 

A.  The  serum  in  acquired  immunity  is  increased 
in  bactericidal  and  opsonic  power. 

I.   TYPHOID  FEVER. 

Eberth  first  saw  Bacillus  typhosus  in  micro- 
scopic preparations  of  the  mesenteric  lymph  glands 
and  spleen  of  a  typhoid  patient,  in  1880.  Koch 
also  observed  it  at  about  the  same  time,  and 
stained  it  in  the  intestinal  wall,  spleen,  liver  and 
kidney.  It  was  obtained  in  pure  culture  by  Gaffk}- 
in  1884. 

The  organism  is  rod-shaped,  0.5  to  0.8.  by  from 
1  to  3  microns  in  dimensions,  with  nothing  char- 
acteristic in  its  morphology.    It  possesses  from  ten 

1.  This  has  not  been  estabUshed  in  regard  to  Malta  fever. 


434  INFECTION     AND     IMMUNITY. 

to  twelve  flagella  situated  at  the  ends  and  on  the 
sides  and  is  actively  motile  under  suitable  condi- 
tions. It  forms  no  spores  and  is  readily  cultivated 
on  many  media. 

The  bacillus  is  one  of  the  rather  numerous  "in- 
testinal group"  of  organisms^  certain  members  of 
which  are  so  similar  that  they  can  be  differentiated 
only  by  means  of  special  cultures,  animal  experi- 
ments, or  the  agglutinating,  opsonic  and  bacteri- 
cidal action  of  specific  immune  serums.^ 
Distribution  The  orgauism  has  been  cultivated  from  earth 
Bacillus,  and  infected  water,  and  from  the  feces,  urine, 
blood,  rose-spots  and  the  various  organs  of  typhoid 
patients.  In  many  instances  in  which  an  epidemic 
has  certainly  been  caused  b}^  an  infected  water  sup- 
ply attempts  to  cultivate  the  bacillus  from  the 
water  have  failed.  The  organisms  may  not  have 
been  included  in  the  samples  which  were  analyzed, 
or,  w^hat  is  equally  probable  in  certain  instances, 
they  have  died  out  in  the  water  by  the  time  the 
disease  was  so  widespread  as  to  be  considered  epi- 
demic. Its  occurrence  in  Mature  depends  on  the 
distribution  of  the  excretions  of  the  patients  and 
carriers.  The  viability  and  virulence  of  the  bacil- 
viabiiity  lus  in  watcr,  earth,  etc.,  vary  with  the  nature  of 
Resistance,  its  surrouudiugs.  It  lias  been  found  to  live 
for  periods  of  from  2  to  4  weeks  to  2  or  3 
months  in  water,  from  3  to  4  months  in  milk, 
from  3  to  5  months  in  surface  water,  and  from 
11  to  16  months  in  sterilized  earth;  100  days 
in  ice,  from  12  to  30  days  in  oysters,  from  50  to 

2.  Of  this  group  the  bacilli  of  dysentery,  paratyphoid 
bacillus,  liacillus  enteritidis  of  Gartner,  colon  bacillus  and 
lincillus  ah-Mligenes,  In  addition  to  the  typhoid  bacillus,  are 
the  most  important  because  of  their  similar  morphologic  and 
cultural  properties  and  the  pa  thogenlclty  of  certain  of  them. 


E^ndotoxin. 


BACILLUS     TYPHOSUS.  435 

80  days  when  dried  on  clothing,  and  for  3  months 
in  typhoid  feces.  When  in  water  or  moist  earth 
which  contain  many  saprophytes  its  life  is  short- 
ened. It  survives  drying  for  many  months,  al- 
though direct  sunlight  kills  in  the  course  of  a  few 
hours. 

That  the  typhoid  bacillus  secretes  a  soluble 
toxin,  has  not  been  satisfactorily  demonstrated.  It 
contains,  however,  an  endotoxin  which  may  be 
obtained  in  solution  by  the  autolytic  digestion  of 
cultures,  by  extracting  ground-up  bacilli  or  by 
squeezing  out  the  plasma  under  high  pressure.  Up 
to  the  present  time,  immunization  with  none  of 
these  preparations  has  resulted  in  the  production 
of  an  antitoxic  serum  of  accepted  value. 

Typhoid  fever  may  become  epidemic  either  ^^?J®^^.g 
through  a  contaminated  water  and  food  supply  or 
by  contact  infection.  When  due  to  infected  water 
there  is  something  characteristic  about  the  explo- 
sive-like suddenness  with  which  dozens  or  even  hun- 
dreds are  stricken  within  a  short  period.  The  water 
of  streams,  small  lakes  or  reservoirs  may  become 
infected  from  an  ill-constructed  out-house,  or  from 
discharges  which  have  been  thrown  on  the  ground 
in  their  vicinity.  Typhoid  stools  thrown  on  the 
ground  adjacent  to  wells  have  caused  small  epi- 
demics. Fruit,  vegetables  and  milk  cans  may  be 
infected  by  washing  them  with  contaminated  water, 
and  it  is  supposed  that  the  disease  may  be  acquired 
from  oysters  which  have  lain  in  water  contami- 
nated with  sewage. 

The  importance  of  the  so-called  bacillus-carriers 
as  a  source  of  epidemics  of  typhoid  has  been 
recently  emphasized  by  a  great  many  observers. 


436  INFECTION     AND     IMMUNITY. 

Park  estimates  that  from  2  to  5  per  cent,  of  all 
people  who  recover  from  typhoid,  continue  to 
excrete  typhoid  bacilli  by  way  of  the  urinary  or 
alimentary  tracts.  Park  also  estimates  that  one 
out  of  every  500  adults  who  have  never  had 
typhoid,  harbor  typhoid  bacilli.  The  bile  is  gen- 
erally regarded  as  the  medium  in  which  the  bacilli 
perpetuate  themselves  in  the  case  of  the  carriers. 

By  whatever  means  an  apidemic  is  set  in  motion 
primarily,  it  is  usually  aggravated  and  prolonged 
by  the  occurrence  of  contact  infections  (indirect 
contact).  The  hands  of  the  nurse,  physician,  or 
others  who  come  in  contact  with  the  patient  be- 
come contaminated  from  the  stools,  urine,  soiled 
linen  or  skin  of  the  patient,  and  the  organisms 
subsequently  are  transferred  to  food,  drinking 
water,  or  in  other  accidental  ways  reach  the  mouth. 
Each  new  case  is  a  fresh  focus  from  which  infec- 
tion may  be  carried  to  others,  and  the  chances  of 
milk  and  food  infection  become  greater  as  the 
cases  multiply.  When  the  discharges  are  not  dis- 
infected or  are  improperly  disposed  of,  soil  or 
house  infection  may  occur  and  the  possibility 
of  transmission  by  germ-laden  dust  becomes  of 
importance.  Dust  infection  from  dried  urine 
or  feces  and  drop  infection  from  urine,  water, 
or  the  sputum  of  the  patient  are  theoretical- 
ly possible,  but  would  seem  to  be  of  minor  sig- 
nificance. That  flies  may  carry  the  organisms 
from  open  vaults  or  cesspools  and  deposit  them  on 
food  or  in  drinking  water  has  been  appreciated 
in  epidemics  in  military  camps  and  elsewhere. 
Typhoid  bacilli  have  been  cultivated  from  flies 
which  were  taken  from  the  vicinity  of  infected 
material. 


INFECTION     ATRIUM.  437 

The  bacilli  gain  access  to  the  body  through  Tiie  infec- 
the  lymphoid  tissue  of  the  intestinal  tract  (Pey- 
er's  patches  and  the  solitary  follicles).  The  occur- 
rence of  primary  infection  of  the  lungs  through 
inhalation  of  infected  dust  is  possible,  but  has 
not  been  definitely  proved.  In  this  instance  typhoid 
bacillemia  might  occur  either  with  or  without 
intestinal  infection.  In  the  latter  case  it  would 
seem  essential  that  some  local  lesion  exist  in 
the  lungs  or  elsewhere  from  which  organisms 
could  constantly  be  supplied  to  the  blood  N'eufeld 
doubts  the  ability  of  the  tyj)hoid  bacillus  to  pro- 
liferate in  the  blood,  because  of  the  strong  bacteri- 
cidal power  of  the  latter,  and  considers  that  infec- 
tion takes  place  through  the  intestines  even  in  cases 
of  "typhoid  without  intestinal  lesions." 

The  incubation  period  is  subject  to  considerable  incubation 
variations.     In  a  series  of  cases  in  which  the  date 
of  exposure  was  known,  62  per  cent,  showed  symp- 
toms in  from  20  to  25  days,  2  per  cent,  in  from  14 
to  20  days,  and  2  per  cent,  later  than  30  days. 

Quickly  following  the  development  of  intestinal  Localization 
lesions,  the  bacilli  reach  the  circulation  by  way  Baciiii. 
of  the  lymphatics,  and  through  the  action  of  the 
bactericidal  constituents  of  the  blood  (amboceptor- 
complement  complex  and  possibly  leucocytes)  they 
are  killed  and  dissolved  in  large  quantities.  It 
is  now  generally  believed  that  only  through  the 
disintegration  of  the  bacterial  cells  are  their  toxic 
constituents  thrown  into  solution  in  the  body,  a 
condition  which  is  necessary  in  order  that  the  tis- 
sues be  injured.  Infection  of  the  blood  stream 
with  living  organisms,  in  the  early  stages  of  the 
disease  and  preceding  relapses,  occurs  in  probably 
all  the  cases. 


438  INFECTION     AND     IMMUNITY. 

Diagnosis  It  is  possible  to  establish  the  diagnosis  of 
cultures,  typhoid  fever  by  cultivating  the  bacilli  from  the 
bloody  even  before  the  serum  has  developed  suffi- 
cient agglutinating  power  to  cause  agglutination. 
A  small  flask  of  bouillon  is  inoculated  with  from 
1  to  5  c.c.  of  blood,  drawn  from  the  median  vein 
of  the  arm,  and  after  twenty-four  hours  of  incu- 
bation a  small  portion  of  it  is  plated  out.  Colonies 
which  develop  on  the  plates  may  be  identified  by 
the  usual  bacteriologic  methods,  or  the  agglutina- 
tion test  may  be  performed  w^ith  a  known  anti- 
typhoid serum.  After  from  the  tenth  to  the  four- 
teenth day  the  organisms  can  rarely  be  cultivated 
from  the  blood;  the  bactericidal  substances  and 
phagocj'tic  power  of  the  blood  may  have  so 
increased  by  this  time  that  circulating  bacilli  are 
killed  rapidly. 

In  from  one-fourth  to  one-third  of  the  cases,  in 
the  third  Aveek.  or  during  convalescence,  the  bacilli 
appear  in  large  numbers  in  the  urine,  in  which 
they  may  persist  for  many  weeks.  According  to 
Kanjajeff,  they  are  discharged  into  the  urine  from 
metastatic  foci  in  the  kidneys. 

Many  of  the  symptoms,  complications  and  se- 
quelae of  typhoid  fever,  as  the  rose-spots,  enlarged 
spleen,  bone  lesions,  and  in  some  instances  nervous 
lesions  and  pneumonia,  depend  on  the  distribution 
of  the  bacilli.  This  is  in  contrast  to  the  conditions 
in  diphtheria  and  tetanus,  in  which  the  distribu- 
tion of  the  bacilli  is  of  little  significance  for  the 
involvement  of  particular  organs.  The  anatomic 
changes  and  clinical  symptoms  suggest  that  the 
lymphoid  tissue  and  central  nervous  system  have 
a  special  affinity  for  the  toxic  constituents  of  the 
typhoid  bacilli. 


CHANGES  IN  INTESTINAL  LYMPH  NODES.   439 
The  greatest  chan2;es  take  place  in  the  organs   Endotiieiiai 

°  .          1        1        'TT  ,  Hyperplasia. 

(lymphoid)  which  contain  the  bacilli  most  con- 
stantly and  in  the  greatest  numbers.  It  is  here 
that  the  toxic  substance  may  be  present  in  greatest 
concentration,  as  a  consequence  of  the  continual 
solution  of  the  organisms.  Mallory  describes  an 
enormous  hyperplasia  of  the  endothelial  cells,  es- 
pecially those  of  the  lymphatic  structures.  The 
cells  are  phagocytic,  and  especially  in  the  lymphoid 
tissue  of  the  intestines  and  in  the  mesenteric 
lymph  glands,  englobe  and  destroy  the  lymphoid 
cells  on  a  large  scale.  It  seems  probable  that  the 
endothelial  proliferation  which  has  been  described 
is  due  to  the  rather  mild  but  prolonged  action  of 
the  dissolved  toxic  constituents  of  the  typhoid  ba- 
cillus; the  condition  is  that  of  an  inflammatory 
hyperplasia.  It  has  been  suggested  that  the  hypo- 
leucocytosis  of  typhoid  fever  is  due  to  the  destruc- 
tion of  the  lymphocytes  in  the  lymphoid  organs  by 
the  endothelial  phagocytes. 

The  granular  and  fatty  degenerations  of  the 
parenchymatous  organs  do  not  differ  from  those 
seen  in  many  acute  infections. 

The  conditions  in  the  intestinal  tract  would  3iixed_ 
seem  to  favor  mixed  infections,  especially  by  the 
colon  bacillus  and  streptococcus,  and  the  primary 
infection  probably  decreases  the  resistance  to  sec- 
ondary invasion.  The  role  of  the  colon  bacillus  in 
typhoid  fever  is  perhaps  not  definitely  established, 
although  it  has  been  found  in  the  circulation,  in 
abscesses,  and  in  the  urine  in  cases  of  cystitis  ac- 
companying the  disease.  The  typhoid  and  colon 
bacilli  grow  well  together.  A  mixed  general  in- 
fection with  the  streptococcus  causes  a  grave  sep- 
tic condition  characterized  by  an  irregular  tem- 


440  INFECTION     AND     IMMUNITY. 

perature  curve.    This  condition  may  be  discovered 
by  blood  cultures.    It  is  thought  that  the  strepto- 
coccus does  not  increase  the  toxicity  of  the  typhoid 
bacillus,  the  result  being  rather  a  summation  of 
the    intoxication    of    the    two    infections.     Post- 
typhoidal  suppurations  are  often  due  to  the  strep- 
tococcus and  in  many  of  the  metastatic  complica- 
tions   (parotitis,  pleurisy,  peritonitis,  meningitis, 
otitis  media)   streptococci  and  staphylococci  have 
been  found.     Pneumococcus  pneumonia  not  infre- 
quently complicates  typhoid  fever.     A  combined 
infection  of  typhoid  and  malaria  is  said  to  occur  in 
the  tropics;  the  complication  is  grave.     Typhoid 
and  diphtheria  may  occur  together,  and  typhoid 
may  be  superimposed  on  acute  tuberculosis. 
Immunity      The  period  of  greatest  susceptibility  to  typhoid 
^""^  UMifty:  is  found   from  the   fifteenth   to   the  twenty-fifth 
years.     The  resistance  of  infants  and  children  is 
not  satisfactorily  explained.    A  certain  amount  of 
resistance  inherited  from  the  mother  may  persist 
for  some  years  after  birth.    It  is  kno^vn  that  anti- 
bodies  may  pass  from  the   mother  to  the   fetus 
through  the  placenta.  In  very  early  life  the  tissues 
may  respond  more  energetically  to  incipient  in- 
fection by  the  rapid  formation  of  typhoid  anti- 
bodies, or  the  phagocytic  cells  may  be  more  active. 
The  conditions  which  render  older  people  less  sus- 
ceptible are  no  better  understood.    A  loss  of  suit- 
able receptors  may  have  occurred  so  that  the  toxic 
constituents  of  the  bacilli  find  no  anchorage  in  the 
body,  or  the  affinity  between  the  receptees  and  the 
toxic  constituents  may  have  become  less.    The  in- 
dividual during  the  course  of  years  may  have  been 
gradually    immunized   by   the   entrance    of    non- 
pathogenic quantities  of  the  bacilli  into  the  cir- 


IMMUNITY     TO     TYPHOID  441 

culation.  That  resistance  to  typhoid  infection  is 
decreased  by  low  nutrition  and  overwork  is  a  long- 
known  fact. 

A  large  amount  of  protection  is  afforded  by  the  ^lc*™^?^^"^ 
hydrochloric  acid  of  the  gastric  jiiice,  and  it  is  immunity. 
reasonable  to  believe  that  suppression  or  an  insuf- 
ficient amount  of  hydrochloric  acid  may  favor  the 
passage  of  living  bacilli  to  the  intestines.  Normal 
human  serum  is  rather  strongly  bactericidal  for 
the  typhoid  bacillus,  and  the  leucocytes  ingest  and 
destroy  it.  Metchnikoff  ascribes  natural  immun- 
ity to  the  action  of  the  microphages. 

The  immunity  which  follows  an  attack  of  Duration  of 
typhoid  fever  is  generally  of  long  duration,  but  immunity. 
second  attacks  occur  with  some  frequency.  Accord- 
ing to  Dreschfeld's  figures  0.7  per  cent,  of  individ- 
uals are  affected  twice.  It  has  been  noted  that 
limited  communities  which  have  experienced  an 
epidemic  may  remain  relatively  free  from  the  dis- 
ease over  a  period  of  some  years,  although  neigh- 
boring districts  are  attacked.  All  the  susceptible 
persons  having  had  the  disease,  a  state  of  temporary 
immunity  is  created. 

Acquired  immunity  is  characterized  by  an  in- 
crease of  the  bactericidal  amboceptDrs,  opsonins, 
agglutinins  and  typhoid  precipitins  in  the  serum. 
It  has  been  shown  that  recovery  is  accompanied  by 
an  increase  in  concentration  of  antibodies.  Bac- 
tericidal amboceptors  reach  a  concentration  two  or 
three  times  that  of  normal  serum  and  then  return 
gradually  to  normal,  reaching  a  normal  concentra- 
tion in  a  few  months.  Opsonins  increase  in  con- 
centration as  do  bactericidal  amboceptors,  but 
remain  high  for  many  months.  Stone  believes  that 
this   increased   power   of  phagoc3^tosis   constitutes 


442  INFECTION     AND     IMMUNITY. 

the  most  important  factor  in  the  immunity  result- 
ing from  an  attack. 

This  is  not  clear  from  the  clinical  standpoint 
because  of  the  hypoleucocytosis  which  is  some- 
what characteristic  of  typhoid — a  hypoleucocytosis 
caused  chiefly  by  a  disappearance  of  the  micro- 
phages.  It  has  been  suggested  that  our  con- 
clusions as  to  hypoleucocytosis  are  based  on  ex- 
amination of  the  peripheral  blood,  whereas  the 
mesenteric  vessels  may  show  hyperleucocytosis. 
Mallory,  however,  found  a  striking  absence  of 
microphages  even  in  the  intestinal  vessels.  Con- 
cerning a  theory  that  the  hyperplasia  of  the  lym- 
phoid organs  serves  as  a  substitute  for  the  hyper- 
leucocytosis, we  may  recall  the  findings  of  Mallory 
that  this  hyperplasia  is  chiefly  one  of  endothelial 
cells.  The  importance  of  these  endothelial  cells 
for  the  destruction  of  typhoid  bacilli  needs  further 
im'estigation. 
propiiyiaxis.  Prophylaxis  should  begin  with  the  thorough 
disinfection  of  the  stools  and  urine  of  typhoid  pa- 
tients, and  this  should  be  continued  until  they  no 
longer  contain  typhoid  bacilli.  It  is  not  good 
hygiene  to  discharge  a  patient  until  bacteriologic 
examination  of  stools  and  urine  show  them  to  be 
free  from  the  organisms.  It  would  be  difficult  to 
carry  out  this  rigid  precaution  under  all  condi- 
tions, but  at  all  events  the  stools  and  urine  may  be 
disinfected  for  a  reasonable  period,  say  through- 
out convalescence.  There  is  no  sufficient  reason 
for  the  neglect  of  the  bacteriologic  examination  in 
hospital  practice.  There  is  a  growing  sentiment 
that  typhoid  patients  in  hospitals  should  be  iso- 
lated in  wards  or  rooms  in  which  there  is  a  fixed 
routine  for  the  disposal  of  infectious  materials — 


THERAPY.  UZ 

urine,  stools  and  sputum.  Soiled  linen,  the  bath 
water  of  typhoid  patients,  the  remnants  of  food 
and  drink,  and  the  eating  ntensils  should  be  dis- 
infected before  removal  from  the  room.  Nurses 
or  attendants  should  not  eat  or  drink  in  typhoid 
rooms. 

Hexamethylenamin  may  be  of  value  in  causing  Hexamethyi- 
the  disappearance  of  bacilli  irom  the  urine,  and 
the  advisability  of  using  the  drug  as  a  routine 
measure  for  public  safety  is  worthy  of  con- 
sideration. The  room  should  be  kept  free  from 
flies  and  eventually  it  should  be  disinfected,  pref- 
erably by  formalin.  During  an  epidemic,  in  case 
the  water  supply  of  a  community  is  susceptible  to 
contamination,  all  water  used  for  drinking,  wash- 
ing of  vegetables  and  eating  utensils,  should  be 
boiled,  and  that  used  for  general  cleaning  may  be 
otherwise  disinfected.  The  possibility  of  dust  in- 
fection of  a  house  should  not  be  disregarded. 

The  typhoid  carrier  remains  one  of  the  difficult 
problems  of  prophylaxis.  That  carriers  may  be 
rid  of  bacilli  by  inoculation  with  dead  bacilli,  has 
not  been  satisfactorily  demonstrated  except  in 
some  instances.  Systematic  detection  and  treat- 
ment of  these  carriers  is  hard  to  carry  out. 

There  are  two  methods  of  specific  prophylaxis  serotherapy 
against  typhoid:  1,  the  injection  of  antityphoid  tu*n. 
immune  serum;  2,  preventive  inoculation  with 
killed  cultures  of  the  bacilli.  Antityphoid  serum 
confers  a  fairly  strong  and  immediate  immunity 
which,  however,  is  of  short  duration,  because  of 
the  rapid  elimination  of  the  serum.  Its  use  as  a 
general  preventive,  therefore,  is  not  advocated. 

Wright  has  been  influential  in  showing^  the  util-  AVrigriit* s 

p  ..  ,,.  -jif'T        -rx-       Metliod  and 

ity  of  protective  inoculations  against  typhoid.    His  Results. 


444  INFECTION     AND     IMMUNITY. 

first  experimental  work  was  published  in  1896. 
Since  that  time  the  inoculations  have  been  carried 
on  extensively  in  Bristish  regiments  in  India  and 
South  Africa.  The  occurrence  of  typhoid  among 
tlie  inoculated  was  one-half  that  among  the  unin- 
oculated,  and  the  inoculations  reduced  the  mor- 
tality of  the  disease  by  one-half.  The  protection, 
so  far  as  known,  lasts  for  two  or  more  years,  al- 
though in  some  instances  infection  has  occurred  in 
The  Vaccine,  from  three  to  six  months  after  vaccination. 

The  methods  of  preparation  of  the  vaccine  are 
elaborate  in  order  to  insure  sterility  and  standard- 
ization. Cultures  of  the  bacillus  are  grown  in 
bouillon  for  from  twenty-four  to  forty-eight 
hours,  and  then  sterilized  at  60  C.  The  contents 
of  several  flasks  are  mixed  in  order  to  obtain  a 
uniform  distribution  of  organisms,  and  standard- 
ization is  then  accomplished  by  estimating  the 
number  of  bacilli  in  a  cubic  centimeter  of  the  vac- 
cine. The  purity  is  insured  by  bacteriologic  tests, 
and  for  preservation  phenol  or  liquor  cresolis  com- 
positus  is  added. 

Wright  has  abandoned  his  original  method  of 
giving  a  single  injection  and  now  recommends  two 
moderate  doses,  which  are  given  from  eight  to 
fourteen  days  apart.  The  first  dose  includes  a 
quantity  of  vaccine  which  contains  from  750,000,- 
000  to  1,000,000,000  of  bacilli,  the  second  1,500,- 
000,000  to  2,000,000,000.  Wright  finds  that  "the 
inoculation  of  these  quanta  induces  an  ample 
elaboration  of  antibodies  without  producing  any 
severe  constitutional  reaction."  The  inoculations 
increase  the  bactericidal,  opsonic  and  agglutinating 
powers  of  the  serum  and  it  is  concluded  that  an 
increased    resistance    to    typhoid    intoxication    is 


THERAPY.  445 

established  because  the  second  injection  causes 
mikler  symptoms  than  the  first.  The  phagocytic 
power  of  the  leucocytes  is  raised,  because  of  an 
increase  in  the  ''opsonins."  The  curve  of  the  anti- 
bodies is  like  that  usually  obtained  by  active  immu- 
nization with  bacteria,  toxins  or  other  substances. 
Immediately  following  the  inoculation  there  is  a 
decrease  even  of  normal  antibodies.  This  "nega- 
tive phase/'  according  to  Wright,  lasts  for  from 
one  to  several  days  and  corresponds  to  a  period  of 
increased  susceptibility.  Eussell  and  others  have 
not  observed  this  period  of  increased  susceptibility. 
It  is  quickly  followed  by  a  positive  phase  in  which 
the  antibodies  and,  correspondingly,  the  resistance, 
increase  rapidly.  When  very  small  doses  are 
administered  the  positive  phase  may  be  recognized 
after  twenty-four  hours  (Wright).  Large  doses 
cause  a  prolonged  negative  phase  and  are  to  be 
avoided. 

Following  injection,  ''the  local  symptoms  first  ^^^^^ 
make  themselves  felt  after  an  interval  of  two  or  Reactions. 
three  hours.  The  effects  then  seen  are  the  develop- 
ment of  a  red  blush  and  more  or  less  serous  exuda- 
tion at  the  site  of  inoculation,  followed  by  some 
lymphangitis  along  the  lymphatics  which  lead,  ac- 
cording as  the  vaccine  has  been  inoculated  above 
or  below  the  middle  line  of  the  trunk,  in  the  direc- 
tion of  the  glands  of  the  axillae  or  of  the  groin. 
.  .  .  Even  severe  inflammation  has  never  led  on 
to  suppuration.''  The  exudate  is  somewhat  hem- 
orrhagic, and  the  pain  varies  from  moderate  to 
severe,  but  is  not  of  long  duration.  With  the 
technic  as  recommended  at  present,  "the  constitu- 
tional symptoms  are  limited  to  some  headache  and 
to  two  or  three  hours  of  real  malaise.    .    .    .    Tne  Reaction. 


446  INFECTION     AND     IMMUNITY. 

next  day  his  temperature  comes  down  to  normal, 
and  he  feels  comparatively  well  except  in  respect 
to  pain  at  the  seat  of  inoculation."  Of  5,473  sol- 
diers vaccinated  against  typhoid,  twenty-one  took 
the  disease  and  two  died.  In  6,610  soldiers  under 
similar  conditions  who  were  not  vaccinated,  there 
were  187  cases  and  twenty-six  deaths  (Leish- 
mann).  The  m.cthod  of  vaccination  used  by  Eus- 
sell  and  his  associates  in  the  U.  S.  Army  is  similar 
to  that  of  Wright,  but  three  injections  ten  days 
apart  are  given,  the  first  of  500  million,  the  second 
and  third  of  one  billion.  No  bad  results  have 
occurred  in  8,510  cases,  and  the  results  have  been 
satisfactory,  not  a  single  case  of  typhoid  occurring 
ill  any  one  whose  vaccination  was  completed. 
Among  the  unprotected  in  the  army  200  cases 
developed  in  the  same  period  of  time. 

The  vaccine  was  prepared  as  follows:  A  non- 
virulent  strain  of  the  bacillus  is  grown  on  agar^ 
slanted  in  flasks  for  twenty-four  hours.  The 
growth  is  then  emulsified  in  salt  solution  and 
standardized  to  contain  1  billion  bacilli  to  1  c.c. 

The  vaccine  is  then  sterilized  by  heating  to  56° 
C.  for  one  hour;  0.25  per  cent,  tricresol  is  added 
as  a  preservative  and  the  sterility  tested  by  aerobic 
and  anaerobic  cultures.  The  harmlessness  is  proved 
by  inoculation  into  guinea-pigs  and  mice. 
conditioiiN  The  adoptiou  of  antityphoid  inoculation  or  vac- 
Vaccination^  ciuation  uudcr  certain  conditions  appears  to  be 
warranted.  Typhoid  never  has  been  a  world  pest; 
but  in  the  presence  of  epidemics  in  densely  popu- 
lated districts,  the  method  may  well  be  considered. 
The  question  is  a  pertinent  one  also  for  those  cities 
in  which  typhoid  is  so  extensive  as  to  be  called 
endemic.     It  has  a  distinct  field  in  the  protection 


THERAPY.  447 

of  troops  in  time  of  war,  when  it  is  difficult  to 
observe  other  proph3'lactic  measures,  and  should 
recommend  itself  to  physicians  and  nurses  during 
epidemics. 

The  products  of  autodigestion  of  typhoid  cul- 
tures have  been  suggested  as  suitable  vaccine 
(Neisser  and  Shiga).  The  local  reaction  is  said 
to  be  mild,  and  the  body  reacts  by  the  formation 
of  bactericidal  amboceptors  and  agglutinins. 

Bactericidal  serums  obtained  by  the  immuniza-  serotherapy. 
tion  of  horses  with  typhoid  bacilli  have  not  shown 
distinct  curative  properties.  Chantemesse  im- 
munizes horses  with  a  typhoid  "toxin''  which  is 
prepared  by  growing  the  organism  in  a  liquid  cul- 
ture which  contains  an  emulsion  of  splenic  tissue. 
One  cubic  centimeter  of  this  toxin  will  kill  a 
guinea-pig,  a  dose  which  in  comparison  with 
other  bacterial  toxins  is  very  weak.  Chantemesse 
has  used  his  antitoxic  serum  in  the  treatment  of 
more  than  500  patients,  reporting  a  mortality  of 
about  6  per  cent.,  whereas  that  among  untreated 
patients  was  from  10  per  cent,  to  12  per  cent. 
Although  these  figures  indicate  some  value  for  the 
serum,  it  has  had  little  trial  outside  of  France. 

MacFadyen  and  Eowland  immunize  horses  with 
extracts  of  typhoid  bacilli,  which  have  been  ground 
up  while  they  w^ere  kept  in  a  brittle  state  by  the 
temperature  of  liquid  air.  Although  antitoxic  and 
bactericidal  properties  are  claimed  for  the  serum, 
there  is  no  conclusive  evidence  that  it  differs  from 
bactericidal  serum  prepared  in  the  ordinary  way. 

Jez  produces  a  high  degree  of  immunity  in  rab-  Preparation 
bits  by  artificial  immunization  with  the  typhoid 
bacillus,  then  prepares  an  extract  from  the  spleen, 
bone  marrow,  brain,  etc.,  of  the  immunized  ani- 


448  INFECTION     AND     IMMUNITY 

mals.  The  extract  is  administered  by  mouth.  Jez 
justifies  this  method,  from  the  fact  that  the  lym- 
phoid organs  have  been  shown  to  form  typhoid 
antibodies  (Wassermann).  From  the  clinics  of 
Eichorst  and  others  favorable  reports  concerning 
the  remedy  have  been  published.  It  has  had  no 
extensive  use.  The  preparation  is  made  by  the 
Serum  Institute  of  Berne  and  is  expensive.  The 
suggestion  of  Fraenkel,  that  typhoid  patients  be 
treated  by  subcutaneous  injections  of  small  quan- 
tities of  killed  typhoid  bacilli  in  order  to  hasten 
the  formation  of  antibodies  has  been  kept  alive 
through  the  "typhoin"  of  Petruschky,  but  has  not 
had  practical  trial.  Of  a  similar  nature  is  the  sug- 
gestion of  Eichardson,  that  the  filtrates  of  typhoid 
cultures  be  injected.  Eichardson  reports  unsatis- 
factory results  with  various  preparations  of  typhoid 
bacilli,  including  the  non-toxic  split  products  of 
Vaughan. 

Anders  has  concluded  from  his  results  following 
the  injections  of  killed  typhoid  bacilli,  that  the 
procedure  is  of  value  only  in  cases  of  relapse  and 
in  bacillus-carriers  in  order  to  rid  the  person  of 
the  bacilli.  Doses  of  from  25  to  50  million  bacilli 
were  used  and  the  injections  were  repeated  every 
three  days. 
Agsintina-  The  principles  and  technic  of  the  agglutination 
****"•  test  were  described  in  Part  T.  The  serum 
commonly  becomes  agglutinating  on  from  the 
seventh  to  the  tenth  day,  rarely  as  early  as  the 
second  or  third,  and  as  late  as  from  the  twentieth 
to  the  fortieth  day.  The  power  is  highest  during 
convalescence,  when  it  may  agglutinate  in  dilu- 
tions as  high  as  1  to  5,000  or  higher,  and  from 
that    time    sinks    gradually.      An    agglutinating 


PARATYPHOID. 


441) 


power  of  1  to  160  has  often  been  found  at  eight 
months,  and  of  1  to  50  after  from  seven  and  one- 
half  to  eleven  years;  but  the  latter  duration  is  not 
the  rule.  In  performing  the  test,  a  serum  dilution 
of  not  ]es  than  1  to  40,  or  1  to  50  should  be 
observed  as  previously  set  forth. 

The  following  sources  of  error  are  to  be  borne 
in  mind :  Typlioid  fever  occasionally  runs  its 
course  without  the  formation  of  agglutinins;  the 
reaction  may  mysteriously  be  absent  one  day  to 
recur  a  few  days  later,  a  condition  which  indicates 
the  importance  of  repeated  tests;  rather  high  ag- 
glutinating power  for  the  typhoid  bacillus  occa- 
sionally develops  in  other  infections,  as  pneumo- 
nia, meningitis,  icterus,  Weil's  disease,  etc. ;  the 
possibility  of  group  agglutination,  for  the  positive 
elimination  of  which  control  tests  with  related  or- 
ganisms may  be  demanded.  In  case  negative 
results  are  obtained  in  a  suspicious  case,  the  reac- 
tions should  be  tried  with  the  paratyphoid  bacilli. 
The  test  of  the  bactericidal  powers  of  the  serum 
has  been  recommended  as  a  substitute  for  the  ag- 
glutination reaction,  but  the  technic  is  so  much 
more  complicated  that  the  method  will  probably 
not  come  into  general  use.  For  diagnosis  previous 
to  the  formation  of  agglutinins,  blood-cultures 
should  be  made  as  described  in  a  preceding  para- 
graph. 

II.    PARATYPHOID  FEVER. 

In  1900  Scholtmiiller  cultivated  from  the  blood 
of  five  "typhoid''  patients  organisms  which  differ  Paratyphoid 
from  the  typhoid  bacillus  in  that  they  attack  dex-  ^paracolon" 
trose  with  gas  formation  and  are  not  agglutinated  Baciiii. 
in   high    dilution    by    antityphoid    serum.      Since 


450  INFECTION     AND     IMMUNITY. 

then,  similar  cases  have  been  reported  and  two 
types  of  the  paratyphiod  bacillus  have  been  recog- 
nized (Schottmiiller).  Bacilli  of  Group  B  cause 
first  an  acid  reaction  in  milk  which  changes 
to  a  permanently  alkaline  reaction  in  about  ten 
days,  whereas  those  of  Group  A  cause  permanent 
acidity  (Kayser).  They  resemble  the  typhoid 
bacillus  morphologically,  but  culturally  are  more 
closely  related  to  Bacillus  enteritidis.  Organisms 
which  have  previously  been  described  as  "para- 
colon'^  bacilli  (Widal,  Gwyn)  do  not  differ  from 
those  which  are  now  called  paratyphoid  bacilli, 
and  the  infections  caused  by  them  resembled  the 
recorded  cases  of  paratyphoid  fever.  The  term 
"paracolon"  should  no  longer  be  applied  to  them. 
Paratyphoid  fever  occurs  sporadically  or  in  epi- 
oiogry.  demic  form,  and  bears  a  close  resemblance  to  mild 
typhoid-like  epidemics  which  have  been  noted  from 
time  to  time,  and  which,  presumably,  are  caused 
by  eating  poisonous  meats.  One  such  epidemic  of 
600  cases  was  caused  in  Switzerland  in  1878  by 
the  meat  of  a  sick  calf;  the  mortality  was  1  per 
cent.  A  still  older  epidemic  (1839)  is  cited,  like- 
wise caused  by  meat.  In  both  instances  the  infec- 
tion eventually  was  carried  from  person  to  person 
by  contact.  A  recent  outbreak  in  Kiel,  proved  to 
be  paratyphoid,  is  assumed  by  Fischer  to  have  been 
caused  by  infected  meat,  on  account  of  the  peculiar 
distribution  of  the  cases  among  the  patrons  of  a 
particular  market.  Kurth  also  attributed  a  small 
epidemic  to  either  uncooked  meat  or  milk.  Fischer 
mentions  fifty  cases  in  East  Holstein  probably 
caused  by  the  milk  of  two  cows.  Shortly  after  the 
epidemic  began,   the   cows   died   and   paratyphoid 


Epidemi- 


PARATYPHOID. 


451 


bacilli  were  cultivated  from  the  muscles,  spleen, 
liver  and  intestines.  De  Feyfer  cites  an  instance 
in  which  the  disease  apparently  was  transmitted 
through  the  water  of  a  stream  in  which  the  cloth- 
ing of  the  first  patients  had  been  washed.  In 
another  instance,  a  regimental  infection  was  traced 
to  the  discharges  of  a  single  soldier,  the  water  sup- 
ply having  become  contaminated  through  a  defec- 
tive water  closet. 

Paratyphoid,  like  tvphoid  fever,  is  accompanied  cuaracter- 

1  1        T  J  -Ai      istics  of  tlie 

Dy  an  enlarged  spleen  and  many  rose  spots.  Ai-  Disease. 
though  severe  symptoms  may  be  present  for  a  time, 
the  course  of  the  disease  usually  is  mild  and  the 
mortality  is  low.  The  incubation  period  approxi- 
mates that  of  typhoid.  In  the  few  cases  which 
have  come  to  autopsy  the  intestinal  lesions  have 
varied  from  a  mild  ileocolitis  with  an  intact  mu- 
cous surface  to  a  condition  of  superficial  ulcera- 
tion. The  involvement  of  Peyer's  patches  and  the 
solitary  follicles  which  is  so  characteristic  of  ty- 
phoid is  absent,  although  these  structures  may  be 
moderately  swollen.  The  mesenteric  lymph  glands 
are  not  markedly  involved  and  there  is  little  pro- 
liferation of  the  lymphoid  or  endothelial  cells 
(Wells  and  Scott).  The  disease  has  no  specific 
anatomic  lesion. 

The  organisms  are  found  in  the  blood  and  vari- 
ous organs,  in  the  rose  spots,  urine  aiid  feces  of  the 
patients.  Practically  nothing  is  known  of  the  oc- 
currence of  the  bacilli  outside  the  body.  Because 
of  their  presence  in  the  stools  and  urine  of  the  pa- 
tients, the  methods  of  dissemination  and  infection 
doubtless  are  similar  to  those  concerned  in  typhoid. 
The  bacillus  is  said  to  have  a  marked  resistance  to 
heat^  withstanding   60°    C.   for   30   minutes   and 


Excretion, 
Resistance 
and  Distri- 
bution. 


452 


INFECTION     AND     IMMUNITY. 


Agrsrlutina- 

tion   and 

Blood 

Cultures. 


not  all  cells  being  killed  during  one  hour  at 
this  temperature.  This  may  explain  the  fact  that 
the  virus  is  not  ahvaj-s  killed  by  cooking  the  meat. 
The  organism  probably  has  a  wide  distribution 
because  of  the  occurrence  of  the  infection  in  vari- 
ous parts  of  the  world. 

The  toxicity  of  the  bacilli  depends  on  the  exist- 
ence of  a  fixed  endotoxin;  a  soluble  toxin  is  not 
produced.  The  principles  of  prophylaxis  against 
typhoid  also  apply  to  paratyphoid  fever,  with  the 
addition  that  in  the  latter  disease  the  possibility  of 
meat  infection  must  be  kept  in  mind. 

The  serums  of  patients  and  immunized  animals 
acquire  bactericidal,  opsonic  and  agglutinating 
powers  for  the  organism.  There  is  no  serum  ther- 
apy for  the  infection,  nor  has  the  occasion  arisen 
to  attempt  vaccination. 

Serum  from  a  paratyphoid  patient  may  aggluti- 
nate the  homologous  bacillus  in  a  dilution  of 
1/1000  or  1/2000  or  more  (E.  H.  Ruediger), 
whereas  the  typhoid  bacillus  is  agglutinated  only 
in  low  dilutions  by  the  same  serum.  How- 
ever, bacillus  A  and  bacillus  B  are  not  identical 
in  their  agglutinable  properties;  in  this  respect 
it  is  stated  that  the  latter  is  more  closely  re- 
lated to  the  typhoid  bacillus  than  the  former. 
The  agglutination  test  is  said  to  have  a  higher 
diagnostic  value  than  the  Gruber-Widal  reaction 
in  typhoid,  a  stronger  agglutinating  power  being 
developed  in  the  serum  of  the  patient.  Never- 
theless, the  formation  of  coagglutinins  may  render 
the  test  confusing  if  proper  serum  dilution  is  not 
practiced.  Conclusions  should  not  be  attempted 
until  the  test  has  been  performed  with  both  strains 
of  the  paratyphoid  bacillus  and  with  the  typhoid 


DYSENTERY     IIAC/LLUS.  453 

bacillus.  As  in  typhoid,  early  diaguosis  may  be 
best  accomplished  by  bacteriologic  examination  of 
the  blood. 

III.    ACUTE    EPIDEMIC    DYSENTERY. 

In  addition  to  amebic  dysentery,  we  have  de- 
come  familiar  with  an  acute  dysenteric  infection 
which  appears  epidemically  in  both  tropical  and 
temperate  climates,  and  prevails  especially  in  the 
summer  months.  Such  epidemics  occur  extensively 
in  Japan,  where  the  mortality  may  be  24  per  cent. ; 
in  the  Philippines,  United  States,  Germany  and 
other  European  countries.  In  industrial  settle- 
ments in  Germany  the  mortality  is  about  10  per 
cent.  (Kruse).  The  incubation  period  may  be  as 
short  as  two  or  three  days.  In  mild  cases  the  pa- 
tient may  recover  in  from  four  to  eight  days, 
whereas  severe  cases  last  from  two  to  four  weeks, 
and  may  terminate  fatally.  Occasionally  the  in- 
fection lasts  sufficiently  long  to  be  considered 
chronic. 

In  1898,  Shiga,  basing  his  conclusions  on  posi-  3^^*5,3^**®*  **' 
tive  results  with  the  agglutination  test  and  on  the 
constant  presence  of  the  organism  in  the  stools  of 
the  infected,  identified  as  the  cause  of  the  disease, 
in  Japan,  a  microbe  which  is  known  as  Bacillus 
dysenterice.  (Shiga).  Flexner,  in  1900,  made  simi- 
lar observations  on  epidemic  dysentery  in  Manila, 
and  his  organisms,  or  one  of  them,  differing  slight- 
ly from  that  of  Shiga,  is  called  Bacillus  dy sentence 
(Flexner),  or  the  Flexner-Harris  bacillus,  Harris 
being  the  name  of  a  patient  from  whom  this 
typical  strain  was  cultivated.  Kruse  (1901)  found 
both  the  Shiga  and  Flexner  types  in  Germany, 
needlessly  giving  the  name  of  ^^pseudodysenterv" 
bacilli  to  the  latter.    In  this  country  similar  organ- 


454 


INFECTION     AND     IMMUNITY. 


Snnimer 
Diarrheas. 


Character- 

IstlcH   of 

the  Bacilli. 


isms  have  been  found  as  the  cause  of  institutional 
dysentery  by  Vedder  and  Duval,  of  summer  diar- 
rheas of  infants  bv  Duval  and  Bassett,  and  bv  Wol- 
stein.  It  is  the  belief  of  Vedder  and  Duval  that 
acute  dysentery,  the  world  over,  "whether  sporadic, 
institutional  or  epidemic,  is  caused  by  the  dysen- 
tery bacillus."  We  must  note,  however,  that  the 
organism  is  not  found  in  all  cases  of  clinical  dys- 
entery, even  by  skilled  bacteriologists.  "Clinically, 
24  of  our  97  cases  in  which  the  dysentery  bacilli 
were  found  did  not  differ  from  the  cases  of  ileocoli- 
tis in  which  the  dysentery  bacilli  were  not  found." 
(Weaver  and  others.)  It  seems  certain,  neverthe- 
less, that  Bacillus  dysenterice  is  the  most  impor- 
tant cause  of  acute  dysentery.  It  rarely  occurs  in 
the  stools  of  healthy  individuals. 

The  organisms  of  Shiga  and  Flexner  differ  in 
their  actions  on  the  sugars  mannite  and  maltose 
(i.  e.,  in  their  acid-forming  powers)  and  in  their 
agglutinability ;  the  "Flexner"  type  is  the  stronger 
acid-former.  An  artificially  produced  immune  se- 
rum which  is  specific  for  one  organism  has  rather 
higher  agglutinating  and  bactericidal  powers  for 
the  corresponding  type,  but  low  for  the  other.  In 
this  country  the  "Flexner"  bacillus  is  much  more 
common  than  that  of  "Shiga,"  but  here  and  abroad 
both  types  are  met,  and  sometimes  in  the  same 
individual.  Several  other  organisms  have  been 
cultivated  from  dysenteric  patients,  but  the  varia- 
tions from  these  two  types  are  slight.  All  are 
certainly  very  closely  related. 

The  organism  is  somewhat  thicker  than  the 
typhoid  bacillus,  but  probably  is  non-motile,  al- 
though Vedder  and  Duval,  in  opposition  to  others 
(Lentz),  claim   to  liavo  deinonstrated  flagella.     It 


DYSENTERY     BACILLUS.  455 

often  shows  a  polymorphous  appearance  in  cul- 
tures, but  forms  no  spores.  It  is  Gram-negative. 
It  lives  for  from  12  to  17  days  when  dried 
(Pfuhl)  ;  direct  sunlight  kills  it  in  30  minutes, 
1  per  cent,  phenol  in  30  minutes,  5  per  cent,  phenol 
plus  colTosive  sublimate  (1/2000)  almost  instan- 
taneously. It  is  thought  that  it  may  live  over 
winter  and  cause  fresh  outbreaks  in  the  spring 
(Kruse). 
The  bacillus  is  found  only  in  the  stools  of  the  P***?:*''^**^'* 

^  in  tlie   Body. 

infected,  in  the  mucous  or  muco-hemorrhagic  por- 
tions of  which  it  exists  almost  in  pure  culture,  few 
colon  bacilli  being  in  the  immediate  vicinity;  it 
has  not  been  found  in  the  blood  or  urine.  In  fatal 
cases,  Shiga  found  it  only  in  the  intestinal  ulcers 
and  swollen  lymphoid  structures  and  in  the  mesen- 
teric lymph  glands.  Flexner  mentions  its  occur- 
rence in  the  liver.  The  organism,  if  it  reaches  the 
circulation  at  all,  either  does  so  in  small  quantities, 
or  is  rapidly  destroyed  by  the  blood.  The  infection 
resembles  cholera,  but  differs  from  typhoid  and 
paratyphoid  in  this  respect.  An  observation  by 
Markwald  (cited  by  Lentz)  indicates,  however, 
that  the  bacilli  may  reach  the  circulation.  A 
woman  ill  with  dysentery  gave  birth  to  a  child, 
which  died  within  a  few  hours.  Dysenteric  changes 
were  found  in  the  intestines,  and  the  bacillus  of 
dysentery  was  cultivated  from  the  diphtheritic  de- 
posits on  the  intestines,  from  the  meconium  and 
from  the  hearths  blood.  The  organisms  must  have 
reached  the  child  through  the  placenta  from  the 
circulation  of  the  mother. 

The  intestinal  lesions  vary  from   a  simple  in-  Lesions. 
flammatory  hyperemia  to  rather  extensive  superfi- 
cial necrosis    (dijihtheritic   inflammation),   which 


Oreanisms. 


456  INFECTION     AND     IMMUNITY. 

rarely  extends  below  the  submucosa.  Such  foci 
are  said  to  be  the  most  marked  in  the  descending 
colon  and  sigmoid  where  mechanical  injury  is 
more  likely  to  occur.  The  necrotic  areas  separate 
by  sloughing,  leaving  superficial  ulcers.  The  lym- 
phoid follicles  are  swollen  and  infiltrated  with 
polymorphonuclear  leucocytes,  which  also  accumu- 
late in  the  dilated  lymph  spaces  of  the  intestinal 
wall.  The  ileum  is  so  commonly  involved  that  the 
condition  is  called  an  ileocolitis.  Conspicuous 
changes  are  not  found  in  the  mesenteric  glands  or 
spleen.  The  liver  and  kidne3^s  commonly  show 
parenchymatous  degenerations. 
Toxicity  of  The  dyscutcry  bacillus  is  highly  toxic.  Subcu- 
taneous injections  of  killed  cultures  produce  in 
man  a  more  profound  reaction  than  the  organism 
of  either  cholera  or  typhoid.  Ordinary  laboratory 
animals  are  so  susceptible  that  they  are  immunized 
with  difficulty;  the  horse  is  less  susceptible.  The 
toxicity  of  the  organism  apparently  depends  on  an 
intracellular  toxin  (an  endotoxin)  rather  than  on 
a  soluble  toxin.  When  living  or  killed  cultures 
are  submitted  to  autodigestion  in  salt  solution 
(Conradi,  Xeisser  and  Shiga),  or  when  bouillon 
cultures  are  allowed  to  grow  for  30  days,  the 
liquids  are  found  to  be  toxic  after  the  organisms 
are  removed.  In  both  instances  this  toxicity  prob- 
ably depends  on  the  liberation  of  endotoxins.  The 
question  as  to  whether  the  bacillus  in  the  intes- 
tines produces  a  soluble  toxin  which  is  absorbed  by 
the  lymphatics,  is  undetermined.  It  seems  more 
probable  that  the  conditions  are  analogous  to  those 
of  cholera,  intoxication  resulting  from  the  libera- 
tion of  endotoxins  by  the  solvent  action  of  the  tis- 
Bue  fluids  or  cells  on  the  bacilli.    Dysenteric  symp- 


PROPHYLAXIS.  457 

toms  are  not  produced  in  animals  by  feeding  the 
organisms. 

The  stools  of  the  patient  are  the  only  known  Dissemina- 
source  of  the  organism  and  it  continues  to  be  ex-  infection. 
creted  during  convalescence.  Latent  or  chronic 
cases  are  a  source  of  danger  to  a  community.  Al- 
though the  conditions  outside  the  body  are  not 
favorable  for  the  growth  of  the  organism,  it  may 
remain  living  and  virulent  for  several  months.  The 
methods  of  infection  appear  identical  with  those 
in  t3^phoid.  Water  infection  seems  certain^  and 
indirect  transmission  is  accomplished  by  contact 
with  the  discharges.  The  best  examples  of  contact 
infection  are  found  in  institutional  epidemics. 

The  first  essential  for  prophylaxis  is  correct  di-  propiiyiaxis 
agnosis,  for  which  the  agglutination  test  and  bac-  triAuty.*^^^' 
teriologic  examination  of  the  stools  are  essential. 
Disinfection  and  other  precautions  should  be  prac- 
ticed as  rigidly  as  in  typhoid.  The  patient  should 
not  be  discharged  until  the  stools  are  free  from 
dysentery  bacilli. 

Poorly  nourished  individuals  are  particularly 
susceptible  to  infection,  and  among  them  the  mor- 
tality is  high.  The  disease  is  most  common  among 
young  children,  old  people,  and  those  who  are  con- 
fined in  institutions.  The  conditions  in  Japan, 
however,  where  from  June  to  December  of  one  year 
nearly  90,000  were  attacked,  and  in  Germany, 
where  severe  epidemics  occur  in  industrial  com- 
munities, indicate  that  susceptibility  is  quite  gen- 
eral. Digestive  disturbances  and  enteritis  from 
other  causes  are  said  to  be  predisposing  factors, 
The  normal  serums  of  man  and  animals  have  very 
little  bactericidal  power  for  dysentery  bacilli. 


458  INFECTION     AND     IMMUNITY. 

The  subject  of  acquired  immunity  to  dysentery 
is  hardly  on  a  satisfactory  basis.  The  serum  of 
convalescents  shows  a  distinct  bactericidal  and  op- 
sonic power  for  the  organism,  and  there  is  good 
reason  to  believe  that  the  acquired  immunity  per- 
sists for  some  time  after  the  disappearance  of  the 
bactericidal  amboceptors  and  opsonins,  an  event 
which  takes  place  rather  early.  As  in  typhoid, 
animals  which  through  immimization  have  once 
been  stimulated  to  produce  antibodirs,  form  them 
much  more  readily  on  the  occasion  of  a  subsequent 
inoculation.  This  acquired  facility  in  producing 
antibodies  ma}^  be  a  factor  in  acquired  immunity. 
By  immunizing  horses,  serums  of  rather  high  pro- 
tective power  have  been  obtained.  Kruse  prepared 
a  serum  of  which  1/80000  gram  would  save  a 
guinea-pig  from  a  dose  of  the  bacilli  which  killed 
a  control  in  20  hours.  It  is  assumed  that  the  pro- 
tective power  of  this  serum  is  due  to  its  bactericidal 
action.  The  antitoxic  serum  which  Rosenthal  pre- 
pared, by  immunizing  with  30  days'  old  bouillon 
cultures,  protected  not  only  against  the  toxin,  but 
also  against  the  bacilli;  and  conversely  an  anti- 
bacterial serum  protected  against  the  toxin  (cited 
by  Lentz).  Such  results  leave  us  very  much  in 
doubt  as  to  the  existence  of  a  true  antitoxic  serum. 
Vaccination       The  valuc  of  protective  inoculations  is  not  well 

and   Serum  ^ 

Therapy,  established.  Shiga  at  one  time  practiced  mixed 
active  and  passive  immunization  (bacilli  plus  im- 
mune serum)  on  10,000  individuals.  This  did  not 
decrease  the  number  of  infections,  although  a  lower 
mortality  resulted.  Shiga  claims  that  the  thera- 
peutic use  of  his  serum  reduces  the  mortality  to 
one-third  that  of  the  untreated.  The  serum  of 
Kruse,  and  also  that  of  Rosenthal,  are  said  to  be 


tion. 


AGGLUTINATION.  459 

curative :  the  discharges  rapidly  decrease  in  number 
and  the  course  of  the  disease  is  shortened.  In  the 
Eockefeller  Institute  for  Medical  Research  anti- 
dysentery  serum  proved  of  no  distinct  value. 

The  agglutination  reaction  with  the  serum  of  Agsiniina- 
patients  shows  great  variability.  It  is  sometimes 
absent  in  spite  of  the  presence  of  bacilli  in  the 
stools,  and  often  disappears  rapidly  during  con- 
valescence (in  two  weeks  occasionally).  It  is  rarely 
as  high  as  in  typhoid.  In  infantile  diarrheas  ag- 
glutinins appear  at  about  the  end  of  the  first  week 
of  illness  (Duval  and  Bassett).  Evidently  mild 
cases  in  which  the  course  of  the  disease  is  from 
four  to  eight  days  may  not  be  recognized  by  means 
of  the  agglutination  reaction  before  the  period  of 
convalescence.  In  chronic  cases  the  agglutinating 
power  may  persist  for  three  or  four  months.  No 
reaction  was  obtained  with  the  typhoid  bacillus. 
Kruse  considers  the  reaction  diagnostic  when  it 
occurs  in  a  dilution  of  1/50 ;  Pfuhl,  1/30.  Strong 
co-agglutinins  for  other  organisms,  i.  e.,  above 
1/50,  have  not  been  observed  (Lentz).  The  tests 
should  always  be  performed  with  both  the  "Shiga^^ 
and  "Flexner'^  types,  as  the  two  have  not  identical 
agglutinable  properties,  and  either  organism  may 
be  the  cause  in  a  given  instance.  The  absence  of 
the  reaction  does  not  exclude  a  dysenteric  infec- 
tion positively.  Bacteriologic  examination  of  the 
stools  is  important,  often  necessary,  for  early  diag- 
nosis. 

IV.    MEAT  POISONING  BY  BACILLUS  ENTERITIDIS. 

Botulism  as  a  special  form  of  meat  poison- 
ing and  the  occasional  production  of  paratyphoid 
by  infected  meats,  have  been  mentioned.  In 
addition  to  these,  more  or  less  extensive  epidemics, 


460  INFECTION     AND     IMMUNITY. 

supposed  to  be  due  to  ptomains  which  were  found 
in  putrid  meat^  have  occurred  not  infrequently. 
It  is  now  Avell  established  that  most  epidemics  of 
this  character  are  caused  by  pathogenic  bacteria 
which  are  present  in  the  meat,  putrid  decomposi- 
tion of  the  latter  being  an  unessential  incident. 
BaciiiuN  Gartner,  in  1888,  had  the  opportunity  of  study- 
mg  an  epidemic  caused  by  the  meat  ot  a  cow  which 
had  been  slaughtered  m  extremis.  The  symptoms 
differed  from  those  of  botulism  or  paratyphoid,  as 
described  below.  He  obtained  from  the  muscle  and 
spleen  of  the  cow,  and  from  the  spleen  of  a  man 
who  had  been  fatally  poisoned,  an  organism  which 
has  since  been  known  as  Bacilhis  enteritidis  (Gart- 
ner). The  same  bacillus,  or  organisms  which  re- 
semble it  closely,  have  been  obtained  repeatedly 
during  similar  epidemics,  both  from  the  suspected 
meat  and  from  the  organs  in  fatal  cases  (intes- 
tines, blood,  spleen,  etc.)..  Drigalski,  from  a  com- 
parative study  of  several  strains  obtained  from  dif- 
ferent sources,  concluded  that  all  are  members  of  a 
closely  related  group  of  organisms,  the  group  of 
Bacillus  enteritidis.  His  conclusions  were  based 
on  cultural  properties  and  agglutination  tests. 

The  typical  organism  is  a  short  rod,  often  ovoid 
in  shape,  possesses  from  four  to  twelve  long  flag- 
ell  a  and  has  moderate  motility.  It  ferments  vari- 
ous sugars  and  is  not  stained  by  Gram's  method. 
Variations  among  individual  strains  need  not  be 
discussed  here. 
i-nUio-  According  to  v.  Ermengem,  and  also  Drigalski, 
its  pathogenicity  depends  on  the  elaboration  of  a 
soluble  but  heat-resistant  toxin.  Bouillon  cul- 
tures twelve  days  old,  in  which  the  bacteria  have 
been   killed   bv   heat,   also   similar   cultures    from 


K''iiicity 


BAVlLLUti     ENTEIilTlDI^.  4G1 

which  the  bacteria  have  been  removed  by  filtration, 
are  toxic  for  mice  and  guinea-pigs  (Drigalski).  It 
is  noteworthy,  however,  that  relatively  large  quan- 
tities of  the  bouillon  were  necessary  to  kill  guinea- 
pigs  (4.0  c.c.)  which  is  in  contrast  to  the  toxins  of 
diphtheria  and  tetanus.  The  rapidity  with  which 
symptoms  develop  following  the  ingestion  of  in- 
fected meat  is  a  further  indication  of  the  exist- 
ence of  this  soluble  toxin,  which,  it  would  seem,  is 
formed  in  considerable  quantities  in  the  meat. 
Symptoms  occasionally  develop  so  quickly  as 
to  suggest  some  strong  metallic  poisoning.  With- 
in a  few  hours  vomiting,  violent  diarrhea  and 
colicky  pains  set  in,  followed  by  more  or  less 
collapse,  weakness,  headache  and  not  uncom- 
monly by  erythematous,  urticarial  or  herpetic 
eruptions.  Fever  is  absent  or  inconspicuous. 
The  mortality  is  not  high,  from  2  to  5  per  cent.; 
convalescence  is  said  to  be  slow.  Nephritis  and 
catarrhal  pneumonia  have  been  noted  as  sequelai. 
Autopsy  shows  the  anatomic  changes  of  an  acute 
gastroenteritis,  sometimes  of  hemorrhagic  charac- 
ter, with  swollen  Peyer's  patches;  the  large  intes- 
tine is  not  greatly  involved.  The  spleen  may  be 
swollen  and  the  kidmeys  degenerated.  The  ana- 
tomic findings  are  not  specific. 

It  has  been  shown  in  numerous  instances  that  sources  of 
the  cattle  or  horses  (Drigalski)  which  furnished 
the  meat  were  sick  with  an  intestinal  or  general 
infection  with  Bacillus  enteritidis  before  they  were 
slaughtered.  "In  a  very  large  number  of  cases  it 
can  be  demonstrated  that  the  animals  from  which 
the  meat  was  taken  had  been  slaughtered  hi 
extremis  or  had  died  recently,  and,  indeed,  that 
thev  had   (in  certain  instances)   died  before  they 


Infection. 


462 


INFECTION     AND     IMMUNITY 


GroT^tli   ill 
tlie  Meat. 


Toxin   in 
Ment. 


could  be  slaughtered.  Most  often  they  suffer  from 
septic  inflammatory  processes  or  from  traumatic, 
puerperal  or  other  sorts  of  septicemia,  or  from 
other  ill-defined  pathologic  conditions  which  are 
accompanied  by  symptoms  of  enteritis  or  intestinal 
or  pulmonary  inflammations"  (v.  Ermengem). 
Subsequent  infection  of  the  meat  by  Bacillus  en- 
teritidis,  i.  e.,  after  slaughtering,  has  not  been 
noted. 

The  organism  occurs  in  the  blood  and  various 
organs  of  infected  animals  and  man.  Poisoning 
most  commonly  arises  when  the  meat  has  been 
kept  for  several  days,  which  usually  is  the  case  by 
the  time  it  is  made  into  some  form  of  sausage.  In 
the  meantime  the  bacilli  have  proliferated  and  ad- 
ditional toxin  has  been  produced.  In  at  least  one 
instance  a  certain  number  of  patients  who  ate  the 
meat  while  it  was  fresh  suffered  moderate  or  no 
intoxication,  whereas  those  who  ate  it  several  days 
later  became  violently  ill.  In  an  epidemic  caused 
by  horse  meat  Drigalski  found  that  "only  those 
persons  suffered  from  intoxication  who  ate  the 
meat  after  it  had  lain  for  eight  days  or  more." 

The  micro-organism  is  very  resistant  to  heat 
and  the  temperature  which  is  attained  in  ordinary 
cooking  may  not  be  sufficient  to  kill  the  bacteria 
which  are  remote  from  the  surface.  Even  in  the 
event  that  the  meat  has  been  thoroughly  sterilized, 
the  heat-resistant  toxin  may  be  present  in  suffi- 
cient quantity  to  cause  the  intoxication.  Not 
much  is  known  concerning  the  distribution  of 
Bacillus  enteritidis.  v.  Ermengem  suspects  that 
it  may  be  a  factor  in  poisoning  by  oysters  and  fish, 
but  this  remains  undetermined. 


COLOIi     BACILLUS. 


463 


The  blood  acquires  specific  agglutinins  during  Agrgriutinins. 

the  course  of  infection.  Even  eight  days  after  the 
beginning  of  symptoms  agglutination  may  be  ob- 
tained in  dilutions  varying  from  1/200  to  1/4000. 
The  agglutinins  disappear  very  rapidly.  Working 
with  artificially  prepared  immune  serum,  Drigal- 
ski  determined  the  existence  of  coagglutinins  for 
typhoid  and  paratyphoid  bacilli. 

AVe  should  bear  in  mind  the  likelihood  that 
meats  poisoned  with  Bacillus  enteritidis,  as  well  as 
by  paratyphoid  bacilli,  may  be  encountered  in 
America,  as  well  as  in  foreign  countries. 

V.   BACILLUS  COLI 

Bacillus  coli,  or  the  colon  bacillus,  is  the  type  of 
a  large  group  of  organisms  the  members  of  which 
show  individual  differences,  but  possess  certain 
dominant  features  in  common.  The  typical  colon 
bacillus  ferments  various  sugars,  with  the  produc- 
tion of  gas,  is  a  strong  acid  producer  and  curdles 
milk.  It  is  fiagellated,  has  moderate  motility  and 
does  not  stain  with  Gram's  method.  One  type  or 
another  is  the  normal  inhabitant  of  the  intestinal 
tract  of  many  animals,  and,  although  the  organ- 
isms are  widely  disseminated  in  nature,  their 
occurrence  is  related  directly  or  indirectly  to  the 
distribution  of  feces. 

Its  optimum  temperature  for  growth  is  37°  C,  Assriutinins. 
and  above  46°  C.  it  does  not  proliferate.  It  is 
killed  at  a  temperature  of  from  60°  to  61°  C.  in 
from  five  to  fifteen  minutes;  it  is  not  killed  by 
such  low  temperatures  as  from  — 20°  to  — 24°  C. 
It  resists  absolute  desiccation  for  periods  varying 
from  a  few  days  to  several  months  (different  ob- 
servers). Direct  sunlight  kills  99  per  cent,  of  the 
germs  in  two  hours  (Billings  and  Peckham),  and 


464 


i:s'fegtio:n   and   immunity. 


Distribution 


they  are  very  susceptible  to  ordinary  antiseptics. 
The  normal  serums  of  many  animals  are  bacterici- 
dal for  the  colon  bacillus. 

Escherich,  the  discoverer  of  this  organism,  lays 
down  the  principle  that  that  strain  which  may 
be  cultivated  from  the  feces  of  the  nursing  child 
should  be  considered  as  the  typical  Bacterium  coli 
commune,  maintaining  that  a  constant  type  of  or- 
ganism is  found  under  these  conditions.  It  is  said 
to  occur  here  in  relatively  pure  culture. 

Within  a  very  short  time  after  birth  the  organ- 
intestines^  ^^^  ^^  found  In  the  intestines  of  infants,  and  its 
method  of  entrance  has  been  the  subject  of  much 
discussion.  In  view  of  its  ready  dissemination  it  is 
not  difficult  to  conceive  of  many  circumstances 
which  favor  its  entrance.  Having  once  reached 
the  intestines,  it  finds  there  its  optimum  conditions 
for  growth.  The  small  intestines  in  man  are 
rather  free  from  colon  bacilli  and  other  organisms 
as  well.  This,  perhaps,  is  due,  to  some  extent,  to 
the  alkalinity  of  the  medium  and  to  the  rather 
rapid  flow  of  the  intestinal  contents  at  this  point. 
The  colon  bacillus  reaches  its  maximum  develop- 
ment in  the  large  intestine,  where,  in  fact,  the 
whole  bacterial  flora  of  the  intestines  is  most  con- 
centrated. 

In  view  of  the  fact  that  the  colon  bacillus  is  a 
normal  inhabitant  of  the  intestines,  the  conception 
has  occurred  to  many  that  it  may  be  of  distinct 
value  to  the  economy,  either  because  of  the  action 
it  has  on  certain  foods  (splitting  of  carbohy- 
drates), or  because  in  some  obscure  way  it  in- 
fluences favorably  the  assimilation  of  foods,  or  in 
that  it  antagonizes  other  bacteria  of  distinct  patho- 
genic powers  which  also  exist  normally  in  the  iu- 


Normal 
Fnnctions. 


FUNCTION    OF    COLON    BACILLUS.  4G5 

testines  or  reach  them  through  accident.  This  is 
not  the  place  to  consider  these  questions  in  detail, 
and  they  are  on  none  too  definite  a  basis.  Tt  may 
be  stated,  however,  that  the  colon  bacillus  and  an- 
other closely  related  organism,  Bacillus  [Iactis~\ 
aerogenes,  distinctly  antagonize  the  action  of  cer- 
tain proteolytic  bacteria  which  appear  to  be  associ- 
ated with  the  putrid  decomposition  of  milk  and 
other  proteid-containing  foods.  Bacteria  of  the 
latter  type  exist  in  the  intestines.  Unsterilized 
milk  has  a  natural  resistance  to  putrid  decomposi- 
tion, and  sterilized  milk  to  which  the  colon  bacillus 
or  Bacillus  \lactis']  aerogenes  has  been  added,  has 
a  similar  resistance.  These  two  bacteria  flourish 
in  the  presence  of  carbohydrates,  which  they 
decompose  with  the  liberal  formation  of  acids,  and 
through  these  acids  they  "limit  intestinal  putre- 
faction and  influence  (favorably)  pathologic  proc- 
esses wdiich  are  caused  or  maintained  by  the 
existing  ^alkaline  fermentation' "  (Escherich  and 
Pfaundler).  That  the  organisms  in  question 
antagonize  the  action  of  putrefactive  bacteria  has 
been  shown  in  test-tube  experiments  (Hirschler). 
Since  the  time  that  v.  Emmerich  upheld  th^ 
colon  bacillus  (or  a  colon-like  microbe)  as  tht 
cause  of  Asiatic  cholera  (1885),  opinion  as  to  the 
pathogenic  powers  of  the  organism  has  undergone 
many  fluctuations.  Following  Koch's  demonstra- 
tion of  the  comma  bacillus  as  the  etiologic  factor 
in  cholera,  the  colon  bacillus  was,  so  to  say,  re- 
pressed as  a  pathologic  agent.  Later,  and  especially 
in  France,  great  significance  was  again  attached  to 
it.  The  condition  still  shows  a  great  deal  of  chaos, 
although,  on  account  of  more  refined  technic  and 
the  elimination  of  other  organisms,  as  the  dvseiv 


Patho- 
genicity. 


466 


INFECTION     AND     IMMUNITY. 


"Virulence 
for  Animals. 


Virnlence 
for    Man. 


tery  and  paratyphoid  bacilli  and  Bacillus  enteritis 
dis,  from  the  colon  group  proper,  we  are,  perhaps, 
on  the  way  to  a  more  satisfactory  understanding 
of  the  pathogenicity  of  this  organism.  Although 
certain  authors  hold  at  the  present  time  that  the 
colon  bacilli  which  normally  inhabit  the  intes- 
tines are  devoid  of  virulence,  such  a  radical  posi- 
tion is  open  to  question.  Avirulent  strains  have 
often  been  encountered,  however. 

Harmless  as  the  colon  bacillus  appears  to  be 
when  confined  in  the  intact  intestines,  its  viru- 
lence for  animals,  although  low,  has  been  demon- 
strated in  many  instances.  A  bouillon  culture  of 
the  average  bacillus  which  has  grown  for  from  one 
to  two  days,  and  when  freshly  cultivated  from  the 
stools,  causes  the  death  of  a  300  to  400  gram 
guinea-pig  in  two  or  three  days,  when  given  intra- 
peritoneally  in  a  dose  of  from  2  to  3  c.c.  Subcu- 
taneous inoculations,  the  feeding  of  cultures,  their 
introduction  into  the  bladder  and  biliary  passages 
induce  inflammatory  processes.  It  is  stated 
(Escherich)  that  whether  the  cultures  are  intro- 
duced into  the  skin,  peritoneum  or  vessels,  symp- 
toms of  severe  gastroenteritis  are  produced,  not 
unlike  Asiatic  cholera.  This  fact  doubtless  in- 
fluenced V.  Emmerich  in  considering  the  organism 
as  the  cause  of  cholera.  The  general  symptoms  are 
those  of  an  acute  febrile  intoxication. 

The  organism  is  most  pathogenic  when  freshlv 
cnltivatcd,  and  soon  loses  its  virulence  after  re- 
peated transplantations.  As  in  the  case  of  some 
other  bacteria,  virulence  may  be  re-established  by 
'^passage"  through  suitable  animals. 

The  cultivation  of  the  colon  bacillus  from  the 
blood  and  organs  of  man  at  autonsv  has  not  the 


COLON     BACILLUS    INFECTIONS.  467 

significance  which  was  once  attached  to  it.  It  has 
been  recognized  that  the  colon  bacillus  in  particu- 
lar, and  less  commonly  other  intestinal  organisms 
may  enter  the  circulation  a  short  time  before  death, 
at  a  time  when  resistance  is  very  low,  and  may 
obtain  the  general  distribution  which  is  so  often 
encountered  at  autopsy;  this  is  the  so-called  "ago- 
nal invasion,"  which  may  occur  without  much  re- 
gard to  the  primary  cause  of  death.  The  condi- 
tions which  favor  agonal  invasion  remain,  to  a 
large  extent,  obscure.  Distinct  defects  of  the  in- 
testinal mucosa  probably  are  not  essential,  al- 
though this  view  has  its  representatives.  In  states 
of  low  vitality  in  which  resistance  to  infection  is 
decreased  (disappearance  of  complement),  the  or- 
ganisms find  conditions  favorable  to  proliferation 
when  they  have  once  reached  the  circulation.  In 
spite  of  the  low  virulence  of  the  colon  bacillus,  it 
commonly  has  a  certain  amount  of  toxicity  and  it 
may  often  be  of  significance  even  as  an  agonal  in- 
fection. 

Post-mortem  invasion  of  adjacent  structures,  as 
the  gall  bladder  and  liver  through  the  biliary  pas- 
sages, and  of  the  peritoneum  through  the  intesti- 
nal wall,  also  occurs. 

It  has  been  shown  that  the  colon  bacillus  occa-  True 
sionally  causes  the  following  conditions :  Suppura- 
tive cholecystitis  which  may  extend  to  the  liver, 
peritonitis,  septicemia,  meningitis,  cystitis,  pyeli- 
tis and  ascending  suppurative  nephritis,  and  ab- 
scesses in  various  organs,  including  suppurative 
processes  in  the  middle  ear.  In  one  or  more  in- 
stances it  has  been  thought  that  it  caused  vegeta- 
tive endocarditis.  Probably  colon  infections  of  the 
gall  bladder  do  not  occur  in  the  absence  of  biliary 


Infections. 


468  INFECTION     AND     IMMUNITY. 

stasis.  Ordinarily  cases  of  peritonitis  in  which 
the  colon  bacillus  is  encountered  also  show  the 
presence  of  other  pathogenic  organisms,  as  strepto- 
cocci or  staphylococci;  this  is  always  the  case  in 
perforation  peritonitis.  Doubtless  wrong  conclu- 
sions have  been  drawn  in  many  instances  as  to  the 
bacteriology  of  peritonitis  from  the  fact  that  the 
colon  bacillus  readily  overgrows  many  other  bac- 
teria in  culture  media. 
Cystitis.  Escherich  attributes  great  importance  to  this  or- 
ganism as  the  cause  of  cystitis,  especially  in  chil- 
dren, and  states  that  it  is  probably  the  most  com- 
mon cause  of  cystitis,  pyelitis  and  ascending  sup- 
purative nephritis.  In  fifty-eight  of  sixty  cases  of 
cystitis  in  children  the  colon  bacillus  was  found 
either  alone  or  in  mixed  cultures.  An  increased 
agglutinating  power  of  the  patient's  serum  for  the 
organisms  cultivated  from  the  urine  is  noted  in 
these  cases.  Davis  and  others  have  described  cases 
of  urinary  infections  due  to  B.  coli  differing  from 
the  usual  type  in  that  the  growth  on  various  media 
is  less  luxuriant  and  milk  is  not  coagulated. 

Davis  has  found  that  the  serum  of  patients  with 
such  infections  may  be  high  in  opsonic  power  and 
low  in  bacteriolytic,  or  vice  versa. 
Diarrheas.  Great  interest  attaches  to  the  colon  bacillus  in 
relation  to  enterocolitis  and  dysenteric  diseases. 
Escherich  speaks  of  an  enteritis  follicularis,  or 
colitis  contagiosa,  or  colicolitis,  epidemics  of  which 
have  been  noted  at  different  times.  A  number  of 
these  epidemics  occurred  before  the  identification 
of  the  dysentery  bacillus,  and  certain  of  them  may 
have  been  true  dysenteric  infections.  Neverthe- 
less, dysentery  bacilli  are  not  found  in  all  cases  of 
enterocolitis,    and    the    probability    that    genuine 


CHOLERA.  469 

cases  of  colon  enteritis  occur  can  not  as  yet  be  neg- 
lected. 

A  specific  colon  toxin  has  not  been  obtained. 

Immunization  with  the  colon  bacillus  causes  the 
formation  of  bactericidal  amboceptors,  opsonins 
and  agglutinins. 

Not  all  strains  of  the  colon  bacillus  are  identical   Aereiutina- 

I  ion. 

in  their  agglutinogenic  receptors.  A  serum  which 
agglutinates  one  colon  strain  does  not  necessarily 
agglutinate  all  strains.  The  reaction,  according  to 
Paltauf  and  others,  is  largely  an  individual  one. 
The  serum  of  a  patient  with  a  colon  infection  will 
agglutinate  the  strain  causing  the  disease,  but  may 
not  aifect  other  strains.  Hence,  for  diagnostic 
purposes,  the  test  must  be  performed  with  the  cul- 
ture which  has  been  obtained  from  the  patient. 
Pfaundler  says  in  reference  to  colicolitis  that  if 
other  colon  infections  can  be  excluded,  and  if  the 
serum  of  the  patient  gives  the  agglutination  reac- 
tion in  a  dilution  of  1  to  50  with  the  bacillus 
which  has  been  cultivated  from  the  stools,  colon 
infection  is  indicated  (Paltauf). 

Vaccine  therapy  has  been  successfully  applied  to  Th^r^^py 
many    of    these    colon    bacillus    infections.      The 
autogenous  organism  should  always  be  used  owing 
to  variation  in  the  bacilli,  especially  in  infections 
of  the  urinary  tract. 

VI.    CHOLERA. 

In  1883  Koch  discovered  the  Vibrio  cliolerce  and 
cultivated  it  from  the  stools  of  cholera  patients. 
The  organism  may  be  cultivated  from  the  stools  of 
the  patients  invariably,  and  is  never  found  in  other 
diseases  nor  in  normal  stools,  except  in  the  case  of 
non-susceptible  persons  who  may  be  encountered 


Cbaracteris- 
tics  of  tlie 


470  INFECTION     AND     IMMUNITY. 

during  an  epidemic.     The  latter  are  a  source  of 
danger  as  ^^cholera  carriers/' 

Typically  the  cholera  vibrio  is  about  1.5  microns 
orgranisnr.  loug  and  ouc-fourth  as  broad.  The  cells  of  young 
cultures  have  the  so-called  comma  shape  which  has 
given  the  organism  the  name  of  the  comma  bacil- 
lus. The  form  in  reality  is  that  of  a  segment  of  a 
spiral.  When  two  cells  are  attached  end  to  end  an 
S-shape  may  be  produced,  and  long  spirals  are 
made  up  of  many  cells  which  are  joined  at  the 
ends.  In  old  cultures  the  cells  may  assume  the 
form  of  thick  rods  or  even  appear  coccus-like.  The 
vibrio  possesses  a  single  long  fiagellum,  which  is  sit- 
uated at  the  end.  Although  two,  four  and  six  flag- 
ella  have  been  described,  KoUe  states  that  such  or- 
ganisms are  vibrios  of  another  nature.  In  the 
character  and  rapidity  of  their  movement,  as  seen 
in  a  hanging-drop,  Koch  compares  them  to  a 
swarm  of  mosquitoes.  Old  cultures  may  lose  their 
motility  to  a  large  extent.  The  cholera  vibrio 
does  not  form  spores,  although  certain  involution 
forms  simulate  them.  It  stains  readily  with  the 
ordinary  anilin  dyes  and  is  Gram  negative. 
Cultivation  The  comma  bacillus  grows  readily  in  alkaline 
stools,  culture  media  with  characteristic  appearances;  it 
is  an  obligate  aerobe  under  artificial  conditions,  in 
spite  of  the  fact  that  it  flourishes  in  the  intes- 
tines. The  optimum  temperature  lies  between  30° 
and  40°  C.  A  very  simple  method  of  obtaining  the 
organism  in  pure  culture  from  the  stools  was  dis- 
covered by  Koch.  In  tubes  of  peptone  bouillon 
which  have  been  inoculated  with  the  feces  of  a 
patient,  the  vibrio  proliferates  rapidly  and  within 
a  few  hours  exists  in  almost  pure  culture  at  the 
surface  of  the  liquid.     Isolated  colonies  are  ob- 


CHOLERA     VIBRIO.  471 

tained  by  transferring  a  small  amount  of  the  sur- 
face fluid  to  tubes  of  liquefied  gelatin,  then  plating 
the  latter.  The  colonies  appear  in  a  few  hours  as 
small  translucent  points  from  which  pure  cultures 
are  made  on  a  suitable  medium.  For  more  positive  idemifica- 
identification  agglutination  tests  are  performed  ****"• 
with  anticholera  serum.  The  Eoyal  Institute  for 
Infectious  Diseases  (Berlin)  keeps  on  hand  a  dried 
serum  of  known  strength  (1-10,000)  for  this  pur- 
pose. The  tests  being  made  with  high  dilutions, 
coagglutinins  for  other  vibrios  are  practically  elim- 
inated. To  the  agglutination  test  may  be  added 
the  "Pfeiffer  experiment,'^  in  which  the  protective 
power  of  an  anticholera  serum  is  determined  when 
guinea-pigs  are  infected  intraperitoneally  with  the 
suspected  culture.  If  the  serum  shows  a  protective 
power  against  this  organism  which  approximates 
that  shown  against  a  laiown  cholera  vibrio,  or,  if 
the  organisms  are  dissolved,  the  diagnosis  of  chol- 
era is  justified.  In  performing  such  experiments 
the  serum  is  mixed  with  the  culture  before  injec- 
tion. 

The  resistance  of  the  cholera  vibrio  is  very  low.  Resistance. 
It  dies  in  about  two  hours  when  dried  (Koch)  and 
on  this  account  dust  infection  is  thought  not  to 
occur.  It  is  killed  instantly  by  the  boiling  tem- 
perature, and  in  five  minutes  at  80°  C.  It  is  ex- 
tremely susceptible  to  carbolic  acid  (killed  by  1 
per  cent,  in  five  minutes),  corrosive  sublimate  (1 
to  2,000,000  or  3,000,000  in  from  five  to  ten  min- 
utes), and  to  acids.  Calcium  chlorid  is  an  effi- 
cient disinfectant  when  thoroughly  mixed  with  the 
stools.  The  micro-organism  lives  in  distilled  water 
not  longer  than  twenty-four  hours,  in  ordinary 
water  for  several  days  to  several  weeks,  and  in  one 


lion. 


472  INFECTION     AND     IMMUNITY. 

instance  it  was  cultivated  from  the  water  of  an 
aquarium  after  several  months.  Its  life  is  short  in 
the  prei-ence  of  putrefactive  bacteria  and  rapidly- 
growing  saprophytes,  dying  in  sewer  water  in  from 
twenty-four  to  thirty  hours  (Koch).  Because  of 
the  large  overgrowth  of  other  organisms,  the  vibrio 
can  rarely  be  cultivated  from  the  stools  later  than 
from  one  to  tliree  days  after  death.  Its  life  in  and 
on  foods  depends  on  the  reaction  (alkalinity  is 
favorable),  and  on  the  presence  or  absence  of 
moisture.  It  lives  longer  in  sterilized  milk  (ten 
days)  than  in  that  which  contains  other  micro-or- 
ganisms. 
Infection  InfcctioH  develops  in  the  small  intestines  fol- 
^Dissemina-  lowiug  ingestion  of  the  organisms.  Infection  by 
way  of  the  lungs  or  through  wounds  does  not  take 
place.  In  the  patient  the  living  vibrio  occurs  only 
in  the  intestines,  and  it  is  excreted  only  with  the 
feces.  So  far  as  known,  it  has  no  normal  habitat 
outside  the  body,  although  a  stream  or  other  water 
supply  may  contain  the  vibrio  over  a  long  period 
through  constant  reinfection  of  the  water.  This 
can  only  occur,  directly  or  indirectly,  through  the 
stools  of  patients.  The  washing  of  soiled  linen  or 
bathing  in  water  which  is  used  for  drinking  and 
other  household  purposes  have  caused  outbreaks  of 
cholera.  The  water  supply  of  a  city  may  be  in- 
fected by  the  discharges  of  patients  who  are  con- 
fined to  a  ship.  Convalescents  may  retain  virulent 
organisms  in  their  stools  for  forty-eight  days 
(Kolle),  and,  as  stated,  healthy  persons  who  are 
insusceptible  to  cholera  and  who  have  resided  in 
an  infected  district  may  carry  virulent  vibrios  in 
their  intestines.  These  conditions  have  contrib- 
uted to  the  futility  which,  to  a  large  degree,  has 


DISSEMINATION.  473 

met  attempts  to  limit  the  extension  of  cholera  by 
quarantine  measures.  Cholera  extends  from  coun- 
try to  country  along  the  lines  of  travel.  In  some 
instances  it  has  been  possible  to  trace  the  origin 
of  widespread  epidemics  to  the  delta  of  the  Ganges,  Epidemics. 
a  region  in  which  the  disease  is  endemic.  Pilgrims 
from  India  carry  the  infection  to  Mecca,  and  pil- 
grims from  Egypt  carry  it  to  their  native  land  on 
their  return  from  Mecca.  Either  from  Egypt,  or 
through  Arabia,  Asia  Minor  and  Southern  Russia 
or  Turkey,  cholera  has,  with  more  or  less  rapidity, 
extended  to  Western  Europe.  The  development  of 
rapid  transit  has  increased  the  rapidity  with  which 
cholera  may  extend.  From  Europe  the  disease  has 
been  carried  to  various  ports  of  the  western  conti- 
nent, Canada,  the  West  Indies  and  southern  ports 
of  the  United  States,  from  which  extension  has  oc- 
curred to  different  sections.  Of  six  widespread 
epidemics  of  the  past  one  hundred  years,  three 
have  involved  the  United  States,  reaching  consid- 
erable proportions.  The  means  of  introduction  is 
not  always  apparent. 

As  in  typhoid,  two  types  of  epidemics  are  known, 
the  two  often  being  associated:  First,  that  caused 
by  water  infection,  and,  second,  that  in  which  the 
disease  spreads  by  direct  and  indirect  contact.  The 
explosive  character  of  an  epidemic  caused  by  in- 
fection of  a  water  supply  is  much  more  striking 
than  in  the  case  of  typhoid  fever.  In  large  cities 
hundreds,  or  thousands,  may  be  striken  within  a 
day.  The  brief  incubation  period,  from  twelve  to 
twenty-four  hours,  contributes  to  the  acuteness  of 
the  outbreak.  The  distribution  of  a  "water- 
borne"  epidemic  corresponds  with  the  distribution 
of  the  infected  water.    A  remarkable  occurrence  il- 


474  INFECTION     AND     IMMUNITY. 

lustrating  this  point  was  noted  in  the  epidemic 
which  attacked  Hamburg  in  1892.  In  certain 
streets  in  which  the  residents  of  the  two  sides  ob- 
tained their  water  supply  from  different  sources, 
one  of  which  was  infected,  cholera  was  limited  to 
that  side  which  was  supplied  with  infected  water. 
Only  irregular  cases  due  to  contact  infection  oc- 
curred on  the  opposite  side  of  the  street. 

Epidemics  which  are  due  solely  to  contact  infec- 
tion develop  slowly  and  irregularly.  A  common 
incident  is  the  successive  involvement  of  the  mem- 
bers of  a  family,  whereas  others  in  the  immediate 
neighborhood  are  unaffected.  Water-borne  epi- 
demics are  invariably  complicated  by  the  occur- 
rence of  contact  infection.  The  methods  of  con- 
tact infection  are  not  different  from  those  men- 
tioned under  typhoid  fever.  Food  or  milk  which 
has  been  infected  by  contaminated  water  or  by 
other  means  may  cause  the  development  of  isolated 
groups  or  cases. 
suscepti-  Animals  do  not  contract  cholera  under  natural 
Animals,  conditious.  By  rendering  the  gastric  contents  of 
guinea-pigs  alkaline  and  introducing  cultures  into 
the  stomach  through  a  tube,  Koch  induced  a  chol- 
era-like process  from  which  the  animals  died  with- 
in from  twenty-four  to  thirty-six  hours;  an  intra- 
peritoneal injection  of  opium,  to  quiet  peristalsis, 
seemed  to  be  necessary  for  the  success  of  the  ex- 
periment. Similar  results  were  obtained  in  very 
young  rabbits  by  feeding  cultures  to  them  (Issaeff 
and  Kolle,  Metchnikoff).  Guinea-pigs  withstand 
the  subcutaneous  inoculation  of  moderate  amounts, 
but  are  verj  susceptible  to  intraperitoneal  inocula- 
tion. Intravenous  injections  are  exceedingly  toxic 
for  rabbits,  and  a  fatal  cholera-like  condition  with 


CHOLERA     ENDOTOXIN.  475 

localization  of  the  organisms  in  the  intestines  and 
intestinal  mucosa  has  been  produced  in  this  way 
(Thomas). 

The  essential  poison  of  the  cholera  vibrio  is  in-  Endotoxin. 
tracellular,  and  becomes  free  only  after  solution  of 
the  bacterial  cells.  Cultures  which  are  killed  care- 
fully as  by  chloroform  vapor  (Pfeiffer)  are  highly 
toxic,  although  the  fluid  alone  is  non-toxic.  The 
filtrates  of  young  cultures  have  little  or  no  poison- 
ous action.  The  toxicity  of  older  filtrates  is  due 
partly  to  the  solution  of  the  bacteria  with  conse- 
quent liberation  of  endotoxin,  and  perhaps  also  to 
secondary  disintegration  products  which  have  a 
certain  toxicity.  The  soluble  toxin  of  Metchni- 
koff,  Eoux,  and  Taurelli-Salimbeni  is  a  dissolved 
endotoxin  and  not  a  secretion  of  the  living  cells, 
according  to  Kolle. 

Koch  considers  that  cholera  is  an  acute  infec-    conditions 

in   the 

tious  process  of  the  intestinal  epithelium,  whereas  intestines. 
the  general  condition  is  one  of  acute  intoxication. 
It  is  assumed  that  the  condition  in  the  intestines 
corresponds  to  that  in  the  culture  media,  i.  e.,  that 
here,  too,  no  true  soluble  toxin,  comparable  with 
that  of  diphtheria  or  tetanus,  is  secreted,  but  that 
the  toxin  which  eventually  reaches  the  circulation 
is  that  which  is  liberated  from  the  bacteria  after 
the  latter  have  been  dissolved  by  the  bacteriolysin 
of  the  plasma,  or  perhaps  by  the  leucocytes.  Doubt- 
less a  great  deal  of  endotoxin  is  liberated  in  the  in- 
testinal canal,  but  it  is  Koch^s  conception  (cited 
by  Kolle)  that  the  primary  intoxication  comes 
from  those  organisms  which  have  penetrated  be- 
tween and  beneath  the  epithelial  cells  and  here 
have  undergone  solution.  One  effect  of  the  toxin 
in  this  situation  is  to  cause  desquamation  of  the 


470  INFECTION     AND     IMMUNITY. 

intestinal  epithelium,  as  a  consequence  of  which 
rapid  absorption  of  the  toxin  from  the  intestinal 
canal  takes  place  through  the  denuded  surface. 
This  theory  supposes  that  the  toxin  is  not  readily 
absorbed  through  the  intact  epithelium.  The  liv- 
ing vibrio  has  never  been  cultivated  from  the 
blood. 

The  changes  in  the  intestines  depend  on  the 
duration  of  the  infection.  In  cases  which  prove 
fatal  within  a  few  hours  the  mucosa  shows  only 
moderate  general  reddening,  which  is  intensified 
at  the  borders  of  Peyer's  patches  and  the  solitary 
follicles.  The  intestinal  contents  are  of  a  rather 
clear  fluid  nature  in  which  are  suspended  flakes  of 
mucus  and  epithelium;  the  fluid  may  be  tinged 
with  blood.  With  a  longer  duration  the  destructive 
processes  in  the  mucosa  become  more  intense,  and 
consist  largely  of  desquamation  of  the  superficial 
epithelium  and  intense  congestion  of  the  denuded 
submucosa.  In  the  more  prolonged  cases,  "chol- 
era-typhoid," the  mucosa,  especially  above  the  ileo- 
cecal valve,  may  show  diphtheritic  necrosis.  The 
serous  surface  of  the  intestines  is  injected. 
Prophylaxis.  The  rational  prophylaxis  founded  by  Koch,  on 
a  knowledge  of  the  biologic  characteristics  of  the 
comma  bacillus,  has  proved  of  great  efficiency. 
The  essential  points  are  the  following:  1.  Imme- 
diate bacteriologic  examination  of  the  stools  in 
suspicious  cases.  2.  Absolute  isolation  of  patients, 
in  a  hospital  whenever  possible.  3.  Thorough  dis- 
infection of  the  stools,  linen,  room  and  all  articles 
with  which  the  patient  has  been  in  contact,  includ- 
ing water-closets  and  privies.  4.  Continued  iso- 
lation during  convalescence  until  the  stools  are 
free  from  vibrios.     5.  Repeated  bacteriologic  ex- 


riiOPHYLAXIS.  477 

animation  of  the  stools  of  those  who  have  been  in 
contact  with  cholera  patients  until  their  freedom 
from  vibrios  is  assured.  6.  Frequent  examination 
of  the  water  supply  at  different  points  in  order  to 
detect  the  occurrence  of  water  infection.  7.  In 
case  water  infection  exists,  exclusion  of  the  water 
from  all  domestic  uses,  and  the  institution  of 
means  to  rid  the  water  of  infection.  This  may  be 
done  in  the  case  of  infected  wells,  but  in  the  case 
of  large  systems  reconstruction  may  be  necessary 
for  future  protection.  Water  for  household  use 
should  be  boiled.  Kolle  compares  the  conditions 
•  in  Germany  and  Eussia  during  the  epidemic  of 
1892-4.  In  Germany,  where  Koch^s  principles  of 
prophylaxis  were  rigidly  observed,  about  10,000 
cases  occurred,  9,000  of  which  were  confined  to 
Hamburg,  whereas  in  Eussia,  where  precautions 
were  not  enforced  strictly  or  generally,  800,000 
cases  developed  during  the  same  period. 

Protective  inoculation  has  shown  itself  to  be  of  vaccination. 
distinct  value  for  prophylaxis.  Ferran,  a  Span- 
iard, first  practiced  vaccination  on  a  large  scale  in 
1884,  although  little  definite  knowledge  of  the 
value  of  the  procedure  resulted  from  his  work. 
He  is  supposed  to  have  used  impure  cultures.  Haff- 
kine  introduced  protective  inoculation  on  a  large 
scale  in  India,  and  up  to  1895  had  inoculated  40,- 
000  persons.  Following  Pasteur's  method  with 
anthrax,  he  used  two  vaccines.  Vaccine  1  was  a 
culture  which  had  been  attenuated  by  prolonged 
growth  at  39°  C.  Vaccine  2,  which  was  adminis- 
tered five  days  later,  was  a  virulent  culture.  The 
living  organisms  were  used  in  both  vaccines  and 
the  injections  were  given  subcutaneously.  The 
local  and  general  symptoms  were  mild.     Instead 


478  INFECTION     AND     IMMUNITY. 

of  living  cultures  Kolle  has  proposed  the  use  of 
virulent  cultures  which  have  been  killed  by  expo- 
sure to  a  temperature  of  58°  C.  for  one  hour.  The 
vaccine  is  preserved  by  the  addition  of  0.5  per 
cent,  phenol.  In  the  Japanese  epidemic  of  1902 
this  method  was  used  on  an  extensive  scale.  The 
incidence  of  disease  among  the  uninoculated  was 
13  per  cent.,  among  the  inoculated  0.06  per  cent. ; 
the  mortality  among  the  uninoculated  was  10  per 
cent.,  among  the  inoculated  only  0.02  per  cent. 
The  disease,  when  it  occurred  in  the  inoculated, 
was  of  a  mild  type.  A  single  injection  of  from  2 
to  4  mg.  of  a  killed  agar  growth  was  given  sub- 
cutaneously  (cited  by  Kolle).  Strong  has  pro- 
posed the  use  of  the  products  of  autolysis  of  the 
cholera  vibrio  as  a  vaccinating  substance,  a  method 
founded  on  the  observations  of  Neisser  and  Shiga 
in  relation  to  typhoid,  and  of  Conradi  and  Drigal- 
ski  in  relation  to  dysentery.  The  local  and  general 
symptoms  are  said  to  be  of  a  mild  type.  The 
method  has  had  no  practical  trial. 
Natnrai  From  what  was  said  above  in  connection  with 
anti"sliscep-  the  so-callcd  cholera  carriers,  it  is  evident  that  not 
all  are  equally  susceptible  to  infection  with  chol- 
era. In  the  few  instances  in  which  infection  has 
been  attempted  deliberately,  some  contracted  the 
disease,  at  least  one  case  ending  fatally,  whereas  in 
others  either  a  mild  infection  or  none  at  all  took 
place.  The  conditions  on  which  such  cases  of  in- 
dividual immunity  depend  are  not  known  conclu- 
sively, although  it  is  often  intimated  in  a  general 
way  that  a  strong  bactericidal  power  of  the  body 
fluids,  or  a  high  phagocytic  power  on  the  part  of 
leucocytes,  is  responsible  for  it.  The  gastric  juice, 
on  account  of  its  acidity,  offers  a  barrier  to  the 


tibility. 


IMMUNITY     IN     CHOLERA.  479 

passage  of  living  vibrios  into  the  small  intes- 
tines, and  this  is  particularly  true  of  cholera. 
It  is  nevertheless  evident  that  the  barrier  in  many 
instances  is  not  a  serious  one.  A  number  of  cases 
are  recorded  in  which  investigators  while  working 
with  cultures  have  become  infected  with  cholera, 
the  cases  running  typical  courses  which  sometimes 
ended  fatally  (Pfeiffer,  Pfuhl  and  others).  Or- 
ganisms which  are  ingested  with  water  may  pass 
rapidly  to  the  intestines  without  being  affected  by 
the  acid  of  the  stomach,  or  when  taken  with  food 
they  may  be  buried  in  the  latter  and  hence  not 
come  in  contact  with  the  gastric  secretion.  It 
seems  probable  that  the  intestinal  epithelium  has 
a  certain  resistance  to  invasion  which  is  most  mani- 
fest in  the  case  of  those  who  do  not  become  in- 
fected in  spite  of  the  presence  of  the  organisms  in 
their  intestines.  Natural  immunity  appears  to  be 
one  which  is  directed  against  the  bacteria  rather 
than  against  the  endotoxin,  proliferation  of  the 
organisms  in  the  intestinal  epithelium  being  pre- 
vented. Poorly  nourished  individuals,  the  very 
young  and  the  very  old  are  particularly  suscepti- 
ble. Other  gastrointestinal  disorders,  in  the  pres- 
ence of  an  epidemic,  predispose  to  infection.  De- 
fects in  the  intestinal  epithelium,  or  a  decreased 
resistance  of  the  latter,  may  afford  favorable 
ionditions  for  invasion. 

Active  immunity,  as  that  which  results  from  in-  Ac«iuire«i 
fection  or  from  protective  inoculation,  is  charac- 
terized by  the  appearance  of  bactericidal  ambocep- 
tors, opsonins,  agglutinins  and  specific  precipitins 
in  the  serum. 

Amako    finds    that    opsonin,    bactericidin    and 
agglutinin  develop  with  the  course  of  the  disease. 


Iininiinity, 


480  INFECTION     AND     IMMUNITY. 

The  length  of  the  negative  phase  varies  with  the 
severity  of  the  sj^mptoms.  The  fulminating  cases 
have  a  short  negative  phase  ending  in  death.  The 
antibodies  reach  their  height  during  convalescence, 
the  bacteriolysins  iisnallv  developing  most  rapidly. 
In  most  cases  the  three  antibody  curves  run 
parallel,  but  the  bacteriolysins  may  be  much  more 
highly  developed  than  the  opsonins. 

According  to  Pfeiffer  and  Marx,  the  antibodies 
are  produced  in  the  blood-formijig  organs.  An 
attack  of  cholera  confers  immunity  of  prolonged 
duration,  although  it  is  not  always  absolute. 

Passive  immunity  is  readily  induced  in  animals 
by  injection  of  anticholera  scrum.  As  in  other 
instances,  it  is  of  short  duration.  Doubtless  the 
same  condition  may  be  induced  in  man.  Besredka 
has  proposed  mixed  immunization  for  protective 
inoculation,  using  killed  bacteria  which  have  been 
saturated  with  the  specific  amboceptors. 
.Serotherapy       Serotherapy    has    been    no    more    successful    in 

una  Ag'Srlnti-  . 

nation,  cliolcra  than  in  typhoid  fever.  The  antitoxic 
serum  of  Eoux  and  others  has  had  no  practical 
trial.  According  to  Achard  and  Bensaude,  the 
serum  of  cholera  patients,  on  the  third  or  fourth 
day  of  the  disease,  agglutinates  the  cholera  vibrio. 
However,  they  used  the  serum  in  dilutions  of  1-20. 
and  in  this  strength  even  normal  human  serum 
may  be  agglutinating  (Pfeiffer  and  Kolle,  cited  by 
Paltauf).  Convalescents  even  after  seven  months 
may  show  an  agglutinating  power  of  from  1/100  to 
1/120. 

The  bacteriologic  examination  of  the  stools  is 
the  most  reliable  means  of  early  diagnosis  (see 
above). 


BACILLUS     PESTIS.  481 

VII.    PLAGUE. 

Plague  was  known  in  the  second  and  third  cen- 
turies. In  the  sixth  century  it  ravaged  the  Eoman 
empire  and  destroyed  half  the  population  in  the 
eastern  provinces.  Under  the  name  of  the  "black 
death"  it  swept  over  Europe  in  1347-50  with  a 
sacrifice  of  one-fourth  of  the  inhabitants — about 
25^000,000.  During  the  fifteenth  and  sixteenth 
centuries  many  epidemics  prevailed  in  various 
parts  of  Europe,  and  the  disease  seemed  to  have 
fastened  itself  on  that  part  of  the  world.  However, 
the  pneumonic  form  of  the  disease,  the  most  con- 
tagious, gradually  became  less  common,  or  the  vir- 
ulence of  the  infection  diminished,  and  this,  with 
the  institution  of  quarantine  regulations,  decreased 
the  prevalence  of  the  plague  during  and  following 
the  seventeenth  century.  Nevertheless,  there  have 
been  occasional  outbreaks  in  Eastern  Europe  since 
that  time.  Following  the  recrudescence  of  plague 
in  Hongkong  in  1893  and  in  other  places  later, 
the  disease  has  been  subjected  to  scientific  study, 
its  cause  has  been  discovered,  and  the  importance 
of  rigid  quarantine  measures  at  seaports  in  pre- 
venting its  universal  extension  has  been  proved. 

In  the  Hongkong  epidemic  of  1893-4  Kitasato  ciiaracteris- 
and  Yersin,  working  independently,  discovered  the  orgranism. 
bacillus  of  plague.  Bacillus  pestis.  The  organism  is 
minute  (1.5  to  1.75  by  0.5  to  0.7  microns),  and 
typically  is  of  long  oval  shape.  The  frequent  oc- 
currence of  short  oval  cells  (coccus  form),  longer 
rods  and  distorted,  swollen,  vacuoie-like  cells  (in- 
volution or  degeneration  forms)  signifies  a  high 
degree  of  pleomorphism  which  is  characteristic. 
The  longer  the  disease  has  lasted,  or,  on  the  other 
hand,  the  older  the  culture,  the  more  numerous  are 


482  INFECTION     AND     IMMUNITY. 

the  atypical  forms.  In  bouillon  long  chains  de- 
velop. It  is  non-motilCj  has  no  flagella  and  forms 
no  spores.  A  capsule  may  be  demonstrated  by  ap- 
propriate technic.  It  does  not  stain  by  Gram's 
method,  and  with  methylene  blue,  carbol  fuchsin, 
etc.,  the  ends  stain  more  densely  than  the  central 
portion  (polar  staining).  Because  of  its  general 
properties  it  is  placed  in  a  group  with  a  number  of 
bacteria  which  cause  hemorrhagic  septicemias  in 
various  animals — the  "hemorrhagic  septicemia 
group." 

There  occurs  in  bouillon  the  so-called  stalactite 
growth,  in  which  visible  processes  extend  from  the 
surface  toward  the  bottom,  where  they  meet  other 
processes  which  extend  toward  the  surface  "stalag- 
mites"). These  formations  utilize  as  their  starting 
points  the  side  of  the  flask  or  drops  of  butter  or 
oil  which  are  placed  on  the  surface.  Certain  other 
organisms  grow  in  a  similar  manner.  It  is  said 
to  be  a  characteristic  feature  of  the  plague  bacilli 
that  many  involution  forms  appear  on  agar  which 
contains  3  per  cent,  of  sodium  chlorid.  The  opti- 
mum temperature  for  growth  is  from  25°  to  30° 
C,  which  is  somewhat  lower  than  that  for  most 
pathogenic  organisms.  It  grows  rather  slowly  even 
under  the  best  conditions.  In  mixed  cultures  it  is 
overgrown  by  saprophytic  organisms  (e.  g.,  colon 
bacillus). 
Viability  The  plaguc  bacillus  may  live  for  from  four  to 
ReeiiHtance.  scvcu  days  in  the  putrefying  organs  of  man  or  ani- 
mals. Its  virulence  may  be  retained  in  the  cadaver 
of  a  rat  for  two  months  (Bandi  and  Stagnitta- 
Balistreri).  During  this  time  the  organisms  pene- 
trate all  the  tissues  of  the  body,  even  growing 
through  the  skin.     It  may  live  in  the  pus  of  a 


BACILLUS     PESTIS.  483 

bubo  for  tAveiity  days  when  unmixed  with  other 
organisms  (Albrecht  and  Ghon)  ;  in  the  sputum 
from  plague  pneumonia  for  ten  days;  in  various 
foods,  as  milk,  potatoes,  for  one  to  three  weeks ;  in 
water  from  five  to  twenty  days,  depending  on  the 
number  of  saprophytes  which  are  present;  in  earth 
from  two  weeks  to  three  months,  depending  on  the 
quantity  of  organic  matter  and  other  organisms. 
In  all  these  instances  the  higher  the  temperature, 
i.  e.,  above  30°  C,  and  the  more  numerous  the 
saprophytic  organisms,  the  shorter  is  the  life  of 
the  plague  bacillus.  In  winter,  when  contaminat- 
ing saprophytes  grow  less  rapidly,  the  plague  bacil- 
lus lives  longer.  Its  resistance  to  desiccation,  sun- 
light and  disinfecting  agents  is  rather  low,  par- 
ticularly when  the  surrounding  temperature  is 
above  30°  C.  In  temperatures  of  from  29°  to  31° 
C,  when  thorouhgly  dried,  it  rarely  lives  longer 
than  from  six  to  seven  days,  whereas  at  lower  tem- 
peratures, 16°  to  20°  C,  cultures  may  be  obtained 
after  from  one  to  several  weeks,  depending  on  the 
material  which  contains  the  organisms.  It  lives 
longer  in  woolen  and  cotton  threads  (clothing) 
than  when  isolated  as  in  dust ;  hence,  dust  infection 
is  improbable  (Dieudonne).  In  sputum  (plague 
pneumonia)  and  purulent  exudates  in  which  the 
bacilli  become  incrusted  to  a  degree,  life  may  per- 
sist for  from  three  to  four  weeks.  Sunlight  kills 
them  in  from  two  to  six  hours,  depending  on  the 
temperature  and  the  proximity  of  the  organisms  to 
the  surface.  Although  cultures  for  the  purpose  of 
vaccination  have  been  killed  at  a  temperature  of 
65°  C.  for  one  hour,  precautions  to  insure  an  even 
distribution  of  the  heat  are  necessary  to  render  cer- 
tain the  death  of  all  organisms.  A  temperature  of 


484 


INFECTION     AND     IMMUNITY. 


Virulence 
and  Toxins. 


Virulence 
for  AninialM. 


100°  C.  kills  them  at  once,  and  80°  C.  in  from  five 
to  ten  minutes  (moist  heat).  They  are  very  resis- 
tant to  cold,  remaining  alive  at  a  temperature  of 
— 20°  C.  for  several  weeks,  even  when  repeatedly 
thawed  out  during  this  time,  and  they  even  prolif- 
erate slowly  at  from  4°  to  7°  C. 

Cultures  of  the  plague  bacillus  retain  their  viru- 
lence over  a  long  period  when  kept  in  a  cool  dark 
place  and  when  not  allowed  to  dry.  However, 
they  often  loose  in  virulence  unaccountably.  The 
nature  of  the  toxic  substance  is  as  yet  obscure.  A 
concentrated  soluble  toxin  has  never  been  obtained 
in  cultures.  Filtrates  of  young  cultures  show  lit- 
tle or  no  toxicity,  whereas  in  older  cultures  the 
fluid  becomes  more  or  less  toxic  (liberation  of  en- 
dotoxin?). Lustig  and  Cxaleotti  extract  cultures 
with  0.75  to  1  per  cent,  potassium  hydroxid,  from 
which  they  precipitate  a  toxic  substance  with  ace- 
tic or  hydrochloric  acid.  Markl  found  the  cell 
bodies  to  be  very  toxic  after  eight  weeks'  growth  at 
room  temperature,  provided  the  organisms  were 
killed  by  chloroform  rather  than  by  heat;  killing 
by  heat  destroys  the  toxic  substance  largely.  He 
believes  some  metabolic  product  of  the  organism 
is  the  chief  toxic  constituent,  claiming  at  the  same 
time  the  presence  of  a  certain  amount  of  soluble 
toxin. 

The  plague  bacillus  is  exceedingly  virulent  for 
rats,  squirrels,  guinea-pigs  and  monkeys ;  somewhat 
less  virulent  for  mice  and  adult  rabbits ;  other  ani- 
mals, cats,  dogs,  swine,  cows,  horses,  sheep,  goats, 
may  be  infected  artificially,  although  they  com- 
monly recover  even  after  large  doses.  Guinea-pigs 
and  rats  may  be  infected  by  subcutaneous,  intraperi- 
toneal and  intravascular  injections,  by  the  feeding 


TRANSMISSION     TO     ANIMALS.  485 

of  infected  material  or  by  placing  it  on  the  nasal 
mucous  membrane  or  in  the  conjunctival  sac.  and  by 
inhalation  experiments,  the  last  method  commonly 
resulting  in  plague  pneumonia.  Guinea-pigs  and 
young  rabbits  die  of  plague  septicemia  in  from 
four  to  five  days  when  cultures  or  material  con- 
taining the  organisms  (sputum,  feces,  organs  from 
plague  cases),  are  rubbed  into  the  shaven  or  even 
unshaven  skin  (Albrecht  and  Ghon).  This  experi- 
ment is  of  value  for  detecting  virulent  plague  ba- 
cilli and  separating  them  from  contaminating  or- 
ganisms. Following  inoculation  into  a  cutaneous 
or  mucous  surface  a  local  reaction  of  varying  in- 
tensity develops  in  which  the  subcutaneous  tissue 
becomes  edematous  or  even  hemorrhagic,  in  a  num- 
ber of  hours  the  regional  lymph  glands  become 
swollen  and  hemorrhagic,  and  in  from  two  to  five 
days  the  animals  die  of  plague  septicemia.  Cul- 
tures of  low  virulence  not  infrequently  cause  a 
chronic  infection  which  is  characterized  by  the  for- 
mation of  large  granulomatous  nodules  on  the  sur- 
face of  the  liver  and  spleen  and  in  the  omentum. 
Such  foci  contain  many  plague  bacilli,  and  the 
death  of  the  animal  results  in  a  few  weeks  from 
intoxication  or  from  general  infection.  Although 
rabbits  are  much  less  susceptible  than  rats  or 
guinea-pigs,  5'oung  animals  succumb  to  cutaneous 
inoculation. 

Dieudonne  cites  four  foci  in  which  plague  is  Endemic 
known  to  be  endemic  at  the  present  time :  One  is  ^*^^^®* 
in  China  (province  of  Yiinnan),  from  which  the 
Hongkong  epidemic  originated;  a  second  in  the 
Himalayas,  which  led  to  the  outbreak  in  Bombay; 
a  third  in  a  mountainous  region  south  of  Mecca, 
and  a  fourth  was  found  by  Koch  and  Zupitza  in 


4SG  INFECTION     AND     IMMUNITY. 

British  East  Africa  near  the  source  of  the  White 
Nile. 
Plague  The  opinion  is  held  by  many  that  plague  is  pri- 
*"  s^u*  rrei^  mai'ily  a  disease  of  the  rat  and  that  certain  regions 
remain  pest-infected  because  of  this  fact.  Eats,  in 
certain  districts,  suffer  from  a  chronic  form  of  the 
disease,  and  it  is  possible  that  the  organism  at 
times  acquires  increased  virulence,  as  a  conse- 
quence of  which  the  infection  becomes  widespread 
and  rapidly  fatal  among  these  animals.  It  is 
believed  that  transmission  from  rat  to  rat  may 
occur  through  the  eating  of  plague  cadavers. 
Experiments  are  also  reported  showing  that  fleas 
from  plague-stricken  rats  will  infect  healthy  rats, 
guinea-pigs  and  monkeys  by  biting  them.  The 
work  of  the  Indian  Plague  Commission  demon- 
strated that  the  usual  means  of  transmission  from 
rat  to  rat  and  from  rat  to  man  is  by  means  of 
fleas.  Monkeys,  which  are  readily  infected  if  put 
in  the  same  room  with  infected  rats,  remain  well 
if  protected  from  fleas.  It  has  been  repeatedly 
demonstrated  that  fleas  from  rats  and  squirrels 
will  feed  on  man. 

In  California,  squirrels  infected  with  plague  are 
an  important  source  of  infection  in  man.  Trans- 
mission from  rats  to  squirrels  and  from  squirrels 
to  rats  by  means  of  fleas  has  been  demonstrated  by 
McCoy,  and  McCoy  and  AYherry  report  a  case  of 
transmission  from  squirrels  to  man.  probably 
through  fleas. 

Flies,  as  well  as  fleas,  may  rlistribute  the  bacilli 
from  rats  or  the  infected  oxcretious  of  man 
mechanically. 

When  plague  invades  a  new  country  it  commonly 
makes   its   first  appearance   in   coast  cities.     Pre- 


TRANSMISSION     OF     PLAGUE.  487 

sumably  this  is  accomplished  through  infected  rats 
which  may  board  a  ship  during  its  stay  in  a  pest- 
ridden  harbor,  and  which  subsequently  escape  at 
the  new  port. 

Epidemics  of  plague  lack  the  explosive-like  sud-  Epidemic*. 
denness  in  their  development  which  characterizes 
cholera  and,  to  a  certain  extent,  typhoid  and  dys- 
entery. The  cases  occur  in  groups  and  in  particu- 
lar houses  in  such  a  manner  that  direct  and  indi- 
rect contact  seem  to  be  largely  responsible  for 
transmission.  Every  epidemic  of  plague  may  be 
divided  into  three  stages:  a  slow  progression  from 
small  centers,  an  acme  of  widespread  death,  and  a 
slow  recession  (Dieudonne).  It  seems  probable 
that  the  disease  spreads  rapidly  and  extensively 
only  when  the  pneumonic  form  prevails. 

In  man  infection  takes  place  through  the  skin  ^'^2!***" 
most  frequently,  although  the  mucous  membranes 
of  the  mouth,  nose,  pharynx,  tonsils  or  the  con- 
junctiva are  possible  infection  atria.  Often  no 
local  reaction  is  produced,  and  the  point  of  en- 
trance may  be  indicated  only  in  a  general  way  by 
the  swollen  lymph  glands  of  the  region.  Infre- 
quently a  pustule  or  small  carbuncle  marks  the 
point  of  entrance.  Primary  plague  pneumonia  is 
caused  by  the  inhalation  of  pest-laden  material, 
particularly  fine  particles  of  sputum  from  a  pneu- 
monic case,  and  perhaps  also  by  the  inhalation  of 
infected  dust;  the  latter  is  probably  of  less  impor- 
tance because  of  the  short  life  of  the  organism  in 
dust.  Even  in  ordinary  speaking  minute  drops  of 
saliva  are  thrown  into  the  air.  Infection  is  thought 
not  to  occur  through  the  stomach  or  intestines. 
In  the  pneumonic  and  septicemic  forms,  the  in- 
fected urine  and  feces  contribute  to  the  dissemina- 


488  INFECTION     AND     IMMUNITY. 

tion  of  the  organisms.  Compared  with  pneumonic 
and  septicemic  plague  the  bubonic  form  is  much 
less  dangerous  to  a  community. 

Following  cutaneous  infection  the  regional 
lymph  glands  become  swollen  and  hemorrhagic, 
and  undergo  more  or  less  extensive  necrosis.  When 
the  infection  extends  beyond  the  lymph  glands  the 
blood  may  contain  enormous  quantities  of  bacilli 
(plague  septicemia),  and  the  same  condition  fol- 
low^s  plague  pneumonia ;  in  the  event  of  general  in- 
fection death  follows  in  a  few  hours.  "Secondary 
pneumonia"  and  also  "secondary  buboes'^  develop 
as  a  consequence  of  blood  infection.  Hemorrhages 
into  the  mucous  membrane  (especially  the  stom- 
ach or  cecum),  endothelial  surfaces  (pericardium), 
and  various  parenchymatous  organs,  with  extreme 
degeneration  of  the  latter  (liver,  kidneys  and 
heart),  are  characteristic  anatomic  changes.  The 
spleen  is  usually  swollen.  The  toxic  substance 
evidently  has  affinities  for  many  tissues. 

Mixed  infection  with  the  streptococcus  is  not 
uncommon  and  is  a  serious  complication. 
Prophylaxis.  The  following  are  important  points  for  prophy- 
laxis: 1.  Early  diagnosis  as  established  by  bac- 
teriologic  examination  of  blood,  sputum,  and  fluid 
taken  from  a  bubo  either  by  a  syringe  or  after  in- 
cision; 2,  in  the  thorough  isolation  of  patients  and 
of  those  who  have  been  exposed  to  infection;  3, 
in  the  disinfection  of  excretions,  of  clothing  and  of 
infected  houses,  which  in  some  instances  may 
mean  the  destruction  of  the  latter;  4,  in  the  de- 
struction of  rats;  5,  prophylactic  injections.  Up 
to  the  present  time  the  most  effective  measure  of 
getting  rid  of  rats  is  to  offer  a  bounty  for  each 
animal  caught,  as  practiced  in  Manila.     Tn  Cali- 


PROPHYLAXIS.  489 

fornia,  the  work  of  extermination  of  squirrels,  rats 
and  fleas  lias  been  carried  on  extensively  by  the 
U.  S.  Public  Health  and  Marine-Hospital  Service. 

The  vaccine  of  Haffldne  has  been  used  exten-  vaccines. 
sively  in  India.  The  Indian  plague  commission 
found  that  the  incidence  of  disease  and  the  mor- 
tality were  lower  among  the  inoculated  than  the 
uninoculated,  although  many  of  the  inoculated 
contracted  the  disease  in  a  benign  form.  The  vac- 
cine consists  of  bouillon  cultures  which  have  grown 
for  six  weeks  with  stalactite  formation  (see  above), 
then  killed  by  exposure  to  a  temperature  of  65°  C. 
for  one  hour;  from  0.5  to  3.5  c.c.  are  injected,  ac- 
cording to  the  age  and  size  of  the  individual.  One 
or  more  subsequent  injections  may  be  given.  The 
local  and  general  reactions  are  of  moderate  sever- 
ity. Protection  becomes  manifest  only  several 
days  after  the  inoculation  and  may  persist  for 
many  weeks  or  months.  The  vaccine  recommended 
by  the  German  commission  consists  of  two  days* 
old  agar  cultures  which  have  been  killed  by  heat 
(65°  C.  for  one  hour).  Lustig  and  Galeotti  utilize 
the  toxic  precipitate  described  above  as  a  vaccine. 
Terni  and  Bandi  inoculate  rabbits  or  guinea-pigs 
intraperitoneally  with  the  plague  bacillus  and 
after  or  just  preceding  death  collect  the  peritoneal 
exudate,  in  which  the  organisms  are  allowed  to  pro- 
liferate still  further  for  twelve  hours.  The  bacilli 
are  then  killed  at  a  low  temperature,  and  this 
fluid,  after  an  addition  of  a  preservative,  consti- 
tutes their  vaccine.  Although  the  last  three  vac- 
cines have  proved  of  value  in  animal  experiments, 
they  have  not  as  yet  been  used  extensively  in  man. 

Besredka  and  Shiga  recommend  the  use  of  mixed 
active  and  passive  immunization,  as  suggested  in 


490  INFECTION     AND     IMMUNITY. 

relation  to  typhoid  and  cholera,  in  this  instance 
natural^  using  plague  bacilli  (killed)  and  anti- 
plague  serum.  Shiga  reported  good  results  by  the 
use  of  the  combined  method  in  the  epidemic  in 
Kobe. 

The  immunity  which  is  produced  by  protective 
inoculation,  like  that  which  follows  natural  infec- 
tion, is  considered  to  be  antibacterial  inasmuch  as 
the  serum  acquires  increased  bactericidal  power  for 
the  bacillus,  but  shows  no  ability  to  neutralize  its 
toxic  constituents.  The  influence  of  opsonins  is 
essential  for  experimental  phagocytosis,  and  is  an 
important  factor  in  the  mechanism  of  immunity. 
Antiplague  serum  contains  also  complement-devi- 
ation antibodies  and  precipitins.  The  immunity 
which  follows  infection  is  of  long  duration. 
Serotherapy  Prophylactic  injections  of  antiplague  serum  pro- 
duce a  temporary  immunity  of  about  two  weeks' 
duration.  The  Pasteur  Institute  prepares  the 
serum  of  Yersin  by  immunizing  horses  first  with 
killed  and  then  with  living  cultures.  The  immun- 
ization is  difficult  and  from  several  months  to  a 
year  and  a  half  are  required  for  the  production  of 
a  strong  serum.  When  the  blood  is  drawn  its  free- 
dom from  living  plague  bacilli  and  from  toxic  sub- 
stances must  be  assured.  The  immunizing  value  of 
the  serum  is  determined  by  that  quantity  which 
will  save  a  mouse  from  a  fatal  dose  of  living  plague 
bacilli,  the  serum  being  given  24  hours  in  advance 
of  the  culture.  This  is  accomplished  by  0.1  to  0.02 
c.c,  depending  on  the  strength  of  the  serum.  Its 
curative  power  is  estimated  from  that  quantity,  0.5 
to  0.1  c.c,  which  saves  a  mouse  when  administered 
16  hours  after  the  injection  of  an  otherwise  fatal 
dose  of  culture.   For  protective  inoculation  in  man 


And   Propliy- 
laxis 


SEROTHERAPY.  4IJ1 

from  10  to  20  c.c.  are  recommended,  and  for  cura- 
tive purposes  from  30  to  50  c.c.  Concerning  the 
value  of  this  serum  Dieudonne  concludes  as  fol- 
lows: "On  the  basis  of  the  results  obtained  in 
man  and  in  animal  experiments  we  can  attribute 
no  positive  curative  value  to  the  Parisian  serum, 
although  a  certain  influence  on  the  course  of  the 
disease  can  not  be  denied.  On  the  other  hand,  the 
serum  is  suitable  for  protective  inoculation  when 
immediate  immunity  is  necessary,  as  for  those  who 
are  caring  for  cases  of  plague  pneumonia.  Since, 
however,  the  protection  afforded  by  this  means  per- 
sists only  for  a  few  days,  subsequent  active  immun- 
ization with  killed  cultures  is  indicated  as  soon  as 
possible  for  those  persons  who  are  exposed  to  in- 
fection for  some  time."  The  favorable  results 
noted  by  a  number  of  observers  would  seem  to  jus- 
tify further  use  of  the  serum  for  curative  pur- 
poses. 

The  serum  of  Tavel,  prepared  at  the  Institute 
of  Bern,  is,  like  that  of  Yersin,  bactericidal  and 
agglutinating.  Antitoxic  as  well  as  bactericidal 
properties  are  claimed  for  the  serum  of  Lustig, 
which  is  prepared  by  immunization  with  the  toxic 
precipitate  mentioned  above.  It  has  been  used  ex- 
tensively in  the  treatment  of  plague  and  in  a  num- 
ber of  small  epidemics  favorable  though  not  thor- 
oughly convincing  results  were  reported.  The 
serum  of  Markl,  which  is  supposed  to  be  antitoxic, 
has  had  no  practical  trial.  It  is  prepared  by  im- 
munization with  old  cultures  which  have  been 
killed  by  chloroform. 

According  to  Kolle  and  Krumbein  antiplague 
serum  should  be  tested  as  to  concentration  of  all  of 


492  lyFEGTION     AND     IMMUNITY. 

the  various  antibodies  in  order  to  obtain  a  correct 
idea  of  its  value. 
Agrgiuti-  Althonsrh  the  serum  of  patients  acquires  a  cer- 
tain  agglutinating  power,  it  is  rather  low  (1/3  or 
1/5),  and  does  not  become  manifest  until  during 
the  second  week  of  the  disease.  Before  this  time 
diagnosis  by  clinical  or  bacteriologic  means  can  be 
made  with  certainty;  hence,  for  clinical  diagnosis 
the  reaction  has  little  value.  On  the  other  hand, 
a  strong  artificial  agglutinating  serum  obtained 
by  the  specific  immunization  of  animals  is  of  great 
value  for  the  identification  of  the  plague  bacillus 
when  cultures  have  been  obtained  from  suspected 
cases.  Artificial  serums  may  agglutinate  in  dilu- 
tions of  from  1/1000  to  1/6000. 

B.  Diseases  in  which  acquired  immunity  is  not 
due  to  increased  bactericidal  power  of  the  serum,  or 
liuowledge  on  this  point  is  deficient. 

I.    ANTHRAX. 

From  the  standpoint  of  infection  and  immunity 
anthrax  is  of  particular  interest.  It  is  the  first 
disease  of  which  the  bacterial  etiology  was  proved 
and  in  which  the  specific  microbe  was  used  in  pure 
culture  for  the  production  of  artificial  immunity 
(vaccination). 

Anthrax  is  particularly  a  disease  of  cattle  and 
sheep,  and  it  prevails  in  certain  European  coun- 
tries, especially  Russia,  in  Australia  and  in  South 
America.  It  does  not  occur  extensively  in  this 
country.  Definite  regions  are  at  times  heavily  in- 
fected, and  it  is  in  such  localities  that  the  disease 
is  most  frequently  transmitted  to  man. 


AXTNh'AX.  493 

As  early  as  1850  Rayer  and  Devaine,  also  Pol-  Bacillus^ 
lender,  had  discovered  the  presence  of  small  rods 
and  filaments  in  the  blood  of  animals  which  had 
died  of  anthrax,  and  the  work  of  Koch,  Pasteur 
and  others  soon  established  that  this  rod,  the  an- 
thrax bacillus,  is  the  cause  of  anthrax.  The  discov- 
ery of  Koch  that  the  bacillus  forms  extremely  re- 
sistant spores,  explained  the  persistence  with  which 
the  disease  infects  particular  localities. 

The  anthrax  bacillus  is  a  fairly  large  organism,  sporea. 
is  rod-shaped,  non-motile  and  grows  with  charac- 
teristic appearances  on  various  culture  media. 
With  the  proper  temperature  and  culture  medium, 
and  in  the  presence  of  free  oxygen,  the  formation 
of  spores  begins  after  about  twenty-four  hours  of 
growth.  Their  evolution  is  complete  in  from  one 
to  two  days,  and  eventually  the  protoplasm  of  the 
cells  disintegrates  and  the  spores  are  set  free. 
Spores  are  not  formed  in  the  body  of  an  infected 
animal.  Spore  formation  is  not  essential,  how- 
ever, for  the  continued  life  of  the  organism;  at 
high  temperatures  (42°  C),  and  in  the  presence 
of  minute  amounts  of  acids  and  alkalis  or  of  car- 
bolic acid,  strains  may  be  so  altered  that  they  lose 
permanently  the  ability  to  produce  spores.  Under 
favorable  conditions  the  spores  germinate  com- 
pletely in  from  three-quarters  to  one  and  one-half 
hours  (Grethe)  by  a  process  in  which  they  lose 
their  refractive  appearance  and  assume  first  an 
oval  and  then  a  rod  shape.  In  the  body  a  capsule 
surrounds  the  bacillus,  and  it  grows  singly  or  in 
very  short  chains ;  in  culture  media  it  is  very  diffi- 
cult to  obtain  capsules.  The  long  threads  which' 
appear  in  culture  media,  especially  bouillon,  are- 
not  found  in  infected  animals. 


494 


INFECTION     AND     IMMUNITY 


Resistance 

and   Virn- 

lence. 


Infection 
Atria. 


The  bacillus  itself  shows  no  unusual  resistance, 
but  its  spores  are  more  resistant  than  those  of  any 
other  pathogenic  bacterium.  When  dried  on  a 
thread  they  have  been  known  to  live  for  from  ten 
to  twelve  years.  Corrosive  sublimate  (1-2000) 
kills  them  in  forty  minutes  (Fraenkel),  and  direct 
sunlight  in  about  100  hours  (Momont).  Bacillus 
'pyocyaneus,  streptococci,  staphylococci  and  the  ba- 
cillus of  Friedlander  are  said  to  antagonize  its 
growth,  and  Kettger  found  that  the  dried  B.  prodi- 
giosus  decreased  the  virulence  of  the  organism  for 
animals  when  the  two  were  injected. 

The  anthrax  bacillus  is  remarkable  for  its  infec- 
tiousness. A  twenty-millionth  of  a  loop  of  a  viru- 
lent culture  will  cause  a  fatal  infection  in  mice, 
guinea-pigs  and  rabbits,  when  given  subcutaneous- 
ly.  A  systemic  infection  may  be  produced  by  feed- 
ing the  spores  or  causing  animals  to  inhale  them. 
The  gastric  juice  is  able  to  kill  the  bacilli,  but  not 
the  spores,  which  germinate  after  they  reach  the 
intestines. 

The  organism  is  distributed  by  the  excretions 
of  diseased  animals,  and  after  their  death  the  ad- 
jacent soil  becomes  heavily  infected  by  the  dis- 
charges which  escape  from  the  intestines  and  blad- 
der. In  this  situation  the  bacilli  pass  into  the 
sporing  stage,  in  which  they  remain  viable  and 
virulent  for  a  long  time. 

The  infection  of  herds  usually  is  accomplished 
by  the  ingestion  of  spores  which  have  been  distrib- 
uted in  this  way,  the  spores  germinating,  as  de- 
scribed above,  after  they  have  reached  the  intes- 
tines. The  disease  may  be  primary  in  the  skin  in 
the  form  of  malignant  pustule.  In  man  malignant 
pustule  is  the  commonest  type  of  infection,  occur- 


ANTHRAX. 


495 


ring  especially  among  those  who  have  to  do  with 
cattle  and  sheep.  The  bacilli,  however,  may  gain 
entrance  through  the  lungs  as  in  the  so-called 
"wool-sorter^s^^  disease,  which  is  caused  by  the  in- 
halation of  infected  dust  from  the  raw  material. 

The  generalized  infection  in  all  animals  is  rapid- 
ly fatal  (one  to  three  days),  and  the  occurrence  of 
death  is  sometimes  so  sudden  as  to  be  called  apo- 
plectiform; in  man  the  mortality  is  about  50  per 
cent.  Malignant  pustule  runs  a  more  favorable 
course. 

The  general  infections  are  marked  by  symptoms  Toxin. 
of  intense  intoxication  and  acute  degenerative 
changes  are  produced  in  the  parenchymatous  or- 
gans. Massive  numbers  of  the  bacilli  are  found  in 
the  blood.  Neither  a  soluble  toxin  nor  an  endo- 
toxin characteristic  for  the  organism  has  been  dem- 
onstrated up  to  the  present  time  (Sobernheim), 
although  there  is  abundant  clinical  and  anatomic 
evidence  of  intense  intoxication.  The  production 
of  mechanical  injuries  by  the  large  masses  of  ba- 
cilli in  the  circulation  is  doubtful. 

Eational  prophylaxis  involves  the  proper  dispo-  Prophylaxis. 
sal  of  the  bodies  of  animals  which  have  died  of 
anthrax,  the  exclusion  of  animals  from  fields 
known  to  be  infected,  suitable  disinfection  of  stalls, 
and  finally  protective  inoculation  against  the  dis- 
ease. Xo  part  of  the  anthrax  cadaver  should  be 
used  for  commercial  purposes,  because  of  the  dan- 
ger of  infecting  those  who  work  with  the  raw  ma- 
terials. Cleanliness  and  the  usual  precautions 
agaiTist  contagious  diseases  should  be  observed  by 
those  who  are  exposed  to  infection,  bearing  in  mind 
that  the  disease  may  be  transmitted  by  way  of  the 
lungs  and  alimentary  tract,  as  well  as  by  the  skin. 


bility. 


490  INFECTION     AND     IMMUNITY. 

Natural  im-  It  is  probable  that  no  disease  is  more  perplexing 
suseepti-  from  the  standpoint  of  immunity  than  anthrax. 
The  variations  in  susceptibility  and  immunity 
among  different  animals  are  extreme:  Guinea- 
pigs^  rabbits  and  mice  are  probably  more  suscepti- 
ble than  sheep  and  cattle;  compared  with  these  the 
dog  and  rat  are  relatively  immune,  whereas  fowls 
and  cold-blooded  animals  can  be  infected  with  dif- 
iiculty.  Although  the  microbe  is  readily  killed  by 
suitable  serums  (rabbit,  e.  g.),  such  an  effect  is  not 
an  index  of  immunity.  The  serum  of  the  highly 
susceptible  rabbit  is  strongly  bactericidal  in  test- 
glass  experiments,  whereas  that  of  the  more  resist- 
ant dog,  or  rat,  has  little  or  no  bactericidal  power. 
Because  of  this  inconsistent  relationship  of  the 
serum  to  immunity,  and  since  the  leucocytes  have 
a  high  phagocytic  power  for  the  anthrax  bacillus, 
Ptruschky,  Frank  and  others  agree  with  Metchni- 
koff  in  assigning  variations  in  the  natural  immun- 
ity of  different  animals  to  variations  in  phago- 
cytic power.  Bail  and  Pettersson,  in  extensive  ex- 
perimental work,  discovered  conditions  which,  they 
believe,  explain  the  lack  of  correspondence  between 
serum  properties  and  natural  immunity.  In  the 
serum  of  the  relatively  immune  dog  and  chicken 
they  found  bactericidal  amboceptors  but  no  com- 
plement; hence,  the  serum  could  show  no  bacteri- 
cidal action  in  the  test-glass.  If,  however,  leuco- 
cytes from  the  same  animals  were  added  to  the 
serum,  the  latter  became  bactericidal.  It  may  be 
assumed  that  in  the  course  of  infection  the  ambo- 
ceptors are  activated  by  complement  which  is  dis- 
charged from  the  leucocytes.  The  failure  of  the 
bactericidal  substances  of  the  rabbit's  serum  to 
protect  the  animal  was  ascribed  to  the  ability  of 


VACCINATION     IN     ANTHRAX.  497 

the  tissues  to  absorb  the  amboceptors  (Sobern- 
heim).  Their  work  is  of  sufficient  importance  to 
demand  repetition. 

Wright  has  shown  the  importance  of  the  opsonins 
for  phagocytosis  of  the  anthrax  bacillus. 

Eecovery  from  spontaneous  infection  is  said  to 
confer  a  degree  of  immunity,  which,  however,  is 
not  permanent. 

Artificial  immunity  may  be  produced  by  active   vaccination. 
or  passive  immunization.     The  first  attempts  at  * 

vaccination  were  made  in  1880  by  Toussaint,  who 
injected  the  blood  of  infected  animals  after  it  had 
been  heated  to  55  degrees  for  ten  minutes.  The 
bacilli  were  thus  attenuated,  but  they  were  able  to 
form  spores  subsequently  and  vaccination  was  not 
always  successful.  Pasteur  used  two  vaccines.  Vac- 
cine I  consisted  of  a  culture  which  was  attenuated 
by  growth  at  42°  C,  and  which  contained  no 
spores.  Vaccine  II  was  a  virulent  culture,  and  was 
injected  in  from  ten  to  fourteen  days  after  vac- 
cine I.  Its  use  is  said  to  have  caused  a  decrease 
in  anthrax  in  heavily  infected  districts,  with  a  con- 
sequent decrease  of  the  disease  in  man.  Various 
modifications  of  the  vaccines  of  Pasteur  have  been 
devised  by  others,  and  they  seem  to  be  equally  suc- 
cessful. In  some  instances  killed  bacilli  and  the 
products  of  bacterial  growth  have  been  used  with 
less  success.  The  Anthracase-Immunproteidin  of 
V.  Emmerich  and  LoAve  is  not  of  established  value. 

Immune  serum  for  therapeutic  purposes  is  pre-   serotiierapy 

■*■  •'--'•  ■*■  and  Propliy- 

pared  by  immunization,  first  with  killed  or  atten-  laxis. 
uated  cultures  and  then  with  virulent  strains.    The 
two  vaccines  of  Pasteur  may  be  used.     Although 
the  serum  has  been  shown  to  have  fairly  strong 


498  INFECTION     AND     IMMUNITY. 

protective  powers,  it  is  of  less  value  when  used  for 
curative  purposes.  It  produces  no  effect  after  the 
blood  stream  has  been  invaded  by  the  bacilli.  Its 
greatest  value  is  for  the  protection  of  herds  when 
anthrax  has  declared  itself.  In  man  it  has  been 
used  chiefly  in  the  treatment  of  malignant  pustule 
in  which  the  prognosis,  even  without  specific  treat- 
ment, is  not  unfavorable.  The  best  known  serums 
are  those  of  Sclavo,  prepared  from  the  goat  and  ass, 
of  Mendez  and  Deutsch.  The  properties  on  which 
the  value  of  the  serums  depends  are  unknown.  So- 
bernheim  is  very  positive  in  stating  that  the  bac- 
tericidal power  of  an  animal's  serum  is  not  in- 
creased by  immunization  or  infection,  and  the  ex- 
istence of  an  antitoxin  is  not  recognized.  As  in 
some  other  instances  immunization  may  cause  an 
increase  in  opsonins  which  would  render  the  serum 
effective  by  its  power  to  cause  increased  phagocy- 
tosis. 
Mixed  im-  The  mctliod  of  Sobernheim,  that  of  mixed  active 
and  passive  immunization,  seems  to  be  successful 
ation.  ^g  r^  prophylactic  measure.  The  vaccine  consists 
of  a  mixture  of  antiserum  and  bacilli.  Immune 
and  even  normal  serums  at  times  may  agglutinate 
the  anthrax  bacillus,  but  the  reaction  is  inconstant, 
and  the  ability  of  an  immune  serum  to  cause  ag- 
glutination is  no  index  of  its  protective  power.  Ag- 
glutination is  somewhat  difficult  of  determination 
because  of  the  tendency  of  the  bacillus  to  grow  in 
the  form  of  chains. 

II.    MALTA  FEVER. 

Malta,  Mediterranean  or  undulant  fever,  discovered 
in  the  Island  of  Malta,  also  occurs  among  British 
troops  at  Gibraltar,  and  cases  have  been  discovered 


mnnization 
and  Agr^lnti- 


MALTA     FEVER.  499 

in  the  Caribbean  Sea,  Porto  Eico,  in  Hongkong, 
Manila,  and  in  India.  Historically,  it  has  been 
traced  to  the  beginning  of  the  nineteenth  century, 
but  it  was  first  described  as  an  independent  disease 
by  Marsten  in  1859.  It  is  said  to  be  extending. 
The  disease  usually  runs  a  long  course,  which  is 
somewhat  typhoidal  in  character,  and  there  may  be 
one  or  more  relapses.  The  spleen  is  enlarged,  but 
the  intestines  are  not  involved. 

"It  is  distinguished  from  typhoid  by  its  long  du- 
ration, sometimes  extending  over  many  months; 
by  a  course  of  fever  exhibiting  marked  undula- 
tions; by  the  occurrence  of  copious  perspirations; 
by  the  frequent  appearance  of  rheumatic  articular 
disorders  as  well  as  by  neuralgia  and  inflammation 
of  the  scrotum  and  epididymis"  (Scheube).  It 
occurs  especially  in  the  summer  months.  The 
incubation  period  is  about  fifteen  days. 

Basset-Smith  found  the  serum  in  practically  all 
stages  of  the  disease  and  in  convalescence  to  have 
little  or  no  bactericidal  power  for  the  coccus.  Nor- 
mal serum  appeared  to  be  more  bactericidal  than 
that  of  the  patients,  although  such  an  action  was 
often  missed  in  normal  serum.  Wright  says  that 
normal  human  serum  is  devoid  of  bactericidal 
power  for  the  organism.  Basset-Smith  also  con- 
cluded that  the  phagocytic  power  of  the  patient^s 
leucocytes  is  less  than  in  the  case  of  normal  leuco- 
cytes. According  to  Wright,  the  organism  "is  em- 
inently sensible  to  the  opsonic  action  of  the  nor- 
mal serum,'^  under  the  influence  of  which  it  is 
taken  up  in  large  numbers  by  the  leucocytes. 

Agglutination  by  the  serums  of  patients  takes 
place  in   dilutions  varying  from  1-300  to  1-2000 


500  INFECTION     AND     IMMUNITY. 

or  even  as  high  as  1-6000.  Agglutinins  develop 
fairly  earl}^  in  the  course  of  the  infection,  and  the 
test  is  of  great  diagnostic  importance.  They  dis- 
appear in  about  two  years  after  recovery  (Birt  and 
Lamb ) . 

Bacillus  melitensis,  discovered  by  Bruce  (1887) 
in  the  spleen  of  patients  who  had  died  of  the  dis- 
ease, is  a  minute  organism,  slightly  oval  in  shape. 
According  to  Gordon,  it  possesses  one  flagellum, 
rarely  two  or  four,  and  is  slighth-  motile.  The 
bacillus  is  found  in  pure  cultures  in  the  spleen, 
which  is  greatly  enlarged.  Its  growth  in  culture 
media  is  very  slow. 

It  is  thought  that  infected  water  may  be  one 
means  of  transmission  of  the  disease.  Laboratory 
infections  with  pure  cultures  have  occurred 
through  small  wounds  resulting  in  typical  attacks 
of  Malta  fever  (Birt  and  Lamb).  The  disease  is 
not  transmitted  from  person  to  person. 

Up  to  the  present  time  the  monkey  is  the  only 
animal  known  with  susceptibility  to  artificial  infec- 
tion, although  the  organism  has  a  certain  viru- 
lence for  rabbits  and  guinea-pigs  on  intraperito- 
neal or  intracerebral  injection   (Durham). 

One  attack  confers  immunity,  which  may  disap- 
pear, however,  after  some  time  (Hughes). 

An  immune  serum  which  was  prepared  by 
Wright  is  said  to  influence  favorably  the  course  of 
the  disease. 


CHAPTER  XXVI. 
GROUP  in. 


Acute  infectious  diseases  in  which  acquired  im- 
munity of  prolonged  duration  is  not  established. 
In  some  instances  soluble  toxins  are  produced 
which  are  of  unknown  importance  in  the  infections 
(staphylococcus^  streptococcus).  Some  of  the  or- 
ganisms contain  rather  strong  endotoxins  (pneu- 
mococcus^  gonococcus),  whereas  in  others  a  reason- 
able basis  for  their  infectiousness  is  not  at  hand. 
In  some  instances  immunization  causes  increased 
resistance  to  infection  (staphylococcus,  streptococ- 
cus), whereas  this  property  has  not  been  fully 
demonstrated  in  others.^  The  serums  of  immun- 
ized animals  may  or  may  not  be  protective  for 
other  animals.  Those  organisms  which  cause  sys- 
temic infection  give  rise  to  leucocytosis  (except 
influenza).  Local  inflammations  are  accompanied 
by  the  accumulation  of  polymorphonuclear  leuco- 
cytes. 

I.     PNEUMOCOCCUS    INFECTIONS PNEUMONIA. 

No  one  organism  is  the  exclusive  cause  of  any  organisms 
one  type  of  pneumonia,  except  perhaps  the  viruses  pncTimonia. 
of  syphilis  and  tuberculosis.     Any  microbe  which 
causes  pneumonia  can  also  set  up  inflammations 
in  other  organs.     The  following  may  cause  acute 

1.  This  point  is  diflBcult  of  determination  wtien  an  organ- 
Ism  has  little  or  no  pathogenicity  for  animals  (influenza, 
gonococcus,   bacillus  of  Ducrey,   etc.). 


502  lyFECTION     Ayn     niMUMTY. 

pulmonitis:  Diplococcus  pneumonioe.  Streptococ- 
cus pyogenes,  Staphylococcus  pyogenes,  bacillus  of 
Friedlander  (B.  pneunionice) ,  B.  influenzce,  B.  pes- 
tis,  B.  diplitlieriw,  B.  typhosus,  B.  coli  communis, 
B.  tuherculosis  and  Micrococcus  catarrlialis.  The 
organisms  of  tuberculosis,  actinomycosis,  syphilis 
and  some  other  infections  cause  chronic  inflamma- 
tions of  the  lungs.  Some  of  these  organisms  have 
already  been  considered  and  others  will  be  dis- 
cussed later,  in  their  relation  to  pneumonia,  with- 
out, however,  entering  into  details  as  to  the  various 

Dipiococen.s  fvpcs  of  the  discasc.  The  Diplococcus  vneumonice 
IS  the  commonest  cause  of  lobar  pneumonia.  It 
produces  lobular  pneumonia  not  infrequently,  and 
has  been  found  as  the  onlv  oro;anism  in  acute 
interstitial  pneumonia   (Weichselbaum). 

Friedlander  (1882)  found  that  capsulated  cocci 
were  present  constantly  in  the  exudate  of  pneumo- 
nia. Such  cocci  in  all  probability  represented  the 
organism  which  at  present  is  known  as  the  pneu- 
mococcus,  yet  the  cultures  which  he  obtained  some- 
what later  showed  the  characteristics  of  the  organ- 
ism noAv  known  as  the  bacillus  of  Friedlander. 
Fraenkel,  in  1884,  obtained  the  first-named  coccus 
in  pure  culture,  and  his  investigations,  together 
with  those  of  Weichselbaum  and  many  others, 
eventually  established  the  independence  of  the 
two  organisms. 

Typical  and  The  typical  pueumococcus  is  slightly  elongated, 
""'strainH.  and  both  in  the  tissues  and  in  culture  media  it 
grows  in  pairs.  Typically,  also,  the  pair  possesses 
a  capsule  which  is  present  constantly  in  the  tissues 
and  may  be  obtained  on  certain  culture  media 
(milk  and  serum).  It  is  non-motile,  non-flagel- 
Intod.  forms  no  spores  and  stains  by  Gram's  method. 


rXEUMOCOCCUS. 


503 


Kather  scant  growth  occurs  on  the  ordinary 
culture  media  in  the  form  of  small  colonies  which 
resemble  those  of  the  streptococcus,  and  unless  spe- 
cial media  are  used  it  usually  can  not  be  carried 
through  many  generations.  When  grown  in  spu- 
tum, or  on  a  medium  which  contains  ascitic  fluid, 
the  blood  or  serum  of  man  or  some  favorable  ani- 
mal, its  virulence  may  be  preserved  for  some  time. 
By  growth  at  39°  C.  virulence  is  lost  rapidly. 
Strains  which  are  atypical  in  one  of  several  ways 
are  encountered.  They  may  show  low  virulence, 
may  grow  well  at  ordinary  temperatures  (the  typi- 
cal organism  not  doing  so),  may  produce  long 
chains  in  liquid  media,  or  may  grow"  without  a 
capsule. 

Recently  the  danger  of  confusing  the  pneumo-   confusion 
coccus  with  the  streptococcus  has  received  renewed  strepto- 
attention,   and   newer   methods   of   differentiation   *^***^*''**- 
render  it  extremely  probable  that  such  confusion 
has  occurred  in  the  past.    An  important  differen- 
tial method  is  that  of  cultivation  on  agar  plates 
which  contain  blood  (Schottmliller  and  Eosenow)  ; 
the  streptococcus  produces  a  clear  zone  of  hemo- 
lyzed   corpuscles   about  its   colonies,   whereas   the 
colonies  of  the  pneumococcus  present  a  greenish 
color  and  produce  no  hemolysis.     In  using  this 
test  G.  F.  Ruediger  found  a  surprising  number  of 
pneimiococci  in  normal  throats,  whereas  previous 
work  had  shown  them  to  be  less  common  than 
streptococci. 

In  spite  of  the  poor  viability  of  the  organism  on   Resistance. 
ordinary  culture  media,  it  is  fairly  resistant  to 
desiccation  and  sunlight,  especially  when  embedded 
in  sputum.    It  is  possible  that  the  surrounding  spu- 
tum is  protective  and  that  the  well-formed  capsule 


504  INFECTION     AND     IMMUNITY. 

which  the  coccus  possesses  as  a  parasite,  increases  its 
resistance.  When  dried  and  powdered  it  is  much 
less  resistant,  being  killed  by  direct  sunlight  in 
about  an  hour.  Like  other  bacteria,  it  resists 
diffuse  sunlight  better  than  direct,  and  in  the 
former  may  live  for  as  long  as  55  days  in  a  dried 
state  (Bordoni-Uffreduzzi,  cited  by  Weichsel- 
baum).  It  has  very  little  resistance  to  heat,  being 
killed  by  a  temperature  of  52°  C.  for  ten  minutes. 
Toxic  No  characteristic  soluble  toxin  ha?  been  obtained, 
although  more  or  less  poisonous  substances,  some 
of  them  of  a  chemical  nature,  have  been,  described. 
Presumably  the  toxic  properties  reside  in  an  endo- 
toxin. The  pneumotoxin  of  F.  and  G.  Klemperer 
was  prepared  by  precipitation  with  alcohol.  The 
pneumococcus  is  a  pyogenic  organism  and  causes 
exudates  which  are  rich  in  fibrin.  Occasionally 
serous  rather  than  purulent  exudates  are  produced. 
Its  toxic  action  is  directed  toward  various  organs, 
and  it  is  doubtful  if  any  of  the  tissues  of  the  body 
are  non-susceptible.  Some  strains  are  supposed  to 
be  more  neurotoxic  than  others. 

suRcepti-       The    susceptibility    of    animals    varies    greatly. 

AnimaiN.  Rabbits  and  mice  are  extremely  susceptible  and  are 
used  as  test  animals  for  the  identification  of  the 
organism.  Other  laboratory  animals  have  greater 
resistance,  and  the  pigeon  and  chicken  are  almost 
absolutely  immune.  In  susceptible  animals  a  rap- 
idly fatal  coccemia  or  more  or  less  extensive  local 
lesions  are  produced,  depending  on  the  virulence  of 
the  culture,  the  seat  of  inoculation  and  the  suscep- 
tibility of  the  animal.  In  rabbits  lobar  pneumonia 
has  been  produced  by  inoculation  into  the  pleura, 
trachea,  blood  stream  or  subcutaneous  tissue. 


VIRULENCE. 


505 


Eosenow  and  others  have  sliown  that   virulent   virulence. 
pnenmococci  are  much  less  susceptible  to  phago- 
cvtosis  than  are  non-virulent  strains. 

By  autolysis  the  substance  on  which  the  non- 
susceptibility  of  virulent  pneuniococci  to  phago- 
cytosis depends^  can  be  removed  and  in  this  man- 
ner virulent  pneuniococci  rendered  readily  phago- 
C3^table.  Furthermore,    by    treating    avirulent 

strains  of  organisms  with  the  autolytic  products 
of  virulent  organisms,  the  readily  phagocy table 
non-virulent  pneuniococci  can  be  rendered  less 
susceptible  to  phagocytosis.  This  substance,  which 
can  be  extracted  from  pneumococci  and  on  Avhich 
the  resistance  to  ]3hagocytosis  depends,  Eosenow 
has  called  ^^virulin."  Virulin  resists  boiling  for 
two  minutes  and  is  insoluble  in  alcohol  and  ether. 

The  pneumococcus  is  present  in  the  nose,  mouth  o 
and  pharynx  of  a  large  percentage  of  individuals 
It  is  encountered  more  frequently  in  crowded  cities 
than  in  country  districts.  It  persists  for  weeks 
and  months  in  the  mouths  of  convalescents  from 
pneumonia,  and  it  reaches  the  mouths  of  those 
who  are  in  the  vicinity  of  pneumonics.  It  is  found 
frequently  in  the  conjunctiva  and  occasionally  in 
the  deeper  air  passages.  That  it  may  reach  the 
stomach  and  intestines  with  the  sputum  is  appar- 
ent, and  it  has  been  found  there  as  the  cause  of 
diphtheric  enteritis,  a  condition  which  may  be 
followed  by  pneumococcus  peritonitis  or  general 
infection. 

The   lungs   are   infected   by   inhalation   of   the  Entrance 
cocci.     Suspended  in  droplets  of  saliva  or  mucus,  *"  **  i^'mss. 
or  adherent  to  foreign  particles,  they  may  be  car- 
ried fairly  deeply  into  the  bronchial  tubes.     That 
they  ever  reach  the  alveoli  by  this  means  alone  is 


cenrrence 
in  the  Body. 


50G  IXFECTIO^     AND     IMMUNITY. 

questioned  by  many.  Two  factors  would  seem  to 
prevent  their  being  carried  to  the  alveoli  by  cur- 
rents of  inspired  air:  First,  foreign  bodies  or  in- 
fected droplets  are  likely  to  strike  and  adhere  to 
the  walls  of  the  respiratory  passages  before  they 
have  traversed  a  great  length,  and  from  this  situa- 
tion may  again  be  carried  out  by  the  action  of  the 
ciliated  epithelium  or  coughing;  the  tortuous  pas- 
sages of  the  nose  and  its  hairs  and  moist  surfaces 
arrest  many  micro-organisms.  Second,  the  velocity 
of  the  inspired  air  is  greatly  reduced  or  is  nil  by 
the  time  the  particles  might  have  reached  the 
alveoli,  a  condition  which  renders  their  arrest  all 
the  more  probable.  Nevertheless,  pneumococci  do 
reach  the  alveoli,  and  by  some  it  is  supposed  that 
even  in  health  they  are  carried  there  more  or  less 
constantly  and  are  as  constantly  destroyed.  Occa- 
sionally they  have  been  found  in  the  parenchyma- 
tous tissue  of  the  lungs  of  individuals  who  have 
died  of  other  than  pneumococcus  infections  or  of 
non-infectious  diseases.  In  order  to  show  that 
micro-organisms  may  be  carried  into  the  paren- 
chyma by  inspiration  Nenninger  allowed  animals 
to  inhale  a  spray  containing  Micrococcus  prodigio- 
sus,  and  killing  the  animals  after  one-half  hour, 
was  able  to  cultivate  the  coccus  from  the  base  of 
the  lungs  where  only  alveoli  and  the  finest  bron- 
chial branches  were  present  (cited  by  Weichsel- 
baum). 
Lymphogren-  Various  othcr  agencies  have  been  suggested  by 
Hematoiaren-  which  the  cocci  may  be  carried  to  the  parenchyma- 
t"ons'  tous  tissue.  For  example,  during  the  forced  res- 
piratory efforts  which  accompany  coughing  they 
may  be  carried  from  tlie  bronchial  branches  into 
the  alveoli.     Or  the  organisms  having  reached  the 


INFECTION     IN     PNEUMONIA.  507 

bronchi,  may  be  carried  through  the  walls  of  the 
latter,  perhaps  by  the  leucocytes,  and  reach  the 
alveoli  directly  through  the  lymph  channels  or 
after  having  caused  infection  in  the  peribronchial 
lymph  glands.  Others  express  the  opinion  that 
pneumonia  follows  blood  infection  in  many  or 
most  instances,  i.  e.,  that  the  infection  is  hemato- 
genous, the  cocci  having  reached  the  blood  in  some 
obscure  manner.  That  the  infection  may  be  hem- 
atogenous is  shown  by  the  occasional  occurrence  of 
pneumonia  secondary  to  pneumococcus  infection  in 
other  parts  of  the  body. 

Knowing  the  fairly  constant  presence  of  pneu-  conditions 

.    .        ,,  .       ,  •11         for   Infection. 

mococci  m  the  upper  respiratory  passages  m  the 
normal  individual,  it  seems  certain  that  some  un- 
usual condition  must  arise  to  precipitate  infection 
of  the  pulmonary  tissue.  Concerning  the  nature 
of  these  conditions,  we  have  little  but  theories. 
They  may  rest  either  with  the  microbe  or  the  in- 
dividual, or  with  both.  The  pneumococci  which 
are  normally  on  the  mucous  surfaces  may  undergo 
an  increase  in  virulence,  or  more  virulent  organ- 
isms from  the  outer  world,  or  from  pneumonic  pa- 
tients, may  be  inhaled.  The  latter  condition  is  an 
important  one  in  relation  to  the  contagiousness  of 
pneumonia  and  the  development  of  epidemics. 
Park  and  Williams  found  a  larger  percentage  of 
virulent  organisms  in  the  sputum  of  pneumonics 
than  in  that  of  normal  persons.  It  is  possible  that 
the  pneumococcus  in  being  passed  from  one  patient 
to  another  undergoes  an  increase  in  virulence,  sim- 
ilar to  the  increase  which  may  be  obtained  by  pass- 
ing bacteria  through  animals. 

On  the  other  hand,  it  is  very  probable  that  es-  Decrease  of 
sential    changes    take    place    in    the    individual,  ^«»»*»*a"c«- 


508  IXFECTWy     AXD     IMMUMTY. 

changes  which  in  some  may  cause  the  lowered  re- 
sistance which  is  so  often  referred  to  as  a  condition 
for  infection.  Exposure  to  cold  has  long  been 
known  as  an  important  predisposing  factor,  al- 
though w^e  continue  in  ignorance  of  its  precise 
effects.  Animals  are  more  susceptible  to  pneumo- 
coccus  infection  after  artificial  reduction  of  the 
body  temperature.  It  is  possible  that  a  lowered 
body  temperature  may  decrease  antibacterial  ac- 
tivities; that  the  activity  of  the  bactericidal  fer- 
ments of  the  plasma  or  of  the  leucocytes  may  be 
suppressed,  or  phagocytosis  may  be  inhibited  so 
that  organisms  which  reach  the  bronchi  and  peri- 
bronchial lymphatic  structures  are  allowed  to  pro- 
liferate. It  is  probable  that  in  health  the  leuco- 
cytes continuously  pass  through  the  bronchial  and 
alveolar  walls  where  they  may  englobe  foreign  par- 
ticles (coal  dust)  or  bacteria,  and  leucocytes  are 
present  on  the  mucous  membranes  of  the  mouth 
cavity.  Following  exposure  and  the  reduction  of 
the  body  temperature,  or  following  the  prolonged 
inspiration  of  cold  air,  the  activity  of  the  phago- 
cytes may  be  inhibited  so  that  cocci  which  reach 
these  surfaces  are  not  ingested  and  continue  to 
proliferate,  or  the  same  conditions  may  decrease 
the  exudation  of  the  leucocytes  from  the  vessels. 
It  is  possible  also  that  the  activity  of  the  ciliated 
epithelium  is  reduced  similarly  so  that  the  cocci 
are  not  so  readily  carried  to  the  exterior. 
other  Extreme  exposure  is  not  always  followed  by 
Factors,  pucumonia,  however,  and  not  all  cases  oi  pneumo- 
nia are  preceded  by  exposure;  many  other  condi- 
tions may  predispose  to  infection,  as  a  lowered 
resistance  due  to  alcoholism,  other  infections  or  to 
non-infectious  processes.     That  certain  local  con- 


COMPLICATIONS.  509 

ditions  may  favor  infection  is  indicated  by  the  fre- 
quency with  which  individuals  with  chronic  tuber- 
culosis of  the  lungs  die  of  pneumococcus  pneumo- 
nia, and  the  development  of  the  disease  in  areas 
of  hypostatic  congestion.  Age  is  of  influence.  ''To 
the  sixth  year  the  predisposition  to  pneumonia  is 
marked;  it  diminishes  to  the  fifteenth  year,  but 
then  for  each  subsequent  decade  it  increases" 
(Osier).  The  cause  of  these  variations  is  not 
known^  although  the  rise  in  later  years  may  be 
associated  with  increased  exposure. 

The  conditions  which  predispose  to  infection  are 
now  the  subject  of  active  study  in  many  labora- 
tories, and  the  commission  which  the  New  York 
Department  of  Health  established  for  the  study  of 
acute  respiratory  diseases  made  important  observa- 
tions as  to  the  prevalence  and  virulence  of  pneu mo- 
cocci. 

Many  observers  have  found  pneumococci  in  the  compiica- 
blood  in  a  large  percentage  of  the  cases,  and  recent 
work  by  Eosenow  indicates  that  the  blood  is  prob- 
ably infected  in  all  cases  at  some  stage  of  the  dis- 
ease. This  being  the  case,  the  frequency  with  which 
pneumococcus  infections  occur  in  other  organs  as 
complications  of  pneumonia  is  readily  understood. 
Pleuritis  is  present  almost  constantly,  pericarditis 
frequently,  and  the  peritoneal  cavity  is  invaded  not 
infrequently  by  way  of  the  diaphragm,  with  general 
peritonitis  as  the  occasional  result.  In  pneumo- 
coccus pleuritis  the  exudate  is  frequently  of  a 
serous  character.  Endocarditis,  meningitis  and 
arthritis  are  frequent  complications.  Conjunctivi- 
tis, otitis  media,  cutaneous  or  subcutaneous  infec- 
tions,  intramuscular   abscesses    and    osteomyelitis 


510  IXFECTION     AND     IMMUNITY. 

may  develop.    The  kidne3's  and  liver  usually  show 
acute  degenerations. 

Diplococcus  pneumonia  occurs  as  a  complication 
in  typhoid,  diphtheria,  tuberculosis,  influenza,  ery- 
sipelas and  other  infections,  the  organism  of  the 
primary  infection  also  being  found  in  the  lungs. 
Not  infrequently  staphylococci,,  streptococci.  Mi- 
crococcus catarrlialis,  or  the  bacillus  of  Friedland- 
er,  are  found  with  the  pneumococcus,  the  latter 
being  the  predominating  organism.  Eecent  work 
from  Phipps'  Institute  (Flick,  Eavenell  and  Er- 
win)  suggests  that  the  pneumococcus  may  be  an 
exciting  cause  of  pulmonary  hemorrhage  in  the 
tuberculous. 

Prophylaxis.  Propliylactic  mcasures  are  largely  of  an  individ- 
ual character.  One  should  not  come  in  contact  un- 
necessarily with  those  suffering  from  pneumonia. 
The  susceptible  should  be  guarded  against  expos- 
ure; pneumonia  should  be  considered  as  a  conta- 
gious disease,  the  patients  should  be  isolated,  the 
sputum  disinfected,  and  rooms  cleaned  with  moist 
antiseptics  rather  than  by  dusting  and  sweeping; 
the  sick  room  should  be  flooded  with  sunlight,  and 
tlie  mouths  of  convalescents  disinfected.  Expecto- 
ration in  public  places  should  be  limited.  To  what 
extent  the  dust-laden  atmosphere  which  prevails 
in  most  of  our  large  cities  is  a  factor  in  causing 
pneumonia  is  unknown.  Vaccination  is  not  yet 
an  established  procedure. 
immnnity       It  is  probable  that  the   susceptibility   of  man 

and  s.nscep-  ^.^^.-^g  g^-gatly.     Under  equal  conditions  of  expos- 
ure not  all  contract  pneumonia,  and  an  individual 
,  who   eventually   contracts   the   disease   may   have 

undergone    many    similar    exposures    previously. 
Klemperer  introduced  a  culture  of  the  pneumococ- 


RECOVERY.  511 

ciis  which  was  virulent  for  rabbits  under  his  skin 
without  suffering  more  than  temporary  disturb- 
ance. 

Recovery  seems  to  indicate  an  acquired  immun-  Recovery. 
ity  or  resistance  which  is  by  no  means  permanent, 
and  often  is  of  very  short  duration.  One  may  have 
as  many  as  eight  or  ten  attacks  of  pneumonia,  the 
intervals  between  attacks  being  from  three  to  five 
years  on  the  average  (Griswolle).  What  the  re- 
covery or  acquired  resistance  depends  on  is  a  mat- 
ter of  much  discussion. 

Neufeld  and  Haendel  believe  that  the  antibodies 
in  pneumonia  are  inactive  until  a  certain  concen- 
tration is  reached  and  that  when  a  high  enough 
development  of  antibodies  occurs,  there  is  a  sudden 
neutralization  of  toxins  with  destruction  of  pneu- 
mococci  leading  to  the  crisis.  These  authors  find 
that  the  serum  of  patients,  who  have  passed  the 
crisis,  is  protective  for  mice  against  many  fatal 
doses  of  pneumococci.  Other  observers  have  failed 
to  find  any  evidence  that  the  crisis  is  due  to  anti- 
body production.  The  marked  leucocytosis  of 
pneumonia,  and  the  known  phagocytic  power  of 
the  leucocytes  for  the  diplococcus,  suggest  stronsfly 
the  importance  of  the  leucocytes  for  recovery.  The 
serums  of  convalescents  and  of  immune  animals 
show  no  increased  bactericidal  power  for  the 
organism,  nor  are  they  strikingly  antitoxic.  The 
opsonic  power  of  the  serum  in  pneumonia  is 
decreased  in  the  early  stages  of  the  disease  and 
reaches  its  height  at  the  crisis  and  the  following 
few  days. 

Some  of  the  serums  which  have  been  prepared  serotherapy 
have  been  used  therapeutically  in  man,  but  the  re-  ation. 
suits  have  not  been  sufficiently  satisfactory  to  put 


Roenier. 


512  INFECTION     AND     IMMUNITY. 

them  on  a  good  basis,  although  some  favorable  re- 
ports have  been  given. 
Serum  of  The  serum  of  Eoemer  is  obtained  by  immuniz- 
ing different  kinds  of  animals  with  several  strains 
of  pneumococci.  The  receptor  apparatus  of  differ- 
ent strains  probably  differ ;  hence,  a  serum  obtained 
by  immunization  with  several  strains  probably 
would  be  effective  against  a  large  variety  of  pneu- 
mococci. Furthermore,  since  different  animals 
may  respond  to  immunization  with  a  given  organ- 
ism by  the  formation  of  amboceptors  with  different 
complementophilous  haptophores,  a  theoretical  ad- 
vantage is  to  be  gained  by  mixing  immune  serums 
from  several  animals.  The  amboceptors  of  one  or 
more  of  the  serums  may  be  susceptible  to  activa- 
tion by  the  complement  of  the  patient's  body, 
whereas  if  only  one  serum  were  used  the  chance  of 
such  activation  would  be  decreased.  Passler,  in 
summing  up  the  results  obtained  in  the  treatment 
of  24  cases  with  this  serum,  finds  the  course  of  the 
disease  shortened,  the  temperature  reduced  and  a 
tendency  to  limit  the  extension  of  the  disease  to 
other  parts  of  the  lungs.  According  to  Neufeld 
and  Haendel  the  disadvantage  of  the  various  anti- 
serums lies  in  the  fact  that  they  cannot  readily  be 
given  in  large  enough  doses  to  be  effective. 

The  serum  of  pneumonia  patients  shows  an  in- 
creased agglutinating  power  for  the  pneumococcus. 
The  maximum  is  reached  at  or  near  the  time  of 
crisis,  but  rarely  has  a  higher  value  than  1  to  50 
to  1  to  60  (Neufeld,  Eosenow).  It  disappears 
quickly  after  recovery.  In  immunized  animals  the 
agglutinating  power  may  be  pushed  to  much  higher 
limits.  Not  all  strains  yield  agglutinins  equally, 
and  not  all  are  agglutinated  equally  by  the  same 


ation. 


TREATMENT.  513 

serum.  According  to  Collins^  pneumococci  fall 
into  different  groups,  depending  on  their  agglu- 
tinable  properties;  the  same  author  determined 
the  presence  of  group  agglutinins  in  an  immune 
serum.  ISTeufeld  states  that  avirulent  strains  were 
not  agglutinated  by  the  serum  of  pneumonic  pa- 
tients. 

Beginning  with  Fraenkel  (1886),  many  have  vaccine 
shown  the  possibility  of  increasing  the  resistance 
of  susceptible  animals  to  the  pneumococcus  by  in- 
jecting first  dead  or  avirulent  and  then  virulent 
cultures;  in  this  way  the  subjects  can  be  made  to 
withstand  many  multiples  of  the  minimum  fatal 
doses.  Eosenow  has  been  able  to  separate,  by  a 
process  of  autolysis,  the  more  toxic  part  of  the 
pneumococcus,  and  the  bodies  of  the  organisms. 
By  the  use  of  the  non-toxic  part  as  antigen,  a 
more  rapid  development  of  antibodies  can  be 
obtained,  experimentally,  than  can  be  accom- 
plished with  whole  pneumococci;  Eosenow  has 
made  this  fact  the  basis  of  treatment  of  pneu- 
monia by  means  of  injection  of  the  autolyzed  bod- 
ies of  pneumococci  and  has  obtained  encouraging 
results.  It  is  hoped  that  this  procedure  will  be  a 
valuable  aid  in  hastening  the  crisis. 

OTHER  INFECTIONS  BY  THE  PNEUMOCOCCUS. 

Complicating  infections  by  the  pneumococcus 
during  the  course  of  pneumonia  were  mentioned 
above.  They  may  occur  by  way  of  the  lymph 
channels,  as  in  pleuritis,  pericarditis  and  peritoni- 
tis (through  the  diaphragm),  by  continuous  exten- 
sion, as  in  infection  of  the  bronchi,  nose  and,  per- 
haps, the  middle  ear,  or  as  metastatic  infections 
following  the  invasion  of  the  blood  stream  by  the 


Infection. 


514  INFECTION     AND     IMMUNITY. 

organisms.  It  is  undoubtedly  in  the  last  named 
manner  that  meningitis^  endocarditis,  arthritis, 
and  muscular  and  subcutaneous  abscesses  arise. 

Eosenow  has  isolated  from  endocarditis  cases 
pneumococci  differing  from  the  usual  type  in  that 
they  gi'ow  in  clumps  and  adhere  more  or  less 
closely  to  the  surface  of  blood-agar  slants.  They 
grow  in  chains  and  produce  less  green  on  blood- 
agar  plates  than  do  pneumococci  of  the  usual  type. 
In  animal  inoculation  a  tendency  to  localize  on 
endotlielial  surfaces  is  shown. 
Mode  of  other  infections  by  the  pneumococcus  occur  in- 
dependent of  the  existence  of  pneumonia.  Such 
conditions  are  alveolar  abscesses,  conjunctivitis, 
dacryocystitis,  serpent  ulcer  of  the  cornea,  in- 
flammation of  the  middle  ear,  meningitis,  enteri- 
tis, rarely  peritonitis,  and  pneumococcus  septice- 
mia which  may  be  complicated  by  infection  in  vari- 
ous organs.  The  eye  is  exposed  to  infection  from 
without  and  the  ear  from  the  pharynx.  Primary 
pneumococcus  meningitis  occurs  both  sporadically 
and  epidemically,  although  the  meningococcus  is 
a  much  more  frequent  cause.  The  organisms  may 
gain  entrance  through  the  middle  ear  or  nose,  or 
through  the  circulation  from  a  primary  focus  in 
another  organ,  perhaps  an  undiscovered  focus.  Pre- 
ceding and  during  meningitis  the  nose  is  not  in- 
frequently the  seat  of  pneumococcus  rhinitis,  and 
the  organisms  may  be  carried  from  the  nose  to  the 
meninges  by  way  of  the  lymph  channels.  The 
blood  may  be  infected  secondarily.  Pneumococcus 
meningitis  is  almost  invariably  fatal.  The  organ- 
ism causes  chronic  meningitis  less  frequently  than 
the  meningococcus.     Infection  of  the  peritoneum 


STREPTOCOCCUS.  515 

may  follow  an  intestinal  infection ;  a  pure  pneumo- 
coccns  infection  of  the  peritoneum  in  the  absence 
of  pneumonia  is  extremely  rare.  Pneumococcus 
infections  of  the  eye,  ear,  intestines  and  perito- 
neum are  likely  to  be  accompanied  by  other  or- 
ganisms. 

Pneumococcus  conjunctivitis  occurs  in  epidemic 
form  and  the  same  precautions  should  be  taken 
to  limit  it  as  for  the  limitation  of  influenza  con- 
junctivitis. 

Serpiginous  ulcer  of  the  eye,  a  progressive  phag- 
edenic process  in  the  cornea,  is  usually  caused  by 
the  pneumococcus,  although  other  organisms  may 
be  present.  Eoemer  treats  the  condition  with 
an  antipneumococcus  serum  and  claims  that  he  is 
able  to  arrest  the  process  if  the  treatment  is  begun 
sufficiently  early.  The  serum  is  injected  beneath 
the  conjunctiva. 

II.   STREPTOCOCCI. 

When  wound  infections,  cases  of  septicemia  and  Discovery  oft 

Pyosfcnlc 

pyemia  were  first  studied  bacteriologically,  various  cocci. 
names  were  applied  to  certain  cocci  which  were 
found.  Such  were  the  Microsporon  septicum  of 
Klebs  and  the  Coccohacteria  septica  of  Billroth 
and  others.  Pasteur  recognized  such  organisms 
and  cultivated  them  at  an  early  date,  but  Ogsten, 
in  1880  to  1884,  using  the  newly-devised  technic 
of  Koch,  was  the  first  to  recognize  two  sorts  of 
pyogenic  cocci,  to  which  he  gave  the  names  of  strep- 
tococci and  staphylococci.  The  former  grew  in  the 
form  of  chains  and  the  latter  in  clusters.  In  1883 
Fehleisen  obtained  the  streptococcus  in  pure  cul- 
tures from  cases  of  erysipelas.  Eosenbach  deter- 
mined more  exactly  the  significance  of  streptococci 


516  INFECTION     AND     IMMUNITY. 

in  wound  infections  and  septicemia,  and  gave  to 
the  organism  the  name  of  Streptococcus  pyogenes. 
Morphology.  The  tjpical  streptococcus  is  a  spherical  or 
spheroidal  cell,  about  one  micron  in  diameter, 
which  grows  in  the  form  of  chains  of  varying 
length.  Division  takes  place  in  one  direction 
only.  Variations  in  form,  such  as  diplococcus-like 
cells  in  pairs  or  chains,  or  elongated  cells  resem- 
bling bacilli,  represent  accidental  stages  or  anoma- 
lies in  division.  Streptococci  commonly  appear  as 
diplococci  in  the  blood  and  tissues  of  the  infected. 
Unusually  large  cells  may  be  involution  forms. 
The  difficulty  of  distinguishing  the  pneumococcus 
from  the  streptococcus  has  been  mentioned.  At 
one  time  it  was  thought  that  streptococci  could 
be  separated  into  those  which  grew  in  long  chains 
(S.  longus)  and  those  which  produce  short  chains 
{S.  brevis) .  Although  these  names  are  still  used 
for  convenience,  they  are  not  well  grounded,  since 
the  length  of  the  chains  is  not  an  inherent  prop- 
erty; one  form  may  be  changed  into  the  other  by 
appropriate  methods  of  cultivation.  Similarly  the 
S.  erysipelatis  of  Fehleisen  is  not  a  specific  or- 
ganism for  erysipelas,  since  strains  from  other 
sources  are  able  to  cause  experimental  erysipelas 
in  man.  Streptococci  growing  in  short  chains  may 
be  cultivated  from  the  normal  mouth  cavity  and 
they  are  usually  of  low  virulence  for  animals.  On 
the  other  hand,  S.  longus  is  more  often  obtained 
from  wound  infections,  septicemia  and  malignant 
tonsillitis.  Capsulated  strains  of  high  virulence 
are  occasionally  found  in  the  body.  Ordinarily, 
however,  streptococci  are  not  surrounded  by  a  cap- 
sule. The  Streptococcus  mucosus  may  be  a  pneu- 
mococcus.     Although    streptococci    are    described 


STREPTOCOCCUS. 


517 


which  do  not  stain  by  Gram's  method,  those  with 
which  we  are  concerned  invariably  react  positively. 
Streptococci  are  never  motile,  possess  no  fiagellse 
and  form  no  spores. 

Streptococci  grow  better  in  a  neutral  or  slightly 
alkaline  medium  than  in  one  of  acid  reaction,  but 
virulence  is  lost  rapidly.  They  may  be  cultivated 
indefinitely  in  media  which  contain  serum  or 
ascitic  fluid,  but  even  here  virulence  disappears 
gradually;  frequent  transplantation  is  necessary. 
In  bouillon  those  strains  which  produce  short 
chains  or  grow  as  diplococci  cause  a  diffuse  cloud- 
ing of  the  medium,  whereas  those  growing  in  long 
chains  sink  to  the  bottom,  leaving  a  clear  overly- 
ing fluid.  Streptococci  demand  little  oxygen,  all 
are  facultative  anaerobes  and  some  are  said  to  be 
obligate  anaerobes;  obligate  anaerobes  may  be  cul- 
tivated from  the  vagina  and  intestines.  The 
optimum  temperature  for  growth  is  37°  C. 

When  dried,  streptococci  live  for  from  ten  days 
to  several  weeks;  they  are  destroyed  more  quickly 
in  the  presence  of  sunlight.  Susceptibility  to 
antiseptics  depends  on  the  nature  of  the  medium 
in  which  they  are  suspended  or  imbedded.  When 
unprotected  by  bouillon  or  other  fluid  they  are 
killed  in  a  few  seconds  by  1/1000  corrosive  sub- 
limate and  3  per  cent,  carbolic  acid  (Fehleisen)  ; 
when  in  bouillon,  by  1/1500  corrosive  sublimate 
and  by  1/200  carbolic  acid  in  fifteen  minutes.  Ly- 
ing on  a  mucous  surface,  where  they  are  imbedded 
in  mucus  or  tissue  fluids,  they  are  protected 
against  antiseptics  to  some  extent.  They  are  fairly 
resistant  to  heat,  being  destroyed  by  a  temperature 
of  70°  to  75°  C.  in  one  hour  (v.  Lingelsheim ) . 


Cultivation. 


Resistance. 


518 


INFECTION     AND     IMMUNITY. 


Virulence.  Streptococci  varj  widely  in  their  pathogenicity. 
Cultures  which  are  entirely  non-pathogenic  for 
animals  are  frequently  cultivated  from  nature  and 
from  man.  As  a  rule,  however,  the  long  chains 
obtained  from  pathological  processes  in  lAan  are 
pathogenic  for  rabbits  and  mice.  Their  virulence 
is  very  labile,  and  by  passage  through  suitable  ani- 
mals (rabbit,  mouse)  it  may  be  pushed  to  a  very 
high  point;  in  doing  this,  however,  the  original 
virulence  of  the  culture  undergoes  modifications. 
For  example,  Marmorek  so  increased  the  virulence 
of  one  strain  that  the  millionth  part  of  a  cubic 
centimeter  was  fatal  for  rabbits,  but  it  had  lost  its 
pathogenicity  for  man,  as  shown  by  inoculations 
into  carcinomatous  patients.  Hence  the  patho- 
genicity of  cultures  for  animals  is  not  a  good 
index  of  their  virulence  for  man.  Those  which 
produce  long  chains  in  bouillon  are  more  patho- 
genic than  those  forming  short  chains  (v.  Lingel- 
sheim). 

Rabbits  and  mice  are  the  most  susceptible  ani- 
mals. The  rat,  guinea-pig  and  cat,  and  larger  ani- 
mals, as  the  horse,  goat  and  sheep,  are  less  sus- 
ceptible. A  bouillon  culture  of  which  from  0.01 
to  1.0  c.c.  will  kill  a  mouse  or  rabbit  in  from  one 
to  four  days  is  considered  of  high  to  moderate 
virulence.  Virulent  cultures  cause  systemic  infec- 
tion, regardless  of  the  method  of  inoculation. 
Less  virulent  cultures  produce  changes  which  are 
more  localized  in  character  and  which  may  heal : 
abscesses,  areas  of  necrosis  and  er3^sipelatous 
inflammations. 

Bndetoxin.  The  properties  on  which  the  virulence  of  strepto- 
cocci depends  are  little  understood.  The  conflict 
of  opinion  concerning  many  points  probably  de- 


STREPTOCOLYSIN.  519 

pends  on  the  use  of  different  strains  of  the  organ- 
ism in  experimental  work.  The  amount  of  endo- 
toxin which  virulent  strains  contain  is  subject  to 
great  variations.  Aronson  found  practically  none 
in  the  killed  cells  of  a  very  virulent  strain.  It 
seems  probable  that  the  endotoxin  is  rather  sus- 
ceptible to  heat^  since  cultures  which  are  killed 
by  mild  methods,  as  by  chloroform,  are  more  toxic 
than  those  which  are  killed  by  heat.  The  filtrates 
of  old  bouillon  cultures  are  more  or  less  toxic.  A 
strong  "toxin"  was  prepared  by  Marmorek  by 
growing  a  virulent  strain  in  a  mixture  of  serum 
and  bouillon  for  three  months  and  filtering  the 
culture.  More  recently  he  uses  a  medium  contain- 
ing glycocol  and  leucin.  Toxic  precipitates  from 
fluid  cultures  have  also  been  obtained.  Bouillon 
filtrates  of  virulent  cultures  after  two  to  fourteen 
days  of  growth  have  low  toxicity  (Aronson). 

Besredka,  and  later  G.  F.  Euediger,  showed  that  streptoco- 
virulent  streptococci  produce  a  hemolytic  toxin  Leucocytic 
when  grown  in  various  heated  serums.  Euediger 
proved  that  this  hemolysin  (streptocolysin)  is  a 
true  toxin,  possessing  a  haptophorous  and  toxo- 
phorous  structure.  This  discovery  has  an  im- 
portant bearing  on  the  fact  that  the  blood  in  fatal 
streptococcus  infections,  especially  in  rabbits,  is 
often  more  or  less  laked.  Streptocolysin  is  de- 
stroyed by  a  temperature  of  70°  C.  in  two  hours, 
by  peptic  digestion,  deteriorates  rapidly  at  ordi- 
nary temperatures,  and  is  non-dialysable.  Certain 
normal  serums  contain  antistreptocolysin  (Eue- 
diger). Another  significant  fact  is  that  virulent 
strains,  when  grown  in  serum  and  ascitic  fluid, 
produce  a  substance  which  kills  leucocvtes  and 
inhibits  phagocytosis.     This  may  explain  the  fail- 


Toxin. 


Processes. 


520  INFECTION     AND     IMMUNITY. 

\ire  of  leucocytes  to  take  up  virulent  organisms, 
whereas  non-virulent  strains  are  readily  phagocy- 
tized.  Von  Lingelsheim  states  that  strains  culti- 
vated from  subacute  or  chronic  processes  produce 
more  soluble  toxin  (nature  unknown)  than  highly 
virulent  strains.  Not  all  toxic  filtrates  contain 
streptocolysin,  the  hemolysin  being  independent 
of  other  toxic  constituents  (Simon).  Von  Lingels- 
heim concludes  that  the  infectiousness  of  strepto- 
cocci is  not  explained  by  the  toxic  properties  which 
have  been  demonstrated.  He  lays  stress  on  their 
resistance  to  the  bactericidal  activities  of  the  tis- 
sues and  tissue  fluids.  It  is  safe  to  say  that  up  to 
the  present  time  the  essential  toxin  of  the  strepto- 
coccus has  not  been  demonstrated. 
Pathologic  Streptococci  are  the  frequent  cause  of  wound  in- 
fections, the  most  common  cause  of  lymphangitis 
and  diffuse  inflammations  of  the  subcutaneous  and 
intermuscular  connective  tissues  (cellulitis),  endo- 
metritis and  puerperal  septicemia,  endocarditis 
and  tonsillitis,  are  often  the  exciting  organisms 
in  pneumonia  (lobular,  usually),  bronchitis, 
meningitis,  inflammations  of  the  serous  surfaces 
(pericardium,  pleura,  peritoneum  joints),  enteritis 
and  suppurative  processes  in  the  middle  ear.  They 
are  the  exclusive  cause  of  erysipelas,  and  serious 
attempts  have  been  made  to  show  that  they  are 
etiologic  factors  in  scarlet  fever  and  rheumatic 
fever.  The  streptococcus  is  the  most  common 
organism  found  in  the  lesions  of  impetigo  conta- 
giosa, although  it  may  be  mixed  with  other  bac- 
teria, especially  the  staphylococcus.  Occurring  as 
mixed  infections  in  pneumonia,  tuberculosis,  scar- 
let fever,  enteritis  and  other  processes,  they  cause 
grave  and  often  fatal  complications. 


ERYSIPELAS.  521 

Not  all  streptococci  are  able  to  cause  erysipelas, 
and  a  streptococcus  cultivated  from  a  case  of  ery- 
sipelas is  not  able  to  cause  the  disease  in  all  indi-  Erysipelas. 

viduals.  Furthermore,  cultures  obtained  from 
other  sources  (phlegmon)  may  produce  the  dis- 
ease (Koch  and  Petruschky).  Koch  produced  an 
erysipelatous  inflammation  with  staphylococcus. 
It  has  been  suggested  that  streptococci  which 
cause  erysipelas,  rather  than  some  other  process, 
do  so  because  of  some  peculiarity  in  their  virulence 
or  in  the  resistance  of  the  individual,  or  perhaps 
both.  Another  suggestion  is  that  this  type  of  in- 
fection depends  on  some  peculiarity  in  the  skin 
and  subcutaneous  tissue  of  the  susceptible.  The 
conditions  are  obscure.  The  infection  atrium  is 
not  always  known.  In  facial  erysipelas  entrance 
probably  is  gained  through  the  mucous  membrane 
of  the  nose  in  many  instances.  Erysipelas  is  a 
wound  infection  in  most  or  all  instances,  although 
the  atrium  often  escapes  observation.  The  cocci 
lie  principally  in  the  lymph  spaces  and  interspaces 
of  the  connective  tissue.  They  are  rarely  to  be 
cultivated  from  the  scales  or  the  fluid  of  blisters, 
but  may  be  obtained  from  skin  which  is  excised 
from  the  border  of  the  inflamed  area  (Fehleisen). 
They  probably  are  not  excreted  through  the  un- 
broken skin. 

Erysipelas  is  an  inflammation  of  the  superficial  i.ymphan- 
lymphatics  of  the  skin,  while  in  lymphangitis  the  *****•• 
deeper  lymphatics  are  involved.  Thrombosis  of 
the  lymphatic  vessels,  congestion  of  the  adjacent 
blood  vessels,  causing  reddened  streaks  and  local 
hemolysis  (?),  are  distinguishing  local  features. 
Metastases  occur  to  adjacent  lymph  glands  and 
the  infection  may  become  general.    In  this  process, 


522  INFECTION     AND     IMMUNITY. 

as  well  as  in  wound  infections,  thrombosis  of  the 
adjacent  vessels  may  occur,  which  may  be  the  first 
step  in  the  production  of  pyemia  with  multiple 
points  of  infection. 

Cellulitis  may  also  be  caused  by  the  staphylo- 
coccus alone  or  infection  with  the  latter  may  be 
superimposed  on  a  primary  streptococcus  cellulitis. 
Pnenmonia.  Pncumonia  produccd  by  the  streptococcus  may 
either  be  primary  or  secondary  to  infection  in 
other  parts  of  the  body.  It  is  mostly  of  the  lobular 
type  in  the  occurrence  of  multiple  foci,  which  pre- 
sent a  smooth  surface  on  section  and  are  very  rich 
in  cells.  It  occurs  less  frequently  in  the  form  of 
lobar  consolidation,  and  very  frequently  as  a  mixed 
infection  in  pneumonias  caused  by  the  pneumo- 
coccus  and  other  organisms. 

Streptococcus  infection  of  the  lungs  in  pul- 
monary tuberculosis  is  a  serious  and  frequent  com- 
plication of  the  latter  disease.  It  produces  a  septic 
condition,  involves  adjacent  healthy  tissue,  and  its 
role  in  causing  consolidation  and  liquefaction  of 
the  tissues  predisposes  of  hemorrhages.  In  cul- 
tures, the  streptococcus  is  said  to  inhi1)it  the 
growth  of  the  tubercle  bacillus. 
Meninsritis.  Primary  streptococcus  meningitis  is  rare  or  of 
doubtful  occurrence.  It  frequently  is  secondary 
to  otitis  media,  to  injuries,  and  has  been  noted 
following  tonsillitis,  facial  erysipelas,  pneumonia, 
endocarditis  and  as  part  of  a  pyemic  process. 
EnteritiM.  Strcptococci  are  at  times  the  cause  of  enteritis 
in  children,  the  inflammation  often  being  mem- 
branous and  accompanied  by  desquamation  of  the 
epithelium  and  by  hemorrhages.     It  is  not  infre- 


STREPTOCOCCUS     INFECTIONS.  523 

qiiently  followed  by  peritonitis  and  septicemia. 
Virulent  organisms  probably  reach  the  intestines 
through  milk  in  many  instances.  Escherich  found 
streptococci  in  nearly  every  sample  of  milk  which 
he  examined.  Digestive  disturbances  due  to  other 
causes  predispose  to  infection.  The  organisms  are 
nearly  always  present  in  the  intestines  of  the 
adultj  but  cause  enteritis  less  frequently  than  in 
children. 

The  normal  vagina  does  not  offer  a  good  cul-  and*r?emB. 
lure  medium  for  pathogenic  bacteria,  although 
streptococci  are  occasionally  found  there.  They 
occur  more  frequently  in  those  who  have  borne 
children.  The  vagina  tends  to  purify  itself  me- 
chanically and  by  the  acid  nature  of  its  secretions. 
If  the  secretion  for  any  reason  becomes  alkaline, 
as  in  catarrhal  conditions,  or  if  it  contains  blood 
and  serum,  w^hich  provide  a  good  culture  medium, 
virulent  streptococci  proliferate.  Infection  takes 
place  through  denuded  surfaces  and  tears;  endome- 
tritis, metritis,  parametritis,  salpingitis,  peri- 
tonitis and  sepsis  may  follow.  Thrombosis  of  the 
blood  vessels  may  be  followed  by  the  development 
of  pneumonic  foci. 

Streptococci  are  probably  alw^ays  present  on  the  ipper 

.,        ,-,  1  e   XI  ii  Respiratory 

tonsils,  the  mucous  membrane  oi  the  mouth,  very  passnsres. 
frequently  in  the  sputum  and  not  infrequently  on 
the  mucous  membrane  of  the  anterior  nares.  Pre- 
Piim.ablv  thev  proliferate  under  inflammatory  con- 
ditions from  whatever  cause,  finding  in  the  serum 
and  plasma  which  exude  a  medium  favorable  for 
growth  and  the  development  of  virulence.  They 
are  of  great  significance  in  severe  local  inflamma- 
tions, as  in  diphtheria  and  scarlatina,  and  when 


524  INFECTION     AND     IMMUNITY. 

general  resistance  is  lowered^  as  in  typhoid,  typhus, 
variola,  measles,  etc.  Von  Lingelsheim  character- 
izes their  relation  to  diphtheria  as  follows:  they 
injure  the  tissues  locally,  penetrate  beneath  the 
membrane  into  the  tissues  and  take  part  in  the 
formation  of  the  membrane;  they  increase  the 
virulence  of  the  diphtheria  bacillus;  alone,  or  in 
conjunction  with  the  diphtheria  bacillus,  they  may 
invade  the  lungs,  causing  bronchopneumonia,  or 
enter  the  circulation  and  injure  various  organs, 
but  particularly  the  kidneys.  Their  method  of 
entering  the  lungs  from  the  upper  respiratory  pas- 
sages probably  is  similar  to  that  involv^ed  in  pneu- 
mococcus  infection.  Furthermore,  having  obtained 
a  footing  in  the  pharynx,  for  example,  they  may 
reach  the  bronchi  and  perhaps  the  alveoli  by  exten- 
sion along  the  surface. 

Streptococci  are  usually  the  essential  organisms 
in  follicular  tonsillitis,  are  frequently  found  in 
alveolar  abscesses,  but  in  both  instances  may  be 
mixed  with  other  organisms,  especially  the  staphy- 
lococcus and  pneumococcus.  Streptococci  in  the 
throat  may  appear  in  diplococcus  form  in  fresh 
preparations.  Beginning  primarily  in  the  nose, 
tonsils  or  pharynx,  streptococcus  infection  may 
extend  to  the  adjacent  sinuses,  the  middle  ear, 
meninges,  or  through  the  tonsils  may  cause  sys- 
temic infection  with  endocarditis  as  a  frequent 
complication. 
Endocarditis.  The  cudocarditis  caused  by  streptococci  usually 
is  vegetative  in  character,  but  may  be  ulcerative^ 
and  may  result  in  metastatic  foci  of  infection 
(e.  g.,  septic  infarcts).  Infarcts  from  strepto- 
coccus endocarditis  are  not  always  infected,  how- 


RHEUMATIC     FEVER.  525 

ever.      Not   infrequently   the   vegetations   contain 
staph}' lococci  as  well  as  streptococci. 

Since  1867,  when  Salisbury  described  a  fungus  Rheumatic 
which  he  called Zymotosis  translucens, many  micro-  *^®^*''- 
organisms  have  been  described  and  cultivated  from 
the  joints,  blood,  endocarditic  and  pericarditic 
lesions  and  from  the  tonsils  in  acute  articular 
rheumatism.  Among  them  were  the  "Monadinen" 
of  Klebs  (1875),  short  bacilli  by  Wilson  (1885) 
and  others,  staphylococci  and  streptococci  by 
Welch selbaum  (1885)  and  by  many  others,  and 
an  anaerobic  bacillus  resembling  that  of  anthrax 
by  Achalme  (1890).  Streptococci  have  been  found 
more  frequently  than  other  organisms.  The  ba- 
cillus of  Achalme  acquired  considerable  prominence 
at  one  time,  being  found  in  rheumatism  in  a  num- 
ber of  cases,  but  it  has  been  found  since  in  other 
conditions,  and  normally,  and  Achalme  himself 
gave  up  his  original  claims  for  its  etiologic 
significance.  The  organism,  possibly,  is  identical 
with  B.  aerogenes  capsulatus  of  Welch  (Harris). 
Many  of  the  observations  are  of  little  value,  since 
the  cultures  were  made  postmortem,  when  contami- 
nations and  agonal  invasions  by  other  organisms 
could  not  be  excluded.  The  conditions  were  very 
confusing,  however,  since  the  injection  of  pure 
cultures  occasionally  produced  arthritis,  peri- 
carditis and  endocarditis  in  animals.  This  was 
the  case  with  a  short  anaerobic  bacillus  or  diplo- 
bacillus  cultivated  by  Thiroloix,  and  by  Triboulet, 
Coyon  and  Zadoc  (1897). 

In  1897-98  Triboulet  and  Coyon  cultivated  from 
the  blood  of  five  cases  of  rheumatic  fever  a  diplo^ 
coccus,   pure  cultures  of  which   caused   arthritis. 


526  INFECTION     AND     IMMUNITY. 

endocarditis,  etc.,  in  rabbits.  Similar  observations 
have  been  made  by  Westphal,  Wassermann  and 
Malkoff,  Poynton  and  Paine,  Beaton  and  Walker 
and  others,  and  the  possibility  of  producing  lesions 
characteristic  of  rheumatic  fever  by  the  inocula- 
tion of  pure  cultures  into  rabbits  has  been  well  es- 
tablished. Although  the  organism  was  called  a 
diplococcus  by  the  discoverers,  it  can  not  be  dis- 
tinguished from  the  ordinary  streptococcus  pyo- 
genes by  cultural  tests.  These  discoveries  do  not, 
however^  put  this  particular  streptococcus  on  a 
satisfactory  basis  as  the  cause  of  the  disease,  since 
streptococci  from  various  sources  are  able  to  cause 
experimental  arthritis  in  rabbits  (Cole,  Harris). 
It  seems  that  virulent  streptococci  from  whatever 
source  have  a  predilection  for  serous  surfaces.  This 
is  apparent  from  the  frequency  with  which  the 
joints,  endocardium,  etc.,  are  involved  in  strepto- 
coccus septicemia  in  man.  The  view  of  Singer 
and  of  Menzer  that  "acute  rheumatism  is  simply 
one  of  the  many  manifestations  of  streptococcus 
invasion"  (Harris),  finds  some  justification  in 
the  streptococcus  tonsillitis  with  which  the  dis- 
ease usually  begins,  the  recovery  of  streptococci 
from  the  lesions  and  the  production  of  these  lesions 
in  rabbits  by  the  injection  of  pure  culture?.  Tun- 
nicliff  found  that  the  opsonic  indices  foi-  M.  rheu- 
maticus  (Beattie,  Poynton  and  Paine)  for  Strep- 
tococcus viridans  from  tlie  thioat  of  a  patient  with 
rheumatism  and  for  Streptococcus  pyogenes  fol- 
low the  same  course  during  attacks  of  rheu- 
matism. In  cases  with  joint  symptoms  and 
high  temperature  the  index  was  subnormal  and 
with      in]])rovenu'nt      in      clinical      symptoms      it 


SCARLET     FEVER. 


527 


rose  above  normal. '  The  indices  for  Staphy- 
lococcus aureus,  pneiimococcus  and  a  strain  of 
Streptococcus  viridans  from  a  normal  throat 
did  not  show  a  variation  from  the  normal. 
Agglutinins  common  to  M.  rheumaticus  and  strep- 
tococci were  found  to  follow  the  same  course  as 
the  opsonic  index.  Immunization  of  rabbits  with 
M.  rheumaticus  resulted  in  the  formation  of  opso- 
nins for  both  this  organism  and  Streptococcus 
pyogenes.  These  findings  would  indicate  that 
streptococci  pla}^  an  essential  part  in  acute  articu- 
lar rheumatism.  The  fact  remains^  however,  that 
streptococci  cannot  always  be  cultivated  from  the 
lesions  of  rheumatic  fever ;  hence  it  is  possible  that 
the  organism  may  exist  as  a  mixed  infection  with 
more  or  less  constanc}^,  and  that  the  real  cause  is 
as  yet  unknown  (Phillip). 

The  theory  that  scarlet  fever  is  of  streptococcus  Relation  ot 
etiology    has    been    held     particularly    by    Babes,  to^lcariet^*^* 
Klein,  Moser,  Gordon  and  Baginsky  and  Sommer-  ^^^®''* 
feld.     Some  have  held   that  streptococci  isolated 
from  the  disease  show  distinctive  properties  and 
deserve  the  name  of  Streptococcus  scarlatince.  This, 
however,  is  not  agreed  to  by  most  bacteriologists, 
the  organisms  not  differing  from  streptococci  ob- 
tained from  various  sources.     The  organisms  are 
not  found  constantly  in  the  erythematous  eruption. 

Virulent  streptococci  are  found  on  the  tonsils 
almost  invariably  in  scarlet  fever.  In  65  per  cent, 
of  the  cases  a  membrane  is  formed  (Ranke),  and 
this  is  often  due  to  the  streptococcus,  which  is 
sometimes,  however,  associated  with  diphtheric 
infection.  The  frequency  with  which  streptococci 
invade  the  blood  during  scarlet  fever  is  related  to 
the  severity  of  the  disease.     Occasionally  they  are 


528  INFECTION     AND     IMMUNITY. 

found  in  mild  cases,  which  run  a  short,  uncompli- 
cated course,  but  "more  frequently  in  severe  and 
protracted  cases,  in  which  there  also  may  develop 
local  complications  and  clinical  signs  of  general 
infection,  such  as  joint  inflammations^'  (Hek- 
toen).  Baginsky  and  Sommerfeld  found  strepto- 
cocci in  the  blood  and  organs  of  each  of  eisrhtv- 
two  fatal  cases.  Hektoen  states,  however,  that 
streptococcemia  is  not  necessarily  present  in  fatal 
cases. 

Gabritschewski  and  other  Eussians  have  reported 
satisfactory  results  following  prophylactic  vacci- 
nation against  scarlet  fever  by  means  of  killed 
streptococci  from  scarlet  fever  patients.  They 
advance  this  experiment  as  an  argument  in  favor 
of  the  streptococcus  as  the  sole  cause  of  scarlet 
fever.  The  results,  however,  have  not  3^et  been 
confirmed  by  other  observers. 

At  present  there  is  not  sufficient  ground  for  con^ 
sidering  streptococci  as  the  specific  agent  in  scarlet 
fever,  although  they  are  undoubtedly  the  cause  of 
the  most  frequent  and  serious  complications.  The 
mortality  of  the  disease  probably  is  greatly  raised 
by  mixed  infections  with  the  streptococcus. 

Streptococcus  filtrates  or  cultures  may  cause  de- 
generative changes  in  the  spinal  cord  (Homen 
and  Laitinen). 
Beneficial  Certain  strains  of  streptococci  are  said  to  exer- 
cise a  curative  effect  in  experimental  anthrax. 
Von  Emmerich  and  di  Mattel  found  that  by  intra- 
venous injection  of  the  cocci  rabbits  could  be  saved 
from  an- anthrax  infection  which  otherwise  would 
prove  fatal  in  forty-eight  hours.  This  result  can 
not  always  be  obtained,  and  it  may  be  that  only 


IMMUNITY     TO     STREPTOCOCCUS.  52U 

certain  strains  have  this  effect  (Zagari,  cited  by 
V.  Lingelsheim).  It  is  noted  occasionally  that  lupus 
improves  or  actually  heals  following  an  attack 
of  erysipelas.  A  reputed  effect  of  a  similar  nature 
in  tuberculosis  of  the  lungs  was  mentioned  above. 

The  clinical  observation  that  an  attack  of 
erysipelas  often  causes  a  decrease  in  the  size  of  farco*im" 
malignant  tumors,  especially  sarcomas,  received 
some  confirmation  from  the  experimental  work  of 
Fehleisen.  With  the  hope  of  reproducing  erysipe- 
las with  pure  cultures,  Fehleisen  had  inoculated 
streptococci  into  those  suffering  from  such  tumors. 
Among  six  patients  so  inoculated,  a  decrease  in  the 
size  of  the  tumor  was  noted  in  five.  Killed  cul- 
tures were  tried  without  effect.  Coley's  mixture 
of  killed  cultures  of  the  streptococcus  and  Bacillus 
prodigiosus  received  rather  extensive  trial  as  a 
substitute  for  living  cultures  of  the  streptococcus, 
and  in  many  instances  improvement  and  even 
cures  have  been  reported.  Others  have  had  no 
favorable  results.  Senn  used  the  preparation  in 
twelve  cases  of  inoperable  sarcoma  "with  negative 
results.^'  The  Bacillus  prodigiosus  is  supposed  in 
some  way  to  increase  the  efficacy  of  the  strepto- 
coccus toxin;  it  contains  a  toxic  protein.  These 
toxins  seem  to  have  no  influence  on  carcinomas. 

Concerning  the  natural  susceptibility  and  im- 
munity of  man  to  infections  with  the  streptococcus  imMiunity 

•^  ^  and  Suscep- 

little  is  known.  It  seems  probable  that  the  un-  tibiiuy. 
impaired  mucous  surface  resists  invasion  by  the 
organisms  which  occur  constantly  in  the  mouth 
cavity;  the  physical  protection  of  the  intact  sur- 
face, the  rapid  desquamation  of  epithelium,  the 
rapid  excretion  with  the  saliva,  the  inhibiting  in- 
fluence of  the  saliva  on  the  proliferation  of  bac- 


530  INFECTION     AND     IMMUNITY. 

teria  and  the  destruction  of  bacteria  by  the  leuco- 
cytes which  constantly  appear  on  the  mucous  sur- 
face are  probably  important  factors  in  this  local 
resistance.  Congestion  of  these  surfaces,  espe- 
cially the  tonsils,  from  any  cause,  as  from  ex- 
posure, or  the  occurrence  of  some  other  infection, 
as  may  be  the  case  in  scarlet  fever,  may  lower  the 
local  protective  powers.  And,  as  stated,  the  serum 
and  plasma  which  exude  in  catarrhal  conditions 
or  otlier  inflammations,  provide  a  medium  which 
favors  the  growth  and  development  of  virulence 
by  streptococci. 

Concerning  the  conditions  which,  in  the  body, 
antagonize  infection,  we  are  largely  in  the  dark. 
It  has  been  impossible  to  demonstrate  antitoxic 
and  bactericidal  substances  in  the  normal  serum 
of  man.  Streptococci  grow  freely  in  fresh  normal 
serum  which  contains  no  leucocytes  (Weaver  and 
G.  F.  Euediger).  Phagocytosis  of  streptococci 
first  came  under  the  observation  of  Metchnikoff, 
who  in  1887  noted  it  as  a  striking  occurrence  in 
erysipelas.  Only  the  microphages  took  up  the  cocci. 
The  marked  leucocytosis  which  is  noted  clinically 
suggests,  but  of  course  does  not  prove,  that  the 
leucocytes  take  an  active  part  in  the  destruction 
of  the  cocci.  Experimental  work  showing  such  a 
relationship  is  not  lacking,  however.  Bordet  con- 
cluded that  all  the  protection  which  guinea-pigs 
and  rabbits  show  against  streptococci  is  due  to 
the  phagocytes.  In  actual  infection  streptococci 
have  often  been  found  within  the  leucocytes  of 
the  blood  and  inflammatory  exudates  (G.  F.  Rue- 
diger.)  Non-virulent  or  weakly  virulent  strains 
are  phagocytized  more  readily  than  the  virulent  in 
experimental   work.     Kuediger  also  demonstrated 


IMMUNIZATION     OF     ANIMALS.  531 

conclusively  that  the  streptococci  taken  up  by  poly- 
morphonuclear leucocytes  may  be  killed  by  the  lat- 
ter. Hence  the  evidence  in  favor  of  a  protective 
role  by  the  leucocytes  is  more  than  presumptive. 
Ruediger  suggests  the  importance  of  the  Icuco- 
cytic  toxin  of  the  streptococcus  for  the  develop- 
ment of  infection.  It  may  either  kill  the  leuco- 
cytes or  cause  negative  chemotaxis,  and  under  these  ' 
conditions  proliferation  of  the  cocci  may  proceed. 

Weaver,  Tunnicliff  and  Boughton  have  shown 
that  the  defense  of  the  body  against  streptococci 
depends  on  the  power  of  phagocytosis  on  the  part 
of  the  leucocytes  as  well  as  the  opsonin,  hence  the 
estimation  of  the  resisting  power  of  the  body  must 
be  measured  by  the  bactericidal  power  of  whole 
blood. 

The  streptococcus  usually  is  classed  with  those  Acquired 
organisms,  infection  with  which  does  not  cause  the 
development  of  lasting  immunity.  A  certain 
amount  of  immunity  probably  is  established,  how- 
ever. This  is  suggested  by  the  results  of  Fehlei- 
sen,  who  could  not  always  cause  second  attacks 
of  erysipelas  by  the  inoculation  of  pure  cultures 
into  the  susceptible.  It  is  also  suggested  by  the 
ease  with  which  relatively  high  resistance  caa  be 
produced  in  animals  by  brief  immunization.  A 
streptococcus  infection  of  the  horse  which  occurs 
naturally  ("Druse")  is  said  to  produce  immunity 
which  lasts  for  a  year  or  two. 

One  may  immunize  animals  either  with   toxic  immnnixa' 
filtrates  or  with  killed  and  living  cultures.     The  Animals. 
filtrates  are  much  less  effective  in  producing  im- 
munity than  the  bacterial  cells,  and  in  the  hands 
of  many  no  immunity  whatever  could  be  estab- 
lished. 


532  INFECTION     AND     IMMUNITY. 

A  number  of  different  principles  have  been  fol- 
lowed in  immunizing  with  cultures.  It  seems  that 
virulent  strains  cause  a  higher  degree  of  immunity 
and  a  serum  of  higher  protective  power  for  other 
animals  than  strains  of  low  virulence.  On  this 
account  Marmorek,  and  also  Aronson,  immunize 
horses  with  streptococci,  the  virulence  of  which  has 
been  pushed  to  a  very  high  point  by  passing  them 
through  rabbits.  Strong  resistance  is  induced  by 
this  method,  and  the  immune  serum,  particularly 
that  of  Aronson^  shows  distinct  protective  power 
for  other  animals.  Such  serums,  however,  have 
the  highest  protective  power  against  the  particu- 
lar strain  which  was  used  for  immunization,  al- 
though the  serum  of  Aronson  is  not  devoid  of  pro- 
tective powers  against  other  pathogenic  strains. 
Concerning  the  serum  of  Marmorek  there  are  di- 
vergent opinions.  In  the  hands  of  Marmorek  it 
is  highly  protective  in  animal  experiments;  others 
have  found  it  without  value.  The  method  of  Mar- 
unity  or  Mul-  morck  and  of  xA.ronson  rests  not  only  on  the  basis 
streptococci,  that  straius  of  the  highest  virulence  will  give  the 
strongest  serums,  but  also  on  the  assumption  of 
the  unity  of  all  pathogenic  streptococci.  If  all 
are  alike  in  their  biologic  and  pathogenic  proper- 
ties, a  serum  which  protects  against  one  should 
protect  against  all.  As  pointed  out,  there  is  at 
present  not  sufficient  ground  for  considering  the 
streptococci  of  erysipelas,  scarlet  fever,  rheuma- 
tism, sepsis,  etc.,  as  independent  species.  By  cul- 
tivation and  passage  it  is  possible  to  so  modify  any 
one  of  them  that  it  is  indistinguishable  from  the 
others,  on  the  basis  of  morphology  and  patho- 
genicity. On  the  other  hand  they  are  not  all 
identical  in  some  very  important  properties.     For 


8TREPT0C0C0IC     SERUMS.  533 

example^  not  all  strains  produce  hemolysin  to  the 
same  degree,  and  they  differ  greatly  in  their  sus- 
ceptibility to  the  action  of  an  agglutinating  serum. 
We  have  also  to  remember  that  pathogenicity  for 
animals  is  not  a  reliable  index  of  pathogenicity  for 
man.  From  these  confusing  conditions  we  can 
only  regard  the  question  of  unity  or  multiplicity 
of  streptococci  as  an  open  one,  which  may  be  de- 
cided by  future  investigations. 

The  serums  of  Marmorek  and  Aronson  are  uni-  univalent  aud 
valent  serums,  a  single  strain  being  used  for  im-  serums. 
munization.  Certain  investigators,  believing  in 
the  multiplicity  of  streptococci,  utilize  several 
strains  in  immunization.  The  serum  of  Denys  is 
obtained  by  immunizing  with  several  strains  the 
virulence  of  which  has  been  artificially  increased. 
Such  a  serum  would,  theoretically,  have  a  wider 
range  of  action  than  a  univalent  serum ;  it  is  poly- 
valent. Having  in  mind  the  fact  that  passing  a  cul- 
ture through  rabbits  increases  the  virulence  of 
the  organism  for  the  rabbit,  but  alters  its  virulence 
for  the  original  host  (man),  Tavel,  Moser  and 
Menzer  prepare  serums  on  a  different  basis. 
Tavel  employs  several  strains  of  streptococci  cul- 
tivated from  pathological  processes  in  man,  avoid- 
ing such  alterations  in  virulence  as  would  be  caused 
by  passing  the  cultures  through  animals.  On  the 
assumption  that  scarlet  fever  is  a  streptococcus 
disease,  Moser  immunizes  horses  with  strains 
(about  twenty)  which  are  cultivated  from  cases 
of  scarlet  fever.  In  a  similar  manner,  Menzer, 
supposing  that  rheumatic  fever  is  a  streptococcus 
infection,  immunizes  with  a  number  of  strains  cul- 
tivated from  the  tonsils  of  cases  of  rheumatism. 
Both  Moser  and  Menzer  avoid  passage  in  order  to 


534 


JNFECTlOy     AAZ>     IMMUNITY. 


Serani 
Protection. 


Serum 
Therapy. 


retain  tlie  original  biologic  properties  of  the  cul- 
tures. 

Jn  animal  experiments,  some  of  these  serums, 
and  particularly  that  of  Aronson,  have  exhibited 
strong  protective  powers.  Aronson^s  serum  in 
doses  of  0.0004  to  0.0005  c.c.  protects  a  mouse 
against  ten  fatal  doses  of  the  streptococcus  given 
twenty-four  hours  later  than  the  serum.  A  serum 
of  which  0.01  c.c.  protects  against  a  dose  known 
to  be  fatal  is  considered  of  normal  strength.  The 
present  serum,  then,  is  of  twenty-  to  twenty-five- 
fold value.  In  some  instances  animals  can  be 
saved  when  the  serum  is  used  some  hours  after 
infection,  but  this  period  is  a  brief  one. 

Statements  concerning  the  value  of  antistrepto- 
coccus  serums  in  treating  human  infections  are 
very  conflicting.  The  serum  of  Marmorek  has 
been  given  more  general  trial  than  any  other,  and 
the  results  have  not  been  satisfactory.  Favorable 
effects,  such  as  the  lowering  of  temperature  and 
improvement  in  the  general  condition,  have  been 
reported,  but  the  serum  possesses  no  distinct  cura- 
tive power  in  established  infections.  Koch  and 
Petruschky  deny  that  it  has  a  prophylactic  power 
in  experimental  erysipelas.  Escherich,  by  using 
the  serum  of  Moser,  and  Baginsky,  by  using  that 
Scarlet  of  Aronsou,  observed  a  shortening  of  the  course, 
Fever.  .^  reductiou  of  the  fever  and  general  improvement 
in  cases  of  scarlet  fever.  Moser  claims  that  it  re- 
duces the  mortality  of  the  disease.  The  use  of 
antistreptococcus  serum  in  the  treatment  of  scarlet 
fever  does  not  commit  one  to  the  streptococcus 
etiology  of  the  disease,  but  rather  to  the  impor- 
tance of  streptococcus  complications ;  hence,  if  the 
danger  of  these  complications  can  be  reduced  by 


UTREPTOCOCGIG     SERUMS. 


535 


antistreptococcus  serum  its  use  is  justified.  It 
remains  for  future  work  to  demonstrate  to  our 
satisfaction  that  it  has  such  value. 

What  has  been  said  concerning  the  treatment  of 
scarlet  fever  with  the  serums  of  Moser  and  Aron- 
son  also  applies  to  the  treatment  of  rheumatism 
with  the  serum  of  Menzer.  Favorable  reports  have 
appeared  concerning  its  value,  but  a  sufficient  mass 
of  experience  has  not  accumulated  to  permit  of 
satisfactory  judgment.  "So  much  appears  from 
observations  in  man  that  the  different  streptococcus 
serums  are  harmless'^  (Dieudonne). 

As  nearly  as  can  be  learned  at  present,  anti- 
streptococcus  serum  is  protective  (and  cura- 
tive (  ?)  )  because  of  its  ability  to  stimulate  phago- 
cytosis, rather  than  because  of  serum  antitoxins 
or  bacteriolysins.  This  was  indicated  by  the  ob- 
servations of  Bordet  in  animal  experiments,  in 
which  marked  phagocytosis  of  streptococci  took 
place  in  the  peritoneal  cavity  of  immunized  ani- 
mals, but  very  little  in  normal  animals.  A  simi- 
lar condition  was  noted  in  the  test-glass  experi- 
ments of  Denys  and  van  der  Velde.  A  mixture 
of  normal  rabbit  serum  and  leucocytes  showed 
very  little  phagocytosis  of  streptococci,  whereas 
the  addition  of  antistreptococcus  serum  caused 
active  phagocytosis,  with  death  of  the  cocci.  The 
presence  of  a  definite  substance  in  the  serum  which 
stimulated  phagocytosis  was  conceived  by  van  der 
Velde  and  also  by  v.  Lingelsheim.  It  was  heat- 
resistant  (62°  to  65°  C),  and  was  not  destroyed 
by  dilute  acids  and  alkalies  (cited  by  Lingelsheim). 

The  prophylactic  injection  of  killed  streptococci 
in  scarlet  fever  has  been  mentioned. 


Rlienniatiiiiii. 


Properties 
of  Serum. 


Stlmnlatioja 
of  Phagocy- 
tosis. 


Vaccine 
Tlierapy. 


nation. 


536  INFECTION     AND     IMMUNITY. 

Eeports  regarding  the  curative  injection  of 
streptococci  have  been  conflicting.  It  has  been 
found  that  the  use  of  galactose  as  a  means  of  kill- 
ing the  streptococci  results  in  a  better  preservation 
of  antigenic  properties  than  does  the  use  of  heat. 

Weaver  concludes  that  the  use  of  therapeutic 
injections  of  galactose-killed  streptococci  is  of 
value  only  in  subacute  and  chronic  streptococcus 
infections. 
Assinti-  The  agglutinability  of  streptococci  from  differ- 
ent sources,  and  even  from  the  same  source,  varies 
a  great  deal.  Also  the  normal  serums  of  man  and 
animals  have  a  variable  agglutinating  power  for 
different  strains  of  streptococci.  By  immunization 
with  a  given  strain  the  agglutinating  power  is  in- 
creased, but  not  uniformly  for  all  strains.  Com- 
monly the  strain  used  for  immunization  is  agglu- 
tinated more  strongly  than  heterologous  strains, 
the  latter  sometimes  undergoing  no  agglutination 
whatever.  These  variations  do  not  depend  on  dis- 
coverable differences  in  the  cocci  or  the  diseases 
which  they  produce.  A  given  antistreptococcus 
serum  does  not  agglutinate  equally  all  streptococci 
from  cases  of  scarlet  fever  (Weaver).  Also  strep- 
tococci vary  greatly  in  their  ability  to  stimulate 
to  the  formation  of  agglutinins.  On  the  whole 
those  which  produce  long  chains  are  more  suscep- 
tible to  agglutination  and  yield  stronger  serums 
than  those  with  short  chains  (Aronson,  Tavel, 
V.  Lingelsheim).  By  passage  the  agglutinating 
properties  undergo  rather  complex  changes.  The 
organism  then  produces  a  stronger  agglutinating 
serum  and  is  agglutinated  more  readily  by  this 
serum  than  the  same  strain  which  had  not  been 


AGGLUTINATION.  537 

passed  through  animals.  If  passage  is  discon- 
tinued it  reverts  to  its  former  condition. 

The  variations  are  such  that  the  agglutination 
reaction  is  of  little  or  no  value  in  differentiating 
different  types  of  streptococci. 

As  to  the  clinical  value  of  the  test  for  the  diag- 
nosis of  scarlet  fever,  the  conclusions  of  Weaver 
may  be  cited : 

1.  Of  streptococci  cultivated  from  cases  of  scar- 
latina, some  are  agglutinated  by  almost  all  scar- 
latinal sera,  but  at  dilutions  varying  from  1/60 
to  1/4000 ;  others  are  agglutinated  by  the  same 
sera  with  less  constancy  and  at  lower  dilutions,  and 
many  are  not  agglutinated  at  all. 

2.  Streptococci  cultivated  from  cases  of  scar- 
latina are  agglutinated  by  sera  from  cases  of  lobar 
pneumonia  and  erysipelas  at  about  the  same  dilu- 
tions as  by  scarlatinal  sera,  and  in  the  case  of  ery- 
sipelas even  at  higher  dilutions.  • 

3.  The  same  appears  to  be  true  of  typhoid  fever 
serum,  so  far  as  limited  tests  indicate,  and  to  al- 
most the  same  extent  of  puerperal-fever  serum. 

4.  The  agglutination  reaction  between  the 
streptococci  cultivated  from  cases  of  scarlatina  and 
the  serum  from  cases  of  scarlet  fever  is  in  no  way 
specific,  and  can  not  be  of  any  value  as  a  means  of 
diagnosis. 

By  growing  streptococci  on  a  medium  which 
contains  serum  (serum  bouillon),  they  form  fewer 
and  shorter  chains  and  are  better  suited  for  ag- 
glutination tests. 

III.      STAPHYLOCOCCI. 

staphylococci  are  spherical  cells  from  0.7  to  0.9 
microns  in  diameter,  typically,  and  by  light  stain- 


538 


INFECTION     AND     IMMUNITY 


Cultivation 

and  Blologrlc 

Properties. 


ing  are  often  seen  to  consist  of  two  hemispheres, 
which  are  separated  by  a  delicate  cleft.  In  pus 
they  are  found  in  small  groups  of  two  to  nine  or 
ten,  ocasionally  as  diplococci,  tetrads  or  very  short 
chains. 

They  are  luxuriant  growers  on  nearly  all  media 
which  are  suitable  for  bacteria,  preferring,  how- 
ever, a  slightly  alkaline  reaction.  Growth  is  best 
in  the  presence  of  oxygen,  but  proliferation  occurs 
in  its  absence.  Sputum,  serum  and  ascitic  fluid 
are  favorable  media,  and  in  the  last  two  the  cocci 
may  be  agglutinated.  An  alkaline  reaction  is  pro- 
duced in  litmus  milk,  and  the  casein  is  precipitated 
and  partly  digested.  The  production  of  a  proteo- 
lytic ferment  is  shown  by  liquefaction  of  gelatin 
and  the  formation  of  a  clear  zone  about  the  colo- 
Ferments.  j^^gg  -^vhen  grown  in  plates  which  contain  coagulat- 
ed serum  (Loeb,  cited  by  Neisser  and  Lipstein). 
Albumin  is  changed  into  peptone.  Loeb  distin- 
guishes between  a  ferment  which  liquefies  gelatin 
(gelatinase,  a  "coUolytic"  ferment),  and  one  which 
digests  albumen  (tryptic  ferment).  Gelatinase  is 
present  in  staphylococcus  filtrates  and  normal 
serums  are  rich  in  antibodies  for  it.  A  fat-splitting 
ferment  (lab  ferment)  is  also  present  in  the 
filtrates.  The  fact  that  the  pus  which  is  produced 
in  staphylococcus  infection  does  not  coagulate  may 
be  due  to  the  action  of  the  proteolytic  ferment, 
which  digests  the  fibrinogen. 

Van  der  Velde  had  noted  in  1894  that  '^staphy- 
lotoxin"  (staphylococcus  filtrates)  cause  hemoly- 
sis. Neisser  and  Wechsberg,  in  1901,  by  growing 
the  organisms  in  bouillon  of  suitable  alkalinity, 
obtained  hemolytic  filtrates,  giving  the  name  of 
staphylolysin  to  the  hemolytic  principle.  The  hemo- 


Staphylo- 
lysin 


LEUGOCIDIN.  539 

lytic  action  of  the  staphylococcus  is  readily  seen 
in  cultures  on  blood-agar  plates;  a  zone  of  hemo- 
lysis forms  about  the  colonies.  Erythrocytes  of  the 
rabbit,  when  placed  in  bouillon  cultures,  undergo 
hemolysis.  Staphylotoxin  also  produces  liemolysis 
in  the  living  body.  The  maximum  production  of 
staphylolysin  occurs  after  a  growth  of  nine  to 
fourteen  days  in  alkaline  bouillon,  and  nearly 
all  pathogenic  strains  yield  it,  whether  aureus, 
albus  or  citreus.  It  is  not  formed  by  non-patho- 
genic strains.  The  toxin  is  destroyed  by  exposure 
to  a  temperature  of  56°  C.  for  twenty  minutes.  A 
specific  antitoxin  is  present  in  many  normal 
serums  and  may  be  increased  by  immunization 
with  the  toxin  or  the  living  organisms. 

In  1894  van  der  Velde  found  in  the  pleural  Lencocidin. 
exudates  caused  by  inoculation  with  killed  cultures 
of  the  staphylococcus  a  substance  which  is  toxic 
for  leucocytes,  causing  them  to  swell  and  the  nuclei 
to  disappear.  This  substance  is  called  leucocidin. 
It  is  also  produced  in  culture  media,  but  the  ability 
to  form  it  is  not  so  widely  distributed  as  in  the 
case  of  the  hemolysin.  Leucocidin  is  a  true  toxin, 
like  the  hemolysin;  most  normal  serums  contain 
antileucocidin,  and  the  latter  is  increased  by  im- 
munization with  the  toxin.-     The  suo^orestion  is  a 

Co 

natural  one  that  leucocidin  may  be  a  factor  in 
combating  phagocytosis  in  infections  with  the 
staphylococcus.  ^N'eisser  and  Wechsberg  de- 
vised a  ^'^bioscopic  method'^  of  determining  the 
cytocidal  action  of  the  toxin.  Living  leucocytes, 
like  other  living  cells,  have  the  power  of  decoloriz- 
ing methylene  blue  when  ox3^gen  is  excluded.   The 

2.  Leucocidin  and  staphylolysin  will  not  yield  antitoxins 
when  their  activity  has  been  destroyed  by  heat. 


540 


INFECTION     AND     IMMUNITY. 


Toxie 
Filtrates. 


Endotoxin. 


Varieties  of 
Staphylo- 

<'OCC«H. 


destructive  action  of  the  toxin  on  the  leucocytes 
is  indicated  by  the  failure  of  this  reduction  when 
the  toxin  is  mixed  with  the  cells. 

Old  culture  filtrates  (two  to  three  weeks)  show 
a  rather  high  degree  of  toxicity  for  animals,  pro- 
ducing extensive  degeneration  of  the  convoluted 
tubules  in  the  kidney,  a  degeneration  which  is 
somewhat  selective;  hemorrhages  into  the  in- 
testinal mucosa;  degeneration  of  the  ganglionic 
cells,  and  fever.  According  to  Levaditi,  a  mast- 
cell  leucocytosis  develops.  The  nature  of  the  fever- 
producing  substance  is  unknown.  The  toxicity  of 
filtrates  is  said  to  be  destroyed  by  a  temperature 
of  56°  C. 

Cultures  of  the  staphylococcus  killed  by  heat 
show  little  toxicity,  hence  the  question  of  the  ex- 
istence of  an  endotoxin  is  on  no  better  basis  than 
in  relation  to  the  streptococcus.  It  is  possible  that 
the  heat  required  to  kill  the  organisms  destroys  the 
endotoxin  as  well  as  the  soluble  toxins  mentioned 
above.  The  virulence  of  the  organisms  has  no 
direct  relationship  to  the  hemolysin  or  leucocidin, 
or  the  toxicity  of  the  filtrates.  Very  pathogenic 
strains  may  produce  a  filtrate  of  little  or  no 
toxicity.  It  seems  then  that  the  essential  patho- 
genic agent  of  the  organism  is  unknown;  as  in 
the  case  of  the  streptococcus,  its  infectiousness 
depends  on  its  ability  to  resist  the  antibacterial 
activities  of  the  body  (phagocytic  and  digestive 
power  of  the  leucocytes  and  opsonins).  The  part 
played  by  the  leucocidin  in  this  resistance  is  not 
definitely  known. 

The  many  varieties  of  the  staphylococcus  are 
dilTerentiated  on  the  basis  of  pathogenicity,  pig- 
ment formation,  liquefaction   or  non-liquefaction 


STAPHYLOCOCCUS.  541 

of  gelatin,  and  other  cultural  properties.  The 
Staphylococcus  alhus  differs  from  the  Staphylo- 
coccus aureus  only  in  its  inability  to  form  pig- 
ment, and  it  cannot  be  made  to  acquire  this  prop- 
erty. Pigment  is  formed  most  abundantly  on 
potato,  whereas  little  is  formed  on  blood  serum. 
Other  pigment-forming  varieties  are:  S.  cereus 
flavus,  S.  pyogenes  citreus,  S.  scarlatinus  and 
Micrococcus  hematodes.  The  S.  epidermidis  alhus 
of  Welch  is  of  low  virulence.  Weichselbaum 
obtained  a  S.  endocardititis  rugatus  from  a  case 
of  endocarditis.  Xot  all  of  these  varieties  produce 
soluble  toxins.  The  pigment  of  S.  aureus  is  an 
excretion  product  which  is  formed  only  in  the 
presence  of  oxygen.  It  is  insoluble  in  water,  sol- 
uble in  alcohol  and  ether,  and  gives  the  reaction 
of  a  lipochrome  (i.  e.,  the  pigment  may  be  saponi- 
fied and  gives  the  lipocyanin  reaction  in  which  the 
pigment  turns  blue  when  treated  with  concentra- 
ted sulphuric  acid). 

Aside  from  wide  individual  variations,  the  re-  Resistance 
sistance  of  staphylococci  to  heat  depends  on  the 
concentration  of  the  suspension,  the  nature  of  the 
medium  (whether  water,  gelatin  or  pus),  and 
whether  the  test  is  a  dry  or  wet  one  (Neisser  and 
Lipstein).  Eighty  degrees  centigrade  for  one-half 
to  one  hour  kills  them  under  all  conditions,  and 
60°  C.  for  one-half  hour  kills  many  strains  when 
suspended  in  bouillon.  They  are  not  killed  by  re- 
peated freezing  and  thawing,  and  are  very  resist- 
ant to  desiccation.  When  in  the  form  of  fine  dust 
they  die  in  twenty-eight  days  (Kirstein).  Resist- 
ance to  the  action  of  sunlight  is  variable;  some 
strains  are  killed  in  from  three  to  five  hours. 


of  Cocci, 


542  IM'ECTION     AND     IMMUNITY. 

Staph3^1ococci  have  fairly  high  resistance  to  anti- 
septics; when  dried,  corrosive  sublimate  (1/1000) 
kills  them  in  two  to  three  hours^  and  when  im- 
bedded in  pus  from  thirteen  to  sixteen  hours  are 
required  (Ottavino).  Meth3^1  alcohol,  tincture  of 
green  soap  and  methyl  violet  are  relatively  good 
disinfectants.  Methyl  violet  in  a  dilution  of 
1/10,000  kills  them  in  from  five  to  fifteen  minutes 
(Stilling).  Formalin  readily  hinders  develop- 
ment, but  its  bactericidal  power  is  low.  It  is 
difficult  or  impossible  to  sterilize  wounds  infected 
with  the  staphylococcus  by  means  of  antiseptics. 

Staphylococci  are  very  widely  distributed  in  na- 
ture and  are  to  be  found  constantly  in  the  super- 
ficial layers  of  the  epidermis  (S.  epidermidis  al- 
hus). 
Leacotactic  In  infcctious  the  staphylococcus  attracts  large 
numbers  of  leucocytes,  and  the  pus  does  not  coagu- 
tances.  \r^^Q^  rpj^^  substaucc  which  attracts  leucocytes  is 
heat-resistant,  since  killed  cultures  will  cause 
abscesses.  In  all  but  the  most  superficial  lesions 
a  characteristic  result  of  infection  is  that  of  cell 
necrosis  and  the  liquefaction  of  tissues.  Neisser 
and  Lipstein  state  that  the  necrotizing  substance 
is  a  soluble  toxin,  since  culture  filtrates  cause 
marked  necrosis  of  the  internal  organs  when  in- 
jected (liver,  heart,  kidney).  "Hence  in  staphylo- 
mycosis we  can  distinguish  two  active  substances 
(v.  Lingelsheim).  the  leucotactic  substance  in  the 
l)odies  of  the  cocci  and  the  more  important  soluble 
staphylotoxin  which  exercises  not  only  a  local  but 
also  a  general  toxic  action  on  the  body'''  (Neisser 
and  Lipstein). 
Amyloid  Davidsou  produccd  amyloid  degeneration  in 
*'^atlon'.  rabbits  and  mice  by  the  injection  of  living  cultures. 


and  Necrotiz 
ing-  Sub 


STAPHYLOCOCCUS     INFECTIONS.  543 

This  was  confirmed  by  Lubarsch,  who  found  the 
condition  most  readily  produced  in  the  chicken 
and  with  more  difficulty  in  the  mouse,  rabbit  and 
dog.  It  rarely  results  if  suppuration  is  avoided. 
Killed  cultures  may  be  used. 

Eabbits  and  mice  are  the  most  susceptible  ani-  suscepti- 
mals.  The  susceptibility  of  man  is  much  greater.  Animaia. 
The  organisms  are  most  virulent  for  rabbits  when 
injected  intravenously,  and  a  variety  of  lesions 
may  result,  as  abscesses  in  various  parts  of  the 
body  (especially  the  kidney,  heart  and  muscles), 
arthritis,  endocarditis,  etc.  They  are  less  patho- 
genic wnen  injected  into  the  pleural  or  peritoneal 
cavities.  Eabbits  are  rarely  to  be  infected  by  the 
feeding  of  cultures.  In  experimental  infections 
degenerations  of  the  axis  cylinders  in  the  white 
and  gi-ay  matter,  and  of  ganglionic  cells,  have  been 
noted.  The  virulence  of  staphylococci  is  subject 
to  great  variations,  and  it  may  be  increased  by 
passage.  In  passing  a  culture  through  the  rabbit 
eight  times,  v.  Lingelsheim  reduced  the  fatal  dose 
for  rabbits  from  5  c.c.  of  a  24-hour  broth  culture, 
to  1/100  c.c,  but  a  corresponding  increase  in  viru- 
lence for  the  mouse  and  guinea-pig  did  not  occur. 
Virulence  for  animals  is  not  a  reliable  index  of 
virulence  for  man. 

The  staphjdococcus  is  the  most  common  pus  infections 
producer  in  man.  The  most  frequent  infections 
are  those  of  the  skin,  the  organisms  gaining  en- 
trance through  the  hair  follicles  rather  than 
through  the  sweat  ducts  (Unna),  resulting  in  such 
conditions  as  acne  pustules,  abscess  of  the  skin 
and  subcutaneous  tissue,  furuncles  and  carbun-  sfcin. 
cles.  They  are  found  almost  constantly  in  the 
lesions  of  impetigo  and  often  in  pure  culture. 
Thev   have   been    much    vaunted    as    a    cause    of 


544  INFECTION     AND     IMMUNITY. 

eczema  and  they  may  be  important  as  a  secondary 
agent  in  this  condition.  The  ordinary  eczema  prob- 
ably is  not  parasitic  in  its  cause,  however  (Sabou- 
raud),  and  Neisser  and  Lipstein  dispute  the  claim 
of  Bender  and  others  that  eczema  produced  by 
staphylococcus  filtrates  is  due  to  products  of  the 
microbe.  This  conclusion  was  justified,  since  the 
same  results  were  obtained  with  pure  bouillon  of 
similar  alkalinity,  the  property  could  not  be  de- 
stroyed by  heat,  and  antistaphylococcus  serum  was 
not  able  to  prevent  the  dermatitis.  Furuncles  may 
be  produced  by  rubbing  virulent  cultures  into  the 
skin,  and  abscesses  by  the  injection  of  minute 
Mncons  amouuts.  The  staph3dococcus  causes  purulent  or 
seropurulent  conjunctivitis  rather  infrequently. 
Primary  infections  of  cavities  which  communicate 
with  the  surface,  as  the  antrum  of  Highmore,  the 
middle  ear,  nose,  bronchi,  lungs  and  tuberculous 
cavities,  are  not  uncommon,  and  mixed  infections 
with  the  staphylococcus  in  these  localities  is  the 
rule,  regardless  of  the  primary  cause.  Infection 
of  the  mucous  surfaces  is  less  common  than  of  the 
skin,  however.  It  rarely  causes  aphthous  inflam- 
mations, anginas,  pneumonia,  enteritis  and  cys- 
titis when  unmixed  with  other  organisms. 

Septicemia.  Staphylococcus  septicemia  of  great  virulence  oc- 
casionally follows  primary  infection  in  other  parts 
of  the  body,  as  wound  infections,  tonsillitis,  puer- 
peral infection  (rare)  and  the  so-called  malignant 
carbuncles  of  the  upper  lip.  In  such  instances  a 
thrombophlebitis  may  be  the  means  by  which  the 
organisms  are  poured  into  the  circulation  in  large 

Serous  snr-   numbcrs.     Inflammations  of  the  serous  surfaces, 

facen  and  hi  •,  -■  -■  -!• 

Bones,  as  the  pleura,  peritoneum  and  endocardium,  are 
rarely  primary,  but  follow  systemic  infection;  the 


IMMUNITY     TO     STAPHYLOCOCCUS.         545 

endocarditis  usually  is  ulcerative  and  leads  to 
metastatic  foci  of  infection.  Staphylococci  have  a 
particular  affinity  for  the  bony  tissues,  especially 
the  bone  marrow  and  the  periosteum;  they  are  the 
most  common  agent  in  the  production  of  osteomye- 
litis and  cause  the  so-called  periostitis  albuminosa. 
It  is  thought  that  they  may  persist  in  bone  lesions 
for  a  period  of  years  and  later  start  up  a  fresh 
process.  They  involve  the  joints  less  frequently, 
but  have  been  found,  presumably  as  secondary 
agents,  in  acute  rheumatism,  and  as  the  primary 
cause  in  pyemic  abscesses  of  the  joints.  They  are 
found  occasionally  in  abscesses  of  the  mammary 
and  parotid  glands,  liver,  lungs,  and  in  pyorrhea  Mixed  ^ 
alveolaris  (rare).  The  cultivation  of  staphylococci 
in  a  pure  state  from  the  tissues  does  not  of  neces- 
sity indicate  that  they  are  the  essential  organism 
in  the  process  (smallpox,  rheumatism,  etc.).  Pre- 
vious infections  by  many  organisms,  and  likewise 
traumas,  predispose  to  localization  of  the  staphy- 
lococcus, and  any  infectious  process  in  the  skin  is 
likely  to  be  invaded  by  these  organisms  secondarily. 

Infections  with  the  staphylococcus  are  charac-  Leucocytes 

ill.  ^Vs-tmrfl/X 

terized  by  both  local  and  general  leucocytosis,  the  immnnity. 
local  leucocytosis  being  a  part  of  the  suppurative 
process.  As  stated  above,  the  staphylococcus  con- 
tains a  thermostabile  constituent,  which  exerts  a 
positive  chemotatic  effect  on  the  leucocytes.  Al- 
though it  is  possible  to  consider  the  accumulation 
of  the  leucocytes  merely  as  the  expression  of  this 
affinity,  it  has  been  shown  with  sufficient  clearness 
that  polymorphonuclear  leucocytes  are  able  to  in- 
gest living   staphylococci   and   kill  them.^      They 

3.  Phagocytosis    of   staphylococci    was    first   observed    by 
Kirch   in   1889. 


54(i  INFECTION     AND     IMMUNITY. 

may  be  found  within  the  leucocytes  in  both  natural 
and  experimental  infections.  When  injected  into 
the  pleural  or  peritoneal  cavity  of  the  guinea-pig 
phagocytosis  is  well  begun  within  one-half  hour 
and  reaches  its  height  in  four  to  five  hours. 
Bactericidal       Experiments  which  were  begun  by  van  der  Velde 

cocytes  and  in  1894  demonstrate  the  bactericidal  action  of  leu- 
Exuda^es!  cocytic  exudatcs.  The  action  is  not  so  strorg  in 
the  cell-free  exudate  as  when  the  leucocytes  are 
present,  and  when  the  leucocytes  are  caused  to  dis- 
integrate by  some  means,  as  by  alternate  freezing 
and  thawing,  trituration,  the  action  of  leucocidin, 
or  treatment  with  distilled  water,  the  bactericidal 
power  of  the  fluid  is  increased.  Presumably  the 
leucocytes  discharge  their  bactericidal  contents  into 
the  surrounding  fluid  as  a  result  of  such  inju- 
ries. The  nature  of  the  bactericidal  substance  is 
not  known  exactly;  from  the  fact,  however,  that 
leucocytes  contain  complement  it  has  been  suggest- 
ed that  they  discharge  this  complement  which  then 
acts  with  amboceptors  in  the  serum  in  destroying 
the  organisms.  It  is  possible  that  the  cocci  before 
they  are  taken  up  by  the  leucocytes  have  absorbed 
amboceptors  and  after  their  ingestion  are  suscepti- 
ble to  the  action  of  the  endocellular  complement. 
In  contrast  to  the  distinct  bactericidal  power  of  the 
leucocytes  stands  the  very  low  or  entire  absence  of 
a  similar  action  by  both  normal  and  immune 
serums.  It  would  seem,  then,  that  the  most  power- 
ful agency  in  natural  resistance  to  invasion  by  the 
staphylococcus  is  represented  in  the  phagocytic 
and  bactericidal  activities  of  the  leucocytes.  Opso- 
nins are  essential  for  phagocytosis. 
Active-iin-       In  1888,  Richct  and  Hericourt  showed  that  it 

mnnization.  ^^^^^  possible  to  iucrcase  the  resistance  of  the  rabbit 


IMMUNIZATION.  547 

against  the  staphylococcus  by  immunization  with 
pure  cultures.* 

One  may  immunize  either  with  living  or  killed 
cultures  or  with  culture  filtrates.  Immunization 
with  the  bacterial  cells  must  proceed  slowly  in 
order  to  avoid  killing  the  animals.  When  filtrates 
containing  leucocidin  or  staphylolysin  (hemolysin) 
are  used,  antitoxins  for  these  substances  are 
formed.  The  antistaphylolysin  obtained  for  one 
strain  neutralizes  the  hemolysin  of  all  strains. 
The  most  prolonged  immunization  with  bacterial 
cells  causes  no  appreciable  increase  in  bacterioly- 
sins. 

The  serum  of  one  who  has  recovered  from  a  Protection 
staphylococcus  infection,  or  that  of  immunized  an-  semms. 
imals,  is  protective  for  other  animals;  0.1  to  0.2 
c.c.  of  an  immune  serum  given  subcutaneously 
protected  mice  from  a  fatal  dose  of  cocci  given 
two  hours  later,  whereas  other  mice  were  killed  in 
from  8  to  12  hours.  When  the  serum  was  given 
24  hours  in  advance  of  the  culture,  from  0.02  to 
0.03  c.c.  saved  them  (v.  Lingelsheim,  cited  by 
Neisser).  The  results  of  Petersen  and  of  Proscher 
were  similar.  In  spite  of  this  rather  strong  pro- 
tective action,  immune  serums  have  little  or  no 
curative  power. 

N'o  clearer  explanation  of  the  action  of  the  im-  Properties 

rt.       T     T     1         XT         ***  Serums. 

mune  serum  is  given  than  that  afforded  by  the 
experiments  of  Proscher,  who  injected  guinea- 
pigs,  rabbits  and  mice  with  normal  and  immune 
serums  and  followed  this  24  hours  later  with  in- 
oculation of  the  cocci  into  the  peritoneal  cavity. 


4.  Their  experiments  in  protecting  and  curing  other  ani- 
mals with  antistaphylococcus  serum  represent  the  first  at- 
tempt made  In  the  direction  of  passive  Immunization. 


548  INFECTION     AND     IMMUNITY. 

Thirty  minutes  after  injection  of  the  cocci  the 
exudate  in  all  animals  showed  an  enormous  leuco- 
cytosis.  At  first  they  were  chiefly  mononuclears, 
but  later  gave  place  to  polynuclears.  In  the  ani- 
mals which  had  received  the  immune  serum,  mas- 
sive phagocytosis  had  occurred,  and  in  the  course 
of  an  hour  very  few  cocci  were  extracellular.  On 
the  other  hand,  practically  no  phagocytosis  had 
taken  place  in  the  animals  which  had  received  the 
normal  serum  (cited  by  Neisser).  Virulent 
staphylococci  were  taken  up  less  readily  than 
avirulent.  Such  results  suggest  that  the  protective 
power  of  the  serum  is  due  to  its  ability  to  stimulate 
phagocytosis,  and  this  in  turn  depends  on  the 
increased  quantity  of  bacteriotropic  substances 
formed  in  the  serum  as  the  result  of  immunization 
(Wright  and  others). 
Vaccination.  In  the  hands  of  Wright,  vaccination  with  killed 
cultures  of  the  staphylococcus  has  been  very  suc- 
cessful in  the  cure  of  obstinate  cases  of  acne,  fu- 
runculosis  and  many  other  chronic  staphylococcus 
infections.  Bouillon  cultures  are  grown  for  three 
weeks  and  then  killed  by  exposure  to  a  tempera- 
ture of  60°  C.  for  an  hour.  In  order  to  control 
dosage,  the  vaccine  is  standardized  by  estimating 
the  number  of  bacilli  in  each  cubic  centimeter. 
This  is  done  by  mixing  equal  quantities  of  the 
vaccine  with  normal  blood,  and,  after  staining  a 
preparation  on  a  slide,  determining  the  ratio  of 
cocci  to  erythrocytes.  There  being  about  5,000.000 
erythrocytes  to  the  cubic  millimeter  in  normal 
blood,  the  number  of  cocci  is  readily  reckoned 
from  the  ratio  which  was  found.  From  2,500 
millions  to  7,500  millions  of  cocci  may  be  given 
in    an    injection.      The    quantity    to    be   used    is 


OPSONIC     INDEX. 


549 


determined  by  the  effect  which  an  injection  has  on 
the  opsonic  content  of  the  patient's  serum.  If  a 
suitable  dose  has  been  given,  there  occurs  a  short 
negative  phase  in  which  the  opsonins  are  decreased 
in  quantity,  and  this  is  followed  by  a  rather  pro- 
longed positive  phase  when  they  undergo  an  in- 
crease. If  too  large  a  dose  is  given,  the  negative 
phase  is  exaggerated  and  prolonged.  In  many  in- 
stances it  has  been  noted  that  improvement  and 
recovery  go  hand  in  hand  with  an  increase  in  the  "Opsonic 
opsonins.  As  in  streptococcus  infections  the  total 
resisting  power  of  the  body  depends  on  the  varia- 
tion in  the  capability  of  the  leucocytes  to  take  up 
and  digest  cocci  as  well  as  the  opsonic  action  of 
the  serum. 

The  normal  serums  of  man  and  many  animals  ^fg^^**" 
may  agglutinate  the  staphylococcus,  but  with  no 
constancy.  In  one  instance  human  serum  aggluti- 
nated in  a  dilution  of  1-100  (Kraus  and  Low), 
and  normal  sfoat  serimi  in  a  dilution  of  from 
1-50  to  1-400  (Amberger,  cited  by  Neisser).  The 
serums  from  cases  of  staphylococcus  infection 
(e.  g.,  osteomyelitis)  and  of  highly  immunized  an- 
imals undergo  an  increase  in  the  quantity  of  ag- 
glutinins. The  agglutination  usually  is  strongest 
for  the  homologous  strain,  and  if  other  strains  are 
agglutinated  equally  it  signifies  a  close  relation- 
ship to  the  homologous  strain. 

From  the  fact  that  only  pathogenic  strains  pro- 
duce hemolysin  and  leucocidin,  Neisser  and 
Wechsberg  considered  them  specifically  different 
from  non-pathogenic  strains.  This  view  is  borne 
out  by  the  results  obtained  with  the  agglutination 
test.  Serums  obtained  by  immunization  with 
pathogenic  strains  have  a  much  higher  aggluti- 


550  INFECTION     AND     IMMUNITY. 

nating  power  for  these  strains  than  for  non-patho- 
genic varieties,  and  the  converse  is  also  true.  There 
are,  however,  many  variations  in  the  agglutinabil- 
ity  of  the  members  in  each  group,  a  fact  which  in- 
dicates variations  in  the  receptor  complex  of  the 
different  strains.  It  has  been  suggested  that  a 
polyvalent  serum  obtained  by  immunization  with 
a  sufficient  variety  of  pathogenic  strains  will  be 
efficient  in  differentiating  the  latter  from  non- 
pathogenic varieties  by  means  of  the  agglutina- 
tion test. 

Wright,  noting  an  increase  in  the  agglutinating 
power  when  patients  are  treated  by  his  method, 
considers  that  this  increase  is  an  index  of  the  im- 
jnunity  which  is  established. 

IV.    MICROCOCCUS    CATARRHALIS. 

For  some  years  diplococci  resembling  the  gono- 
coccus  and  the  meningococcus  morphologically  and 
in  staining  reactions  have  been  found  in  the  spu- 
tum by  a  number  of  observers,  and  to  this  coccus 
Pfeiffer  gave  the  name  of  Micrococcus  catarrhalis. 
It  is  frequently  found  in  the  respiratory  passages 
in  influenza-like  infections  and  other  inflamma- 
tory conditions,  and  occasionally  in  lobular  pneu- 
moniu.  It  may  be  associated  with  the  influenza 
bacillus  or  the  pneumococcus.  Among  140  cases 
of  diseases  of  the  respiratory  passages  Ghon  and  H. 
Pfeiffer  found  it  81  times,  and  M.  Neisser  demon- 
strated it  in  16  cases  of  whooping-cough,  in 
one  of  measles  and  scarlet  fever,  and  in 
two  of  diphtheria.  It  loses  significance  in  relation 
to  these  diseases,  however,  since  Jiindell  found  it 
frequently  in  the  mucus  of  the  normal  trachea, 
and  Welch selbaum  cultivated  it  frequently  from 


GOKOCOCCUS.  551 

the  healthy  nasal  fossa?.  According  to  Ghon, 
Pfeiffer  and  Sederl,  ''Micrococcus  catarrlialis, 
without  the  association  of  other  microbes,  is  able 
to  cause  bronchitis  and  pneumonia  with  the  clini- 
cal type  of  pneumonia  due  to  the  pneumococcus. 
The  symptoms  caused  by  the  Micrococcus  catarrli- 
alis do  not  form  a  clinical  type.  They  resemble 
infections  by  the  pneumococcus  or  the  bacillus  of 
Pfeiffer  (Influenza)  ^^  (cited  by  Bezancon  and  de 
Jong).  Others  are  not  so  positive  concerning  the 
pathogenic  properties  of  the  organism.  Its  etio- 
logic  role  is  not  yet  well  established.  It  has  little 
pathogenicity  for  animals,  although  peritoneal  and 
pleural  infection  is  possible  in  guinea-pigs. 

It  differs  from  the  gonococcus  and  meningococ- 
cus in  certain  cultural  characters. 

V.    GONORRHEA  AND  OTHER  INFECTIONS   WITH   THE 
GONOCOCCUS. 

A.  N'eisser  discovered  the  gonococcus  in  1879,  The  Gono- 
cultivated  it  in  1884,  and  demonstrated  its  specific 
relation  to  gonorrhea  by  the  inoculation  of  pure 
cultures  into  the  human  urethra.  It  is  a  diplo- 
coccus,  young  pairs  having  a  figure-of-eight  con- 
tour, whereas  older  pairs  show  a  typical  biscuit 
or  coffee-bean  shape.  The  organism  is  non-motile, 
has  no  flagella  and  forms  no  spores.  It  can  be 
cultivated  only  on  media  which  contain  serum, 
ascitic  or  a  similar  fiuid.  Its  failure  to  stain  by 
Gram's  method  is  of  great  diagnostic  importance 
in  the  examination  of  urethral  discharges;  other 
organisms  resembling  the  gonococcus  are  found  in 
the  urethra  and  vagina  with  great  rarity.  The 
reaction  loses  its  differential  value  in  the  examina- 
tion of  secretions  of  the  nose,  mouth,  and,  to  some 


coccus. 


552 


INFECTION     AND     IMMUNITY. 


Cnltivation 

and  Resist- 

aace. 


extent,  of  the  conjunctiva,  where  the  meningococ- 
cus and  the  Micrococcus  catarrhalis  may  be  en- 
countered. 
Phagocytosis.  In  the  purulcut  stage  of  a  gonorrheal  infection 
the  cocci  are  found  almost  entirely  within  the  leu- 
cocytes, whereas  in  earlier  stages,  when  the  dis- 
charge is  slight  and  of  a  mucous  character,  and 
also  during  convalescence,  when  the  secretion 
again  becomes  mucous,  they  are  largely  extracel- 
lular. They  are  never  within  the  nuclei.  The 
process  is  one  of  active  phagocytosis  in  which  the 
cocci  play  a  passive  role.  They  occur  not  only  on 
the  surface  of  the  epithelium,  but  penetrate  be- 
tween and  beneath  the  epithelial  cells,  and  even 
into  the  adjacent  connective  tissue. 

In  culture  media  growth  is  slow  and  scant,  and 
cultures  rarely  live  longer  than  one  or  two  weeks, 
unless  they  are  transplanted  to  suitable  fresh  media. 
On  the  latter  they  may  be  carried  through  many 
generations  without  losing  their  virulence.  When 
dried  they  die  very  quickly,  but  may  live  for  some 
hours  on  linen  (towels)  or  the  skin,  and  for 
twenty-four  hours  in  warm  water.  They  are  very 
susceptible  to  temperatures  above  42°  or  43°  C. 
and  show  very  little  resistance  to  antiseptics,  par- 
ticularly the  silver  salts. 

The  gonococcus  secretes  no  soluble  toxin,  but 
contains  an  endotoxin  or  toxic  "protein'^  which 
causes  local  and  general  symptoms  in  both  man 
and  animals.  Dead  cultures  produce  an  inflamma- 
tory exudate  in  the  peritoneal  cavity  of  guinea- 
pigs  and  mice,  resulting  in  death  if  the  dose  is 
sufficiently  large,  and  when  injected  into  the 
urethra  of  man  a  temporary  inflammation  results. 
An  actual  infection  of  any  sort  can  not  be  pro- 


Toxicity  and 
Virulence. 


GONOCOCCUS.  553 

duced  in  animals;  the  cocci  are  killed  without  be- 
ing permitted  to  ^proliferate.  The  endotoxin  (gon- 
otoxin)  is  fairly  resistant  to  heat,  being  destroyed 
only  after  prolonged  exposure  to  a  temperature  of 
100°  C. 

In  man  the  mucous  membranes  and  endothelial  T^Jsues.*^*'* 
surfaces  are  more  susceptible  to  infection  than 
other  tissues.  The  urethra  of  male  and  female  at 
all  ages,  the  conjunctiva  in  the  new-born,  the 
vagina,  uterus  and  tubes  are  probably  the  most 
susceptible.  Less  susceptible  are  the  vagina  in 
older  women,  especially  those  who  have  borne  chil- 
dren, the  bladder  and,  in  adults,  tlie  conjunctiva. 
It  is  remarkable  that  there  are  so  few  cases  of 
gonorrheal  ophthalmia  in  adults,  considering  the 
opportunities  for  infection.  Infection  of  the 
mouth,  nose  and  tear  sacs  is  extremely  rare.  Ex- 
tension from  the  urethra  to  adjacent  structures 
takes  place  either  by  way  of  the  surfaces,  as  in 
involvement  of  the  prostate,  epididymis,  glands  of 
Bartholin,  uterus,  tubes,  ovaries,  peritoneum,  blad- 
der and  kidneys,  or  by  way  of  the  lymphatics  as  in 
infections  of  the  periurethral  tissue  or  cellular  tis- 
sue of  the  pelvis.  Usually  infections  of  the  bladder 
and  kidney,  and  not  infrequently  of  the  prostate, 
Fallopian  tubes  and  pelvic  tissue  are  of  a  mixed 
character  (staphylococcus,  streptococcus),  but  not 
necessarily  so.  Arthritis,  tendovaginitis,  endocar- 
ditis, which  usually  is  vegetative  but  may  be  ulcer- 
ative, are  the  more  common  metastatic  complica- 
tions. Less  frequent  are  pericarditis,  pleuritis, 
subcutaneous  abscesses  and  iritis.  As  to  whether 
the  cutaneous  phenomena  sometimes  seen  are  due 
to  metastases  or  are  of  purely  toxic  origin  seems  to 
be  undetermined.     The  blood  stream  mav  be  in- 


554  INFECTION     AND     IMMUNITY. 

fected  by  way  of  the  lymphatics  or  local  blood 
vessels  (gonorrheal  thrombosis). 

The  influence  of  the  enormous  phagocytosis  of 
the  cocci  on  the  course  of  gonorrhea  is  unknown. 
Since  the  ingested  cocci  usually  have  a  typical 
form  and  stain  well,  it  would  seem  that  they  resist 
the  action  of  the  leucocytic  ferments.  Likewise 
the  nuclei  of  the  leucocytes  usually  stain  well, 
hence  there  is  no  evidence  of  a  marked  toxicity 
of  the  cocci  for  these  cells.  The  mechanical  im- 
prisonment of  the  organisms  by  the  leucocytes 
may  be  of  influence  in  localizing  the  infection. 

Urethral  Duriug  the  coursc  of  gonorrhea  "there  takes 
place  a  pronounced  metaplasia  of  the  epithelium 
in  which  the  cylindrical  cells  are  changed  into  a 
more  cuboidal  and  even  pavement  form.'^  Follow- 
ing this  change  the  gonococci  are  limited  to  the 
surface  of  the  altered  epithelium  and  penetrate 
more  deeply  only  in  the  vicinity  of  the  glands  and 
crypts.  "Eventually  the  gonorrheal  process  is 
limited  to  such  isolaled  points  and  the  gonorrhea 
thereby  enters  into  a  chronic  stage"  (observations 
of  Finger^  cited  by  Neisser  and  Scholtz). 

Chronic  The  couditious  which  cause  the  subsidence  of 
acute  gonorrhea  and  allow  it  to  persist  as  a  chronic 
infection  have  been  the  subject  of  much  specula- 
tion, unproductive  for  the  most  part.  It  is  not 
due  to  a  decrease  in  the  virulence  of  the  cocci 
since  their  original  infectiousness  is  retained  for 
others ;  nor  does  the  local  resistance  of  the  mucous 
membrane  reach  a  high  point,  since  reinfection, 
or  better  "superinfection"  is  possible  at  any  time. 
A  man  suffering  from  chronic  gonorrhea  and 
having  infected  his  wife,  may  again  be  infected 
by  hi?  wife  when  the  gonorrhea  of  the  latter  has 


Gonorrhea. 


GONOCOCCUS     SERUM.  555 

become  subacute  or  chronic.  It  has  been  suggested 
that  the  condition  in  chronic  gonorrhea  may  be 
one  of  "mutual  habituation  between  the  mucous 
membrane  and  the  gonococcus/'  i.  e.,  a  habituation 
between  this  particular  mucous  membrane  and 
this  particular  gonococcus.  Because  of  prolonged 
existence  under  unvarying  conditions,  the  growth 
energy  of  the  organism  may  have  become  less, 
whereas,  if  it  is  placed  in  a  slightly  different  me- 
dium (transference  to  another  individual),  its 
growth  energy  (ability  to  proliferate),  becomes 
augmented,  and  reinfection  of  the  original  host 
with  the  same  strain  becomes  possible. 

It  has  often  been  noted  that  subsequent  attacks 
run  a  milder  course  than  the  primary  infection, 
but  susceptibility  is  always  present. 

Mendez,  Calvino,  and  also  de  Christmas  have  immunity. 
immunized  with  the  coccus  or  toxic  substances 
prepared  from  it.  By  growing  the  organism  in 
serum  bouillon  de  Christmas  prepared  a  toxin, 
the  toxicity  of  which  was  tested  by  intracerebral 
injections  in  the  guinea-pig.  Im^munization  of 
the  guinea-pig  resulted  in  a  serum  with  antitoxic 
properties.  Corroborative  work  has  not  been  pub- 
properties.  Torrey  has  shown  that  by  immuniza- 
tion of  animals  a  serum  may  readily  be  produced 
which  contains  specific  bacteriolysins,  agglutinins, 
precipitins  and  complement  deviation  antibodies. 
Hamilton  and  others  have  found  that  in  gonor- 
rheal vulvovaginitis  the  opsonic  index  is  low  in 
early  stages  and  in  those  in  which  recovery  does 
not  take  place,  and  becomes  higher  with  recovery. 

Torrey    in    1906    prepared    an    antisronococcus  serotiierapy 

/        .  .        .  „         ,  ,  .  £.  and  Vacci- 

serum    by  immunization   of   rabbits.      Since   that  nation. 
time,  a  number  of  different  serums  have  been  pre- 


55G  INFECTION     AND     IMMUNITY. 

pared  from  such  animals  as  horses  and  rams.  The 
reports  concerning  the  value  of  antigonococcus 
serum  have  been  as  yet  too  varied  to  admit  of  a 
conclusion. 

The  subcutaneous  injection  of  dead  gonococci 
for  curative  purposes  has  been  apparently  of  little 
value  in  acute  urethral  infections.  In  chronic 
infections  of  the  urethra,  prostate  and  seminal  vesi- 
cles some  satisfactory  results  have  been  obtained. 
Cole  and  Meakins,  and  Irons  find  that  the  vaccine 
treatment  of  gonorrheal  arthritis  is  of  value  in 
lessening  the  pain  and  in  shortening  the  course  of 
the  infection. 

VI.    EPIDEMIC     CEREBROSPINAL    MENINGITIS. 

Microbes  Acutc  inflammation  of  the  meninges  may  be 
Meningitis,  causcd  by  a  number  of  micro-organisms:  Micro- 
coccus meningitidis,  also  called  the  Diplococcus 
intracellularis  meningitidis,  or  briefly  the  men- 
ingococcus; Diplococcus  pneumonice;  Streptococ- 
cus pyogenes;  Staphylococcus  pyogenes;  Bacillus 
influenzcB;  Bacillus  pneumonice;  Bacillus  typlio- 
sus;  Bacillus  coli  communis;  Bacillus  mallei;  Ba- 
cillus pestis.  The  first  two  of  this  number,  the 
meningococcus  and  the  pneumococcus,  in  addition 
to  causing  sporadic  cases,  also  produce  more  or 
less  extensive  epidemics  of  so-called  primary  men- 
ingitis. That  the  pneumococcus  may  also  cause 
meningitis  secondary  to  pneumococcus  infections 
in  other  parts  of  the  body  has  been  mentioned. 
Also  the  meningitis  caused  by  the  other  pyogenic 
cocci  usually  is  secondary  to  some  other  suppura- 
tive focus,  often  the  middle  ear;  that  caused  by 
the  organisms  of  typhoid,  glanders,   plague   and 


MENINGOCOCCUS.  557 

influenza  occurs  during  the  course  of  the  diseases 
caused  by  the  corresponding  micro-organisms. 

Previous  to  1887  diplococci  resembling  the  pneu-  Micrococcns 
mococcus  had  been  found  m  the  exudate  m  cases 
of  cerebrospinal  meningitis  by  Foa  and  Bordoni- 
Uffreduzzi,  by  Fraenkel  and  others.  Weichsel- 
baum  made  similar  observations  during  the  same 
year,  and  in  addition  described  six  cases  in  which 
a  diplococcus  of  another  nature  was  present  in 
pure  cultures.  To  the  latter  he  gave  the  name  of 
Diplococcus  intracellularis  meningitidis.  Exten- 
sive observations  by  others,  both  in  Europe  and 
America  (Councilman,  Mallory  and  Wright,  and 
others),  revealed  the  presence  of  the  last-named 
organism  in  many  instances,  and  showed  that  it  is 
the  most  common  cause  of  epidemic  cerebrospinal 
meningitis. 

The  meningococcus  resembles  the  gonococcus 
closely  in  that  it  is  usually  found  in  biscuit-shaped 
pairs,  nearly  always  within  pus  cells,  and  does  not 
stain  by  Gram's  method  (Weichselbaum).  It  is 
properly  to  be  called  a  micrococcus  since  it  divides 
in  two  transverse  directions  (Albrecht  and  Ghon)  ; 
tetrads,  small  groups  and  short  chains  are  some- 
times seen.  However,  it  forms  no  striking  chains, 
is  non-motile  and  produces  no  spores.  Growth 
may  be  obtained  on  some  of  the  ordinary  media 
(glycerin  agar),  in  which  the  organism  dijffers 
from  the  gonococcus,  but  a  medium  which  contains 
blood  or  serum  is  much  more  favorable.  It  is  an 
obligate  aerobe,  grows  best  at  the  body  tempera- 
ture and  Virulence  is  soon  lost  under  artificial 
conditions. 

It  produces  a  membrane  on  meat  broth  with  viability. 
clouding   of  the  medium.     Viability   is   retained 


558 


INFECTION     AND     IMMUNITY. 


Virulence; 
Endotoxin. 


Infection 
Atria. 


only  for  a  few  days  at  room  temperature.  When 
dried  on  paper  and  exposed  to  the  sunlight  it  lives 
no  longer  than  twenty-four  hours,  in  a  dark  room 
seventy-two  hours  (Councilman,  Mallory  and 
Wright).  It  is  killed  by  a  temperature  of  65°  C. 
for  thirty  minutes   (Albrecht  and  Ghon). 

The  meningococcus  has  little  virulence  for  ani- 
mals. When  injected  in  sufficient  quantity  into 
the  peritoneal  or  pleural  cavity  of  white  mice 
death  results  in  from  twenty-four  to  forty-eight 
hours,  but  not  when  given  subcutaneously.  Men- 
ingitis may  be  produced  by  subdural  injections, 
but  the  disease  does  not  resemble  the  epidemic 
meningitis  of  man.  So  far  as  is  known  at  present 
the  organism  does  not  produce  a  soluble  toxin,  but 
possesses  rather  an  endotoxin.  Although  the  dis- 
ease is  usually  spoken  of  as  a  primary  meningitis, 
there  is  reason  to  believe  that  it  is  secondary  to  an 
acute  rhinitis  or  acute  inflammation  of  the  acces- 
sory sinuses  or  middle  ear,  in  many  instances. 
From  these  places  the  coccus  may  readily  reach  the 
meninges  by  way  of  the  lymphatic  channels,  or 
blood.  The  latter,  according  to  Elser  and  Hun- 
toon,  is  probably  the  usual  route.  It  has  been 
found  repeatedly  in  the  noses  of  those  associated 
with  patients  with  the  disease;  in  such  cases  an 
acute  rhinitis  may  be  present  without  the  subse- 
quent development  of  meningitis.  The  clinical  his- 
tory shows  that  the  infection  commonly  is  preceded 
by  acute  rhinitis.  The  inflammation  in  the  menin- 
ges is  always  cerebrospinal  in  its  distribution  and 
is  characterized  by  a  purulent  or  fibrino-purulent 
exudate  in  which  the  diplococci  are  present  in 
varying  quantities.  Diagnosis  may  often  be  estab- 
lished  clinically   by   the   microscopic   or   cultural 


MENINGITIS. 


559 


examination  of  the   cerebrospinal   fluid  which  is 
removed  by  lumbar  puncture. 

Acute  encephalitis,  acute  bronchitis,  lobar  pneu-  ^i^^J  ^nd" 
monia  and  acute  arthritis  have  been  observed  as  J^ther^ 
complications,  in  which  organisms  resembling  the 
meningococcus  have  been  found  in  a  number  of 
instances.  An  accompanying  bronchitis,  lobar  or 
lobular  pneumonia  may  be  caused  by  mixed  infec- 
tion with  other  organisms  (pneumococcus,  strepto- 
coccus, staphylococcus).  Since  it  would  be  diffi- 
cult to  explain  some  of  these  complications  except 
on  the  basis  of  metastasis,  it  seems  very  probable 
that  the  organism  reaches  the  blood  stream.  Micro- 
cocci resembling  the  meningococcus  have  been 
found  in  acute  bronchitis,  rhinitis,  lobular  pneu- 
monia and  conjunctivitis,  in  the  absence  of  cere- 
bral involvement,  and  it  is  possible  that  it  may  be 
the  cause  of  independent  inflammations  in  these 
tissues.  Weichselbaum,  however,  is  inclined  to 
doubt  the  identity  of  such  organisms  with  the 
meningococcus.  Particularly  in  cases  of  bronchi- 
tis and  lobular  pneumonia  the  coccus  may  be  con- 
fused with  the  Micrococcus  catarrlialis  of  Pfeiffer, 
with  which  it  is  identical  morphologically. 

The  extent  to  which  the  meningococcus  is  a 
normal  inhabitant  of  the  nasal  mucous  membrane 
is  unknown. 

Since  the  organism  seems  to  be  excreted  chiefly 
or  only  with  the  nasal  discharges,  the  latter  prob- 
ably are  important  for  transmission  of  the  infec- 
tion. Because  of  the  low  resistance  of  the  organ- 
ism to  desiccation  and  light,  transmission  prob- 
ably is  a  fairly  direct  one.  This  is  suggested  also 
by  the  occasional  occurrence  of  epidemics  in  insti- 
tutions.   Contagiousness  is  of  a  rather  low  order; 


Transmission 
anri  Con- 
tag'ionsness. 


560  INFECTION     AND     IMMUNITY. 

this  is  indicated  by  the  distribution  of  the  111 
cases  observed  by  Councihnan,  Mallory  and 
Wright  in  Boston,  the  city  being  somewhat  dif- 
fusely infected  with  very  little  tendency  of  the  dis- 
ease to  occur  in  groups  of  individuals  or  in  several 
members  of  a  family. 

The  desirability  of  avoiding  contact  with  the 
infected  is  evident;  special  prophylactic  meas- 
ures are  not  known.  In  the  presence  of  an  epi- 
demic the  treatment  of  rhinitis  with  local  antisep- 
tics would  suggest  itself. 
snscepti-  Children  and  young  people  are  particularly  sus- 
immanity.  ccptible  to  both  epidemic  and  sporadic  infections 
with  the  meningococcus.  Exposure  incident  to  the 
cold  and  variable  weather  of  the  winter  and  spring, 
in  which  seasons  the  disease  prevails,  may  be  in- 
fluential in  lowering  resistance.  Second  attacks 
are  rare,  Councilman,  Mallory  and  Wright  col- 
lecting only  five  such  examples  from  the  literature. 
Lipierre  immunized  animals  with  culturps  anri 
with  a  toxin,  the  latter  being  a  glycerin  extract  of 
old  cultures.  Their  resistance  to  infection  was 
said  to  be  increased,  and  the  serum  of  highly  im- 
munized animals  was  antitoxic,  preventive  and 
curative  for  other  animals.  Corroborative  work 
is  lacking.  According  to  Davis,  the  serum  in 
cases  of  epidemic  meningitis  shows  an  increased 
bactericidal  power  for  the  coccus  on  the  thirteenth 
day  of  the  disease;  the  agglutinins  which  develop 
probably  persist  for  some  time,  but  are  little  above 
Normal  human  serum  is  distinctly  bactericidal 
toward  the  meningococcus.  This  property  is 
increased  in  sera  of  meningitis  cases,  and  is  dimin- 
ished, but  not  entirely  destroyed,  by  heating  to  60° 
C.  for  thirty  minutes.  Cerebrospinal  fluid  acts  in 
much   the   same   way   as   heated   serum.     Normal 


MENINGITIS     SERUM. 


561 


Sernm 
Therapy. 


cerebrospinal   fluid  does  not  contain  opsonin  for 
meningococci. 

In  1906^  antimeningitis  serum  was  prepared  in 
this  country  by  Flexner  and  in  Germany  by  Kolle 
and  Wassermann  and  Jochmann.  The  report  of 
Kolle  and  Wassermann  was  the  first  to  appear.  It 
was  quickly  followed  by  that  of  Jochmann  and 
later  by  that  of  Flexner. 

Flexner  prepared  his  sermn  as  follows :  Horses 
were  inoculated  siibcutaneonsly  with  one-fourth  of 
a  sheep's  serum  agar  slant  culture  of  meningococci 
which  had  been  killed  by  heating  to  60°  C.  for 
thirty  minutes.  The  dose  was  doubled  at  each 
subsequent  injection  until  an  amount  equal  to 
four  test-tube  growths  could  be  given  at  intervals 
of  from  five  to  seven  days.  Alternate  injections 
of  living  organisms  and  autolyzate  of  organisms 
were  then  given  at  seven-day  intervals^  in  increas- 
ing doses  until  large  quantities  were  given.  The 
serum  prepared  in  this  way  contains  bacteriolytic 
amboceptors,  opsonins^  agglutinins  and  comple- 
ment-fixation antibodies.  It  has  also  an  antitoxic 
action  on  toxic  autol3^zates  of  meningococci. 

Nearly  all  the  above-named  antibodies  have  been  standard 
used  to  estimate  the  therapeutic  value  of  the 
serum.  Jochmann,  and  Kolle  and  Wassermann 
estimated  the  strength  of  antimeningitis  serum  by 
the  protection  afforded  mice  and  guinea-pigs 
asrainst  live  meningococci.  The  method  is  unsatis- 
factory  because  of  the  difference  of  virulence  of 
various  strains  of  meningococci.  Jobling  con- 
cludes that  the  estimation  of  the  dilution  of  the 
serum  at  which  opsonic  action  is  still  present  gives 
the  best  indication  as  to  the  value  of  the  serum. 
"As  a  definite  and  suitable  standard  of  strenoth 


562  INFECTION     AND     IMMUNITY. 

a  minimi-im  dilution  activity  of  a  1  to  5,000  dilu- 
tion of  the  antiserum  is  proposed." 
Action  and       Flexnei'  and  Joblinsr  conclude  from  a  study  of 

Uses  of  tne  .  .  ^  -^ 

sernm.  the  spmal  fluid,  that  the  most  important  action 
of  the  serum  depends  on  bacterioh^sis  and 
increased  phagocytic  action.  They  give  the  follow- 
ing instructions  for  the  use  of  the  serum  :^ 

^'^The  antiserum  should  be  kept  in  a  refrigerator 
until  it  is  to  be  used,  when  it  should  be  warmed 
to  the  body  temperature  before  it  U  injected. 

"The  antiserum  is  to  be  introduced  directly  into 
the  spinal  canal  after  the  withdrawal  of  cerebro- 
spinal fluid  by  means  of  lumbar  puncture. 

"The  quantity  of  antiserum  to  be  used  at  a  sin- 
gle injection  should  not  exceed  for  the  present 
30  c.c.  It  is  desirable,  although  it  would  not 
appear  essential,  to  withdraw  from  the  spinal  canal 
at  least  as  much  fluid  as  the  amount  of  antiserum 
to  be  injected.  The  injection  should  be  made 
slowly  and  carefully  to  avoid  the  production  of 
symptoms  due  to  increased  pressure.  This  pre- 
caution should  be  exercised  especially  where  the 
quantity  of  cerebrospinal  fluid  withdrawn  is  less 
than  the  amount  of  antiserum  to  be  injected. 

"The  injection  of  the  antiserum  should  be 
repeated  every  twenty-four  hours  for  three  or  four 
days  or  longer.  Whether  any  advantage  will  be 
gained  by  more  frequent  or  more  numerous  injec- 
tions than  here  indicated  a  wider  experience  must 
decide.  As  much  as  120  c.c.  of  the  antiserum  have 
been  injected  into  the  spinal  canal  in  four  days 
without  causing  unpleasant  symptoms. 

"The  evidence  indicates  that  the  earlier  in  tlie 
course  of  the  disease  the  injections  are  made  the 

5.  Flexner,  S.,  and  Jobling,  .T.  W. :  Jour.  Exp.  Med.,  1908, 
p.  190. 


INFLUENZA.  663 

better  the  results.  Hence,  should  the  film  jorep- 
aration  of  the  first  fluid  obtained  by  spinal  punc- 
ture show  Gram-negative  diplococci,  some  of  which 
are  within  leucocytes,  an  injection  should  be  made 
immediately  and  without  waiting  for  the  results 
of  culture  tests.  Should  the  diagnosis  be  left  in 
doubt  or  the  disease  prove  later  to  be  of  another 
nature  than  epidemic  meningitis,  no  harm  will  be 
done  by  the  injection  of  the  antiserum. 

"Although  the  best  results  have  thus  far  been 
obtained  where  the  antiserum  has  been  injected 
early  in  the  disease,  yet  the  serum  should  be  used 
in  its  later  stages  also  until  our  knowledge  gov- 
erning the  value  of  the  serum  becomes  more  pre- 
cise. The  indications  at  present  are  that  it  is 
useless  to  employ  the  serum  in  the  very  late  stages 
of  the  disease  in  which  chronic  hydrocephalus  is 
already  developed." 

Flexner  and  Jobling  conclude  from  an  analysis 
of  a  large  number  of  reports  of  the  use  of  anti- 
meningitis  serum,  that  the  serum  is  of  value  in 
reducing  the  period  of  illness  and  diminishing  the 
fatalities  due  to  the  disease.  The  figures  of  Dunn 
show  that  in  the  Boston  Children's  Hospital,  the 
i^iortality  before  the  use  of  the  serum,  from  69  to 
80  per  cent.,  was  reduced  to  below  20  per  cent, 
after  the  use  of  the  serum. 

VII.    INFLUENZA. 

Influenza  occurs  sporadically  and  in  epidemics 
of  greater  or  less  proportions.  Its  extreme  con- 
tagiousness is  shown  by  the  striking  rapidity  with 
which  it  spread  over  the  whole  civilized  world  in 
the  epidemic  of  1889  and  1890,  leaving  behind  it 
a  trail  of  lesser  epidemics  which  have  prevailed  up 
to  the  present  time. 


Value  of 
tlie  Serum, 


564  INFECTION     AND     IMMUNITY. 

Bacillus  During  the  epidemic  iust  cited  a  number  of  or- 
ganisms  were  erroneously  described  as  the  cause  of 
the  disease.  In  1892,  however,  Pfeiffer  discovered 
a  minute  bacillus  which  he  found  constantly  and 
in  large  numbers  in  the  sputum  of  influenza  pa- 
tients only.  The  observations  of  Pfeiffer  have 
been  confirmed  by  a  large  number  of  investigators, 
and  the  organism,  Bacillus  infiuenzoi,  is  now  ac- 
cepted as  the  cause  of  the  disease.  It  is  one  of  the 
smallest  of  bacteria  (0.2  or  0.3  by  0.5  microns),  is 
non-motile  and  forms  no  spores.  A  medium  con- 
taining blood  or  hemoglobin  is  essential  for  its 
artificial  cultivation,  and  even  under  the  best  con- 
ditions it  grows  meagerly  and  slowly.  A  number 
of  bloods,  but  particularly  those  of  man  and  the 
pigeon,  favor  its  groAvth.  It  is  a  strong  aerobe. 
The  organism  is  best  stained  by  a  dilute  solution  of 
carbol-fuchsin  (1  to  10),  and,  like  the  plague 
bacillus,  exhibits  polar  staining,  i.  e.,  the  ends 
stain  more  deeply  than  the  central  portion. 
Symbiosis.  \Vlien  the  staphylococcus  and  some  other  organ- 
isms are  grown  in  mixed  culture  with  the  influ- 
enza bacillus,  the  latter  is  stimulated  to  a  more 
vigorous  growth.  According  to  Jacobsohn,  killed 
cultures  of  the  streptococcus  greatly  increase  the 
virulence  of  the  influenza  bacillus  when  the  mix- 
ture is  injected  into  animals. 
Psencio-  Pfeiffer  designates  as  pseudoinfluenza  bacilli  a 
Baci^ih  number  of  influenza-like  organisms  which  have 
been  found  in  man  and  animals.  They  have  the 
morphology  of  the  influenza  bacillus,  are  a  little 
larger,  and  also  prefer  a  medium  which  contains 
hemoglobin,  but  since  some  of  them  occur  in  ani- 
mals which  are  known  not  to  be  susceptible  to  in- 
fluenza, it  is  concluded  that  they  can  not  be  identi- 


INFLUENZA.  565 

cal  with  the  influenza  bacillus.  The  influenza-like 
bacillus  which  Jochmann  and  Krause  consider  as 
the  cause  of  whooping-cough,  may  be  mentioned 
in  this  connection. 

The  resistance  of  the  bacillus  to  desiccation,  and***^"*^^ 
sunlight  and  unfavorable  temperatures  is  very  low.  virulence. 
It  dies,  in  from  twenty-four  to  thirty-six  hours  at 
room  temperature,  when  contained  in  sputum,  and 
lives  for  about  thirty-two  hours  in  hydrant  water 
(Pfeiffer).  It  is  not  highly  virulent  for  animals, 
although  a  condition  said  to  resemble  influ- 
enza has  been  produced  in  monkeys  by  placing 
pure  cultures  on  the  nasal  mucous  membrane. 
Fatal  infections  may  be  produced  by  intra- 
venous inoculation  of  the  bacillus  into  monkeys 
and  rabbits,  and  killed  cultures  produce  a  fatal 
intoxication  in  rabbits.  Virulent  cultures  in  suffi- 
cient quantity  produce  fatal  peritonitis  in  guinea- 
pigs.  Since  the  bacilli  seem  not  to  proliferate 
when  fatal  quantities  are  injected  intravenously 
into  rabbits,  and  since  fatal  intoxication,  without 
the  occurrence  of  bacteriemia,  may  take  place 
when  a  tracheal  infection  is  induced  in  the  ape 
(Pfeiffer),  it  is  concluded  that  the  toxic  phenom- 
ena of  influenza  are  due  to  the  absorption  of  bac- 
terial toxins  from  the  mucous  surfaces.  A  soluble 
toxin  has  not  been  obtained  in  culture  media.  The 
organism  is  a  facultative  pus  producer. 

So  far  as  is  known,  the  influenza  bacillus  is  ex-  pistribotion 

-'  m  tlie  Body. 

creted  only  with  the  secretions  of  infected  surfaces, 
i.  e.,  from  the  upper  respiratory  passages,  con- 
junctiva, ear,  etc.  The  belief,  commonly  held, 
that  the  influenza  bacillus  does  not  enter  the  cir- 
culation probably  is  erroneous.  That  metastatic 
infection  is  possible,  by  way  of  the  hmiph  or  blood 


566  INFECTION     AND     IMMUNITY. 

channels,  is  shown  by  the  occurrence-  of  influenza 
meningitis,  and,  rarely,  of  influenza  peritonitis 
(Hill  and  Fisch).  According  to  Jehle,  the  influ- 
enza bacillus  invades  the  blood  very  frequently  in 
some  of  the  acute  exanthemata.  It  was  found  in 
the  blood  in  22  out  of  48  cases  of  scarlet  fever,  in 
15  of  23  cases  of  measles,  and  in  5  of  9  cases  of 
varicella  (cited  by  Hektoen).  Hence,  these  dis- 
eases would  seem  to  create  conditions  favorable  for 
./ivasion  by  this  bacillus.  When  the  bacilli  reach 
the  blood  they  probably  are  killed  quickly.  It  is 
probable  that  the  ordinary  nervous  phenomena  of 
the  disease  are  due  to  intoxication  rather  than  to 
actual  infection  of  the  nervous  structures.  As  to 
whether  the  symptoms  of  so-called  intestinal  in- 
fluenza are  due  to  an  invasion  of  the  intestines 
by  the  bacilli  or  to  a  specialized  action  of  circu- 
lating toxin  seems  not  to  have  been  definitely  set- 
tled. There  certainly  is  abundant  opportunity  for 
infection  of  the  intestines  in  cases  of  bronchial 
influenza.  In  the  bronchitis  of  influenza  the  or- 
ganisms are  found  in  large  numbers  in  the  smaller 
bronchial  tubes,  both  free  and  within  leucocytes, 
hence,  in  searching  for  the  bacilli  clinically  it 
should  be  certain  that  the  sputum  examined  repre- 
sents the  bronchial  exudate.  In  influenza  pneu- 
monia, which  usually  is  of  the  lobular  type,  the 
bacilli,  mixed  with  pus  cells  and  contained  in 
them,  are  found  in  large  numbers  in  the  alveoli. 
Pure  cultures  of  the  bacillus  have  been  obtained 
from  cases  of  conjunctivitis,  and  they  occur  not 
infrequently  in  middle-ear  complications  which 
develop  during  the  course  of  the  disease.  Influ- 
enza conjunctivitis  sometimes  occurs  in  epidemic 
form,  particularly  in  institutions  and  schools. 


INFLUENZA. 


567 


Pneumonic  foci  which  develop  during  influenza  Mixed 
frequently  show  the  pneumococcus,  and  sometimes 
the  streptococcus  or  the  bacillus  of  Friedlander  in 
addition  to  the  influenza  bacillus^  and  similar 
mixed  infections  occur  in  pleurisy  and  in  middle- 
ear  diseases.  Influenza  may  be  superimposed  on 
other  infections;  individuals  suffering  from  pul- 
monary tuberculosis  are  particularly  susceptible  to 
influenza^  and  in  them  the  prognosis  is  unfavor- 
able. 

The  disease  is  transmitted  directly  from  man  to  Transmission, 

^  Infection 

man  and,  chiefly,  it  is  supposed,  by  means  of  in-   Atria  and  _ 

fected  droplets  of  sputum  which  are  expelled  in 
coughing  and  sneezing.  Obviously  kissing  affords 
opportunity  for  infection.  Infection  by  indirect 
contact  is  of  less  importance  because  of  the  rapid 
death 'of  the  bacillus  after  it  leaves  the  body,  but 
living  germs  may  well  be  disseminated  by  soiled 
handkerchiefs  or  other  contaminated  linen.  Dust 
infection  possibly  is  of  minor  consequence.  Chronic 
influenza  in  which  the  bacilli  may  persist  in  the 
bronchi  for  weeks^  and  cause  recurrent  acute  at- 
tacks, is  of  importance  for  the  maintenance  of  an 
epidemic.  In  tuberculous  cavities  the  bacilli  may 
flourish  for  long  periods. 

Primary  infection  takes  place  in  the  upper  res- 
pitory  passages,  and  the  disease  extends  readily 
from  one  surface  to  another,  as  from  the  nose  to 
the  pulmonary  tissue.  Infection  of  the  ear  usually 
is  a  complication  of  pharyngeal  or  pulmonary  in- 
fection. Occasionally  an  influenza  conjunctivitis 
is  found  without  other  localization.  "Primary" 
infection  of  other  organs,  as  the  brain  and  perito- 
neum, are  metastatic,  although  the  original  focus 
or  atrium  may  not  be  observed. 


568  INFECTION     AND     IMMUNITY. 

Little  or  nothing  can  be  done  in  the  wa}'  of 
general  proph3daxis.  Washing  of  the  nose  and 
mouth  with  antiseptics  during  an  epidemic  may 
reasonabl}^  be  practiced,  but  with  what  success  is 
uncertain.  The  aged  and  those  of  low  vitality 
should  avoid  exposure  to  infection,  for  in  them  the 
severer  complications,  such  as  pneumonia,  are 
more  likely  to  occur.  When  influenza  conjuncti- 
vitis appears  epidemically  in  schools,  the  latter 
should  be  closed  or  the  infected  children  excluded. 
immnnity,  Althougli  Httlc  or  nothing  is  known  concerning 
biiity^ami  ^^^^  possibility  of  a  natural  immunity  in  man,  ex- 
Recnrrences.  pericncc  tcachcs  that  he  is,  on  the  whole,  very  sus- 
ceptible. The  belief  expressed  by  some  that  nurs- 
ing children  are  less  susceptible  than  older  people 
seems  to  have  some  foundation,  although  it  is  well 
known  that  they  are  not  entirely  immune.  Influ- 
enza is  sometimes  cited  as  an  infection  in  which 
one  attack  creates  a  predisposition  for  a  second, 
but  the  truth  of  this  is  doubted  by  many  who  have 
had  extensive  experience  with  the  disease.  Wutz- 
dorff,  in  a  study  of  the  epidemic  which  prevailed 
in  Germany  during  1891-92,  finds  in  the  small 
number  of  cases,  the  irregularity  of  their  distribu- 
tion, and  compartive  exemption  of  rather  large 
districts,  reasons  for  believing  that  one  attack  con- 
fers a  degree  of  acquired  immunity;  that  is  to  say, 
the  population  had  been  so  thoroughly  infected 
during  the  preceding  year  or  two  that  compara- 
tively few  remained  who  were  susceptible,  although 
the  disease  itself  appeared  to  be  more  malignant 
than  in  the  previous  j'ear  (cited  from  Beck), 
However,  the  occurrence  of  second  attacks  shortly 
after  the  first,  and  of  repeated  infections  in  some 
individuals  indicate  that  acquired  immunity  is  of 


Properties. 


SOFT     CHANCRE.  569 

short  duration.  The  aged,  those  of  low  vitality, 
and  those  with  pulmonary  tuberculosis,  have  low 
resistance  to  infection. 

Although  Delius  and  Kolle  were  able  to  produce  serum 
a  slight  increase  in  the  resistance  of  guinea-pigs 
by  the  intraperitoneal  injection  of  cultures,  noth- 
ing* like  a  well-marked  immunity  was  obtained ; 
nor  did  the  serum  of  immune  animals  or  convales- 
cent man  show  increased  protective  power  for 
other  animals.  Slatineano,  however,  obtained 
serum  of  some  protective  value  for  guinea-pigs, 
by  the  immunization  of  rabbits  and  guinea-pigs, 
but  it  had  no  curative  effect.  The  results  of  Can- 
tani  were  similar,  and  both  observers  noted  the  de- 
velopment of  bactericidal  power,  as  determined  by 
the  Pfeiffer  reaction,  and  of  agglutinins.  At  pres- 
ent there  seems  little  to  hope  from  vaccination. 

There  is  said  to  be  some  increase  in  agglutinins 
in  man  as  a  consequence  of  infection.  The  agglu- 
tinating power  of  the  serum  of  an  immunized  ani- 
mal may  be  as  high  as  1  to  500  (Cantani). 

VIII.    SOFT    CHANCRE. 

The  independence  of  soft  chancre  and  syphiliy, 
and  the  infectiousness  of  the  former  by  inoculation 
with  the  purulent  secretions  of  the  ulcers,  were 
established  long  ago.  Eollet  found  that  filtered 
pus  lost  its  infectiousness. 

A  large  number  of  observers  had  found  bacteria  Baciiius  of 
of  one  kind  or  another  in  the  pus  and  in  stained 
sections  of  the  walls  of  the  ulcers,  and  probably 
some  of  them  (e.  g.,  Unna),  had  seen  the  bacillus 
which  Ducrey  described  (1889)  and  later  culti- 
vated, and  which  is  now  proved  to  be  the  cause  of 
the  disease.     The  bacillus  is  very  small   (0.4x1.5 


570  INFECTION     AND     IMMUNITY. 

microns),  is  non-motile  and  shows  polar  staining. 
It  resembles  the  plague  bacillus  in  form,  but  is 
somewhat  smaller,  and  does  not  show  the  exten- 
sive involution  forms  of  the  latter.  In  the  ulcer 
it  lies  singly,  in  small  groups,  or  more  characteris- 
tically in  the  form  of  bands,  made  up  of  two  or 
more  parallel  chains,  which  infiltrate  the  wall  of 
the  ulcer.  Large  numbers  are  often  found  in  the 
polymorphonuclear  leucocytes  of  the  pus,  par- 
ticularly at  an  early  stage  of  the  lesion  (Kraeft- 
ing).  Great  difficulty  was  encountered  in  culti- 
vating the  bacillus,  and  Ducrey's  first  success  was 
obtained  with  a  medium  which  contained  human 
skin.  It  has  since  been  cultivated  on  agar  which 
contains  the  blood  or  serum  of  man,  rabbit  or 
dog.  Himmel  attempted  to  cultivate  it  in  the 
fresh  defibrinated  blood  of  the  guinea-pig,  but 
was  unsuccessful  because  the  bacilli  were  phago- 
cytized  by  the  leucocytes  (Babes). 

An  ulcer  resembling  that  of  soft  chancre  may 
be  produced  in  the  ape,  and  also  in  the  cat,  by  the 
inoculation  of  pure  cultures.  Didey  reinoculated 
man,  successfully,  from  the  ulcers  of  the  cat. 
When  living  cultures  are  injected  into  the  guinea- 
pig  (peritoneal  cavity,  subcutaneous  tissue,  dura 
mater),  the  bacilli  are  quickly  taken  up  by  leuco- 
cytes and  digested  (Himmel).  Himmel  reports 
having  so  decreased  the  resistance  of  guinea-pigs 
by  peritoneal  injections  of  lactic  acid  that  they 
became  susceptible  to  infection.  After  two  or 
three  passages  the  culture  became  so  virulent  that 
fatal  bacteriemia  was  caused  without  previously 
lowering  the  resistance  of  the  animals. 


FRIEDLANDER'S     BACILLUS.  571 

In  man  the  infection  is  transmitted  to  the  in- 
guinal lymph  glands,  but  never  becomes  general. 

One  attack  in  man  does  not  confer  lasting  im- 
munity. Spontaneous  recovery  occurs,  but  its 
cause  is  not  known.  Inasmuch  as  the  bacilli  are 
found  within  leucocytes,  phagocytosis  may  be  a 
factor  in  recovery.  The  readiness  with  which  the 
autoinoculation  of  adjacent  skin  takes  place,  even 
after  the  disease  has  existed  for  some  time,  sug- 
gests that  general  immunity  is  not  established. 

IX.    BACILLUS    OF    FRIEDLAXDER    AND    OTHER    MEM- 
BERS   OF    THE    CAPSULE-FORMING    GROUP. 

The  bacillus  of  Friedlander,  or  Bacillus  pneu-  capsuiated 
monicBj  is  the  type  of  a  rather  large  group  of  bac- 
teria, called  the  Friedlander  group,  or  the  group 
of  Bacillus  mucosus  capsulatus.  In  addition  to 
the  ability  to  produce  a  mucus-like  capsule  or  en- 
velop, they  have  in  general  the  following  charac- 
teristics (Abel)  :  short,  plump  rods,  varying  in 
their  proportions,  having  no  motion,  no  flagella, 
no  spore  formation,  and  not  staining  by  Gramas 
method.  They  form  mucus-like  masses  in  cul- 
tures, do  not  liquefy  gelatin  and  are  facultative 
anaerobes.  They  are  widely  distributed  in  nature, 
vary  from  innocuousness  to  extreme  pathogenicity 
for  animals,  are  rarely  found  in  the  mouth,  nose 
and  bronchi  normally  (bacillus  of  Friedlander), 
one  type  being  a  normal  inhabitant  of  the  intes- 
tines, especially  in  children  (B.  laciis  aerogenes). 
Perkins  has  been  able  to  classify  the  members  of 
this  group  on  the  basis  of  their  fermenting  powers 
for  lactose  and  saccharose.  He  found  their  viru- 
lence for  animals,  immunization  and  agglutination 
tests,  too  variable  to  serve  as  bases  for  classifica- 


572 


INFECTION     AND     IMMUNITY. 


Pnenmonia 

Caused  by 

Friedlancler's 

Bacillus. 


Rliiiioscle- 

roma  and 

Ozena. 


tion.  In  man  three  members  of  the  group — they 
may  be  the  same  organism  or  variations  of  a  type 
— are  of  interest  from  the  standpoint  of  infection : 
Bacillus  of  Friedlander,  the  bacillus  of  rhinoscle- 
roma  and  the  ozena  bacillus. 

In  129  cases  of  acute  inflammation  of  the  lungs, 
Weichselbaum  found  the  bacillus  of  pneumonia 
nine  times,  twice  with  streptococci  and  once  with 
the  diplococcus  of  pneumonia.  The  organism 
causes  lobular  pneumonia  more  frequently  than 
lobar.  The  homogeneous  non-granular  surface, 
and  the  large  amount  of  fluid  of  a  viscid  or  mu- 
cous consistence,  are  characteristic  anatomic  feat- 
ures. The  alveoli  contain  massive  numbers  of  the 
bacilli.  The  bacillus  of  Friedlander  is  found  also 
as  the  cause  of  pyelitis,  cystitis,  pyelonephritis, 
serous  or  purulent  pericarditis,  pleuritis  and 
meningitis,  which  may  be  accompanied  by  brain 
abscesses.  Meningitis  when  produced  by  this  or- 
ganism usually  or  always  is  secondary  to  infection 
in  other  parts  of  the  body  by  the  same  organism 
(middle  ear  and  accessory  sinuses  of  the  nose). 

An  organism  of  the  Friedlander  type  is  found 
with  few  exceptions  in  the  tissues  in  rhinoscle- 
roma,  and  by  many  is  considered  as  the  cause  of 
the  condition.  A  similar  organism  is  found  con- 
stantly in  the  secretions  and  crusts  in  ozena. 

Antiserums  of  distinct  power  have  not  been  ob- 
tained for  members  of  the  group.  Prolonged  im- 
munization with  some  strains  yields  an  agglutinat- 
ing serum  of  low  value.  The  agglutination  re- 
action is  of  no  value  for  identification  of  the  dif- 
ferent members  of  the  group,  nor  for  clinical" 
diagnosis. 


CHAPTER  XXVII. 
GROUP  IV. 


Infectious  diseases  which  usually  are  chronic, 
but  may  run  acute  courses.  They  are  characterized 
by  marked  local  tissue  changes,  which  exert  a  lim- 
iting influence  on  the  processes,  and  include  the 
infectious  granulomata,  excepting  syphilis.  Infec- 
tion produces  little  or  no  immunity.  In  some  in- 
stances the  prolonged  immunization  of  animals  in- 
duces increased  resistance  to  infection  (tuberculo- 
sis) ;  in  other  instances  this  has  not  been  deter- 
mined, or  is  difficult  of  determination  because  of 
the  non-susceptibility  of  the  animals  used  to 
the  corresponding  infections.  The  serums  of  im- 
munized animals,  in  so  far  as  this  subject  has  been 
investigated,  show  little  or  no  protective  or  cura- 
tive power. 

I.    TUBERCULOSIS. 

Klemke,  in  1843,  but  more  particularly  Ville- 
min,  in  1865,  demonstrated  the  infectiousness  of 
tuberculosis  by  animal  experiments,  and  these  re- 
sults were  substantiated  later  by  such  investigators 
as  Klebs,  Chauveau,  Baumgarten  and  Cohnheim. 
Baumgarten  first  saw  the  tubercle  bacillus  in  sec- 
tions of  tuberculous  material  from  which  the  tis- 
sue cells  had  been  dissolved  by  potassium  hydroxid, 
and  at  almost  the  same  time  Koch  succeeded  in 
demonstrating  its  presence  in  all  tuberculous 
lesions  by  a  special  staining  method.  He  eventu- 
ally obtained  the  organism  in  pure  cultures  with 


574  INFECTION     AND     IMMUNITY. 

which  he  again  produced  tuberculosis  in  experi- 
ment animals. 
characteris-  The  tubeicle  bacillus  is  an  obligate  aerobic  para- 
*Siciiins,  site,  has  the  form  of  a  slender,  non-flagellated  rod, 
often  slightly  curved,  from  2  to  4  microns  long 
and  from  0.3  to  0.5  microns  broad.  In  stained  and 
even  in  unstained  specimens,  when  properly 
treated,  a  number  of  spherical,  oval  or  elongated 
clear  spaces  can  be  seen  which  Koch  at  one  time 
thought  to  be  spores.  They  are  now  considered 
either  as  vacuoles,  or  as  representing  some  form  of 
degeneration  or  reserve  nutritious  material.  Spore 
formation  is  uncertain.  The  organism  is  sup- 
posed to  possess  a  membrane  which  may  be  re- 
sponsible for  its  strong  resistance  against  heat  and 
desiccation.  Feinberg  speaks  of  a  nucleus  (?)  which 
may  be  demonstrated  by  a  modified  Eomanowsky 
stain.  The  organism  shows  many  variations  in  its 
morphology  under  different  conditions.  It  often 
exists  in  isolated  clumps,  either  in  cultures  or  in 
tissues,  and  may  be  excreted  as  such  in  the  urine. 
In  certain  cultures  and  sometimes  in  animal  tis- 
sues it  grows  in  the  form  of  longer  or  shorter 
branching  threads,  in  this  respect  resembling  acti- 
nomyces.  This  last  occurrence  has  led  a  number 
of  authorities  to  class  the  tubercle  bacillus  as  a 
streptothrix,  while  others  would  give  it  an  inter- 
mediate position  between  true  bacteria  (schizoray- 
cetes)  and  the  streptothrix  (a  hyphomyces).  Oval 
or  spherical  degeneration  forms,  the  capsules  or 
corpuscles  of  Schron,  are  found  in  advanced  tuber- 
culosis of  the  lymph  glands  and  other  organs  in 
which  there  is  a  great  deal  of  necrosis. 

The  tubercle  bacillus  is  one  of  a  group  of  organ- 
isms which   are  said  to  be   "acid   fast"  in   their 


TUBERCLE     BACILLUS. 


575 


staining 
Properties. 


staining  properties.  When  stained  with  the  carbol 
fuchsin  of  Ziehl  and  subjected  to  the  action  of 
mineral  acids  in  dilute  solutions  the  fuchsin  is  not 
removed.  After  counterstaining  with  methylene 
blue,  the  tubercle  bacilli  appear  red,  whereas  other 
organisms,  not  "acid  fast,"  are  stained  with  the 
methylene  blue.  It  is  not  difficult  to  recognize  the 
bacilli  in  sections  of  tissue  when  the  proper  technic 
is  used,  although  the  search  is  at  times  a  laborious 
one.  In  old  processes  the  organism  often  can  not 
be  recognized,  and  recourse  to  animal  inoculation 
may  be  necessary  in  order  to  demonstrate  the  ex- 
istence of  tuberculosis. 

Much  has  demonstrated  in  such  cases,  however, 
the  presence  of  granular  forms  of  tubercle  bacilli 
which  are  not  acid  fast  but  which  stain  by  a  modi- 
fication of  Gram's  method. 

Ordinarily  it  is  a  difficult  task  to  obtain  the  Cultivation 
tubercle  bacillus  in  pure  culture,  and  the  technic 
we  need  not  consider  here.  Even  under  the  best 
conditions  growth  is  very  slow,  and  may  not  be 
recognizable  to  the  naked  eye  for  from  six  to  ten 
days.  Coagulated  bovine  serum  to  which  has 
been  added  from  2  to  4  per  cent,  glycerin  is  the 
most  favorable  culture  medium.  Good  growth  oc- 
curs also  in  glycerin  agar,  in  glycerin  bouillon 
and  on  potatoes.  The  optimum  temperature  is  37° 
C. ;  growth  does  not  occur  above  42°  C.  nor  below 
30°  C.  When  a  small  amount  of  culture  is  planted 
on  the  surface  of  glycerin  bouillon  it  proliferates 
slowly*  to  form  a  heavy  membrane.  In  time  this 
growth  sinks  from  its  own  weight  and  a  new  mem- 
brane forms.  This  process  continues  until  large 
masses  have  accumulated  at  the  bottom  of  the 
flask. 


576  INFECTION     AND     IMMUNITY. 

Resistance.  In  its  resistance  to  desiccation  the  tubercle  ba^ 
cillus  is  exceeded  only  by  spore-forming  organisms ; 
it  lives  approximately  for  three  months  in  dried 
sputum  which  appears  to  form  a  protective  coat- 
ing about  it.  Direct  sunlight  destroys  it  in  a  few 
hours  at  the  most,  whereas  diffuse  light  kills  it 
only  after  from  five  to  seven  days  (Koch).  It  is 
said  that  the  guinea-pig  when  exposed  to  sunlight 
withstands  tuberculosis  for  a  longer  time  than  one 
which  is  kept  in  the  dark.  Roentgen  rays  are  bac- 
tericidal for  the  organism,  killing  it  in  about  one 
hour  (Rieder).  Under  moist  heat  a  temperature 
of  55^  C.  kills  it  in  from  four  to  six  hours,  60°  C. 
in  one  hour,  70°  C.  in  from  ten  to  twenty  minutes, 
80°  C.  in  five  minutes,  from  90°  to  95°  C.  in  from 
one  to  two  minutes.  When  embedded  in  sputum 
it  is  more  resistant,  five  minutes  being  required  to 
kill  it  at  the  boiling  temperature.  Corrosive  sub- 
limate is  not  a  good  disinfectant  in  this  case,  inas- 
much as  it  produces  an  albuminous  precipitate 
around  the  organism  which  prevents  penetration 
of  the  sublimate.  Five  per  cent,  carbolic  acid 
added  to  equal  parts  of  sputum  kills  the  bacil- 
lus in  24  hours.  Formalin  vapor  is  a  good  dis- 
infectant for  dr}^,  but  not  for  moist  sputum.  Iodo- 
form is  not  a  good  disinfectant,  in  spite  of  its  bene- 
ficial influence  on  the  infectious  process.  The  re- 
sistance of  the  bacillus  to  gastric  digestion  has  an 
important  bearing  on  the  occurrence  of  infection 
in  the  intestinal  tract.  The  gastric  juice  of  the 
dog,  in  one  instance,  failed  to  kill  the  bacillus  after 
six  hours'  exposure,  although  it  had  the  power  of 
prohibiting  proliferation. 
viraience.  The  bacillus  of  humau  tuberculosis,  although 
fairly  constant  in  its  virulence,  may  be  attenuated 


TUBERCLE     BACILLUS.  511 

by  various  means.  Its  prolonged  existence  in  putrid 
sputum  decreases  its  virulence  and  a  similar  de- 
crease occurs  on  potato,  in  old  cultures  or  in  those 
which  contain  iodoform,  boracic  acid  and  some 
other  substances.  Inoculation  with  such  cultures 
produces  a  chronic  form  of  tuberculosis  in  animals 
which  may  heal.  In  other  instances  cultures  which 
have  grown  on  artificial  media  for  many  years  re- 
tained their  original  virulence. 

The  organism  contains  about  90  per  cent,  of 
water.  One-fourth  of  a  dried  bacterial  mass  may 
be  extracted  as  a  wax-like  or  fat-like  substance  by 
a  mixture  of  alcohol  and  ether.  The  acid-fast 
staining  property  of  the  bacillus  depends  on  this 
substance.  The  remaining  portion  of  the  mass, 
consisting  largely  of  proteins,  which  may  be  ex- 
tracted by  dilute  alkalies,  contains  a  toxic  nucleo- 
albumin.  Cellulose,  representing  a  portion  of  the 
capsular  substance,  is  also  found  in  the  residue. 

Killed  cultures  when  given  subcutaneously  pro-  toxIc 
duce  necrosis,  abscesses,  caseation,  marasmus,  and 
a  subnormal  temperature.  When  given  to  rabbits 
and  guinea-pigs  intravenously  they  cause  rapid 
emaciation  and  death  in  from  a  few  days  to  a  few 
weeks.  By  beginning  with  very  minute  doses,  how- 
ever, the  animals  may  be  gradually  habituated  to 
intoxication  by  the  dead  bacilli  and  eventually 
withstand  large  doses.  The  same  holds  true  of  the 
various  toxic  substances,  including  tuberculin, 
which  may  be  extracted  from  cultures.  The  pro- 
teins and  alkaline  extracts  cause  abscesses  when 
given  subcutaneously.  The  fever-producing  sub- 
stance which  is  present  in  the  preparations  men- 
tioned below  is  one  of  the  metabolic  products  of 
the  bacillus,  rather  than  a  constituent  of  the  bac- 


Producta. 


578  INFECTION     AND     IMMUNITY. 

lerial  cell  (Koch).  This  substance  is  100  times 
as  toxic  for  tuberculous  animals  as  for  healthy  and 
causes  an  increase  in  the  eosinophiles  of  the  blood. 
In  addition  to  the  fever-producing  substance, 
Maragliano  and  others  recognize  as  a  constituent 
of  the  bacillus  a  heat  susceptible  "toxalbumin" 
(destroyed  at  100°  C.)  which  reduces  temperature. 
Hammerschlag  speaks  of  a  toxin  which  in  animals 
causes  fatal  convulsions.  The  toxic  products  of  the 
tubercle  bacillus  show  their  greatest  toxicity  when 
injected  into  the  brain,  and  this  method  of  injec- 
tion has  been  suggested  "for  the  standardization  of 
tuberculin. 
Tuijercuiin.  Of  the  toxic  preparations  of  the  bacillus  the 
greatest  interest  attaches  to  tuberculin  which 
Koch,  in  1891,  announced  as  an  agent  which  could 
be  used  for  the  specific  diagnosis  of  tuberculosis 
and  which,  when  properly  administered,  had  cer- 
tain curative  effects.  Its  preparation  is  simple. 
Cultures  are  alloAved  to  grow  for  four  weeks  in 
peptone  bouillon  which  contains  5  per  cent,  of 
glycerin.  At  the  end  of  this  time  the  organisms 
are  killed  by  exposure  to  a  temperature  of  100°  C. 
for  one  hour  (Marx).  The  fluid  is  reduced  to  one- 
tenth  its  original  volume  by  evaporation  under  a 
vacuum  at  a  low  temperature  and  the  bacterial 
cells  are  eventually  removed  by  filtration.  The 
percentage  of  glycerin  which  is  present  in  the  final 
preparation  acts  as  a  preservative,  but  0.5  per 
cent,  carbolic  acid  may  be  added  in  addition.  The 
active  substance  in  tuberculin  may  be  precipitated 
by  66  per  cent,  alcohol;  its  chemical  nature  re- 
mains imknown. 

In  addition  to  the  "old  tuberculin,"  which  has 
just  been  described,  Koch  has  made  several  other 


TUBERCULIN.  579 

preparations  having  similar  properties,  the  use  of  "ta,"  "tr" 
which  has  been  proposed  for  diagnostic  and  cura-  *"  ^*'* 
tive  purposes  and  for  convenience  in  carrying  out 
the  agglutination  reaction.  One  of  these,  "TA/^ 
is  an  alkaline  preparation  which  is  made  by  ex- 
tracting cultures  with  1/10  normal  sodium  hy- 
droxid  solution.  Its  diagnostic  value  was  equal 
to  or  exceeded  that  of  tuberculin  because  of 
the  longer  duration  of  the  reaction.  However,  in 
view  of  the  fact  that  it  contained  undissolved 
cells,  which  caused  the  formation  of  abscesses  at 
the  point  of  injection,  its  use  was  not  encouraged. 
For  purposes  of  immunization  Koch  prepared  a 
fluid  which  contained  all  the  bacterial  constituents 
and  which  at  the  same  time  is  readily  absorbed 
without  abscess  formation.  For  its  preparation 
dried  masses  of  the  organism  are  ground  up  in  an 
agate  mortar;  after  suspension  in  distilled  water 
and  centrifugation,  the  emulsion  consists  of  two 
layers.  The  overlying  opalescent  whitish  fl.uid  was 
designated  as  "TO"  {Tuberculin-Ohers) .  After 
removal  of  the  fluid  from  the  precipitate  the  lat- 
ter was  again  dried  and  ground,  suspended  in 
water  and  centrifugated  as  before,  and  the  process 
repeated  until  none  of  the  sediment  remained.  The 
different  fractions  of  fluid,  except  the  "TO,"  were 
combined  to  constitute  "TR"  (Tuherculin-Rest) , 
which  is  really  an  emulsion  of  minute  fragments 
of  cells.  It  is  readily  absorbed  and  does  not  cause 
the  formation  of  abscesses.  This  is  commonly 
called  Koch's  "new  tuberculin."  Still  another 
preparation  which  Koch  later  devised  for  active 
immunization  and  for  convenience  in  performing 
the  agglutination  test  consists  of  dried  and  ground 
up  bacilli  which  are  suspended  in  equal  parts  of 


ization. 


580  INFECTION     AND     IMMUNITY. 

glycerin  and  water,  Neutuherculin  Koch  (Bazillen- 
emulsion) . 
other  Preparations  which  in  many  respects  are  analo- 
ercn  ms.  g^^g  ^^  those  of  Koch  have  been  made  by  various 
investigators;  the  tuberculocidin  of  Klebs,  the  tu- 
berculins of  de  Schweinitz  and  Dorset  and  that  of 
Denys,  the  two  tubercule  toxins  of  Maragliano, 
which  he  utilizes  for  the  preparation  of  antitoxic 
serums,  the  oxytuberculin  of  Herschfelder,  the 
"TD"  and  the  "TDE"  of  Behring  and  the  tubercu- 
loplasmin  of  Buchner.  Marmorek  claims  to  have 
obtained  the  true  toxin  of  the  tubercle  bacillus  by 
growing  young,  vigorous  cultures  on  a  complicated 
medium,  denying  that  tuberculin  represents  the 
true  toxin  of  the  organism. 
standard-  TubercuHu  Can  not  be  standardized  with  accur- 
acy. Because  of  the  extraordinary  susceptibility  of 
tuberculous  animals  to  tuberculin,  Koch  decided  to 
estimate  its  value  by  the  quantity  required  to  kill 
such  animals.  From  0.5  to  1  c.c.  of  tuberculin, 
when  injected  into  a  healthy  guinea-pig,  causes 
neither  a  local  nor  a  general  reaction,  whereas 
from  0.1  to  0.15  c.c.  kills  a  tuberculous  guinea- 
pig  in  from  24  to  48  hours.  For  stand- 
ardization von  Lingelsheim  recommends  intracere- 
bral injection  into  healthy  guinea-pigs,  because 
of  the  extreme  toxicity  of  tuberculin  when 
introduced  into  the  central  nervous  system;  only 
1/180  as  much  tuberculin  was  required  to  cause 
death  by  intracerebral  injections  as  compared  with 
subcutaneous  or  intraperitoneal.  Behring  bases  the 
value  of  tuberculin  on  its  toxicity  for  healthy 
guinea-pigs  and  in  his  terms  the  expression  "1 
c.cm.  =  1,000  M."  means  that  one  gram  of  the 
toxin  is  fatal  to  1,000  grams  of  guinea-pig  tissue. 


TUBERCULIN.  581 

His  "TD^'  has  a  value  of  1,250  M.,  and  "TDK," 

12,500  M.  For  the  standardization  of  old  tuber- 
culin, the  following  method  is  used  in  the  Eoyal 
Institute  for  Experimental  Therapy,  at  Frankfort, 
Germany:  Two  series  of  guinea-pigs  infected 
with  a  pure  culture  of  tubercle  bacilli  are  injected 
with  decreasing  doses  of  tuberculin.  In  one  series 
a  standard  preparation  of  tuberculin  is  used;  in 
the  second  series,  the  tuberculin  to  be  tested  is 
utilized.  If  the  minimum  fatal  dose  of  the  sample 
to  be  tested  is  the  same  as  the  standard,  it  is  of 
official  strensrth.  If  stron2:er  than  the  standard  it 
is  diluted  to  the  desired  strength.  If  weaker  it  is 
concentrated  by  further  evaporation. 

The  tubercle  bacillus  undergoes  no  proliferation 
outside  the  body  and  its  occurrence  in  nature  de- 
pends on  the  distribution  of  the  infected  excre- 
tions, particularly  the  sputum,  of  man.  Hence  it 
is  found  most  abundantly  in  the  rooms  and  homes 
of  patients  and  in  tuberculous  wards  of  hospitals. 
Reception  of  sputum  on  the  handkerchief  of  the 
patient,  where  it  subsequently  dries,  and  its  dis- 
charge on  the  iloor  in  public  places,  where  it  quick- 
ly becomes  pulverized,  as  in  street  cars,  are  condi- 
tions which  favor  dissemination  and  the  infection 
of  others.  In  unconfined  places  which  are  exposed 
to  the  action  of  light  and  sun,  as  the  streets  and 
sidewalks,  the  danger  is  less  on  account  of  the 
shorter  life  of  the  organism  under  these  conditions 
and  the  greater  volume  of  surrounding  air.  The 
calculation  of  Heller  that  a  tuberculous  patient 
may  excrete  7,200,000,000  of  bacilli  in  a  day  sug- 
gests the  number  which  may  lurk  in  a  single  mis- 
placed portion  of  sputum.    Sputum  which  is  kept 


Disseuii- 
natiou. 


Dried 
Sputum. 


582  INFECTION     AND     IMMUNITY. 

moist  is  not  a  source  of  particular  danger,  inas- 
much as  ordinary  currents  of  air  do  not  dissipate 
it  in  the  form  of  infected  drops.  Droplets  of  spu- 
tum which  are  expelled  by  coughing  contribute 
greatly  to  the  infected  dust  which  surrounds  a 
patient. 

Large  quantities  of  bacilli  are  often  "Ixcreted  in 
the  feces  in  intestinal  tuberculosis  and  in  the  urine 
in  genitourinary  tuberculosis,  or  in  general  miliary 
tuberculosis  with  localization  of  the  process  in  the 
urinary  organs.  The  pus  from  tuberculous  ab- 
scesses commonly  is  infectious. 
Boviuc  and  Great  interest  attaches  to  the  possibility  of  infec- 
berimiosis"  tiou  of  man  by  the  milk  and  meat  of  tuberculous 
cattle.  Previous  to  1901,  through  the  work  of 
Smith  and  others,  the  opinion  had  been  gaining 
ground  that  the  bacilli  of  human  and  bovine  tuber- 
culosis are  not  identical.  It  was  not  always  possi- 
ble to  produce  tuberculosis  in  cattle  by  feeding 
them  or  causing  them  to  inhale  tuberculous  spu- 
tum or  pure  cultures  which  were  highly  infectious 
for  other  experiment  animals,  although  bacilli  of 
bovine  origin  invariably  caused  the  disease  in  cattle 
when  administered  in  a  similar  manner.  It  seemed 
then  that  the  two  bacilli  are  not  identical  in  their 
pathogenic  powers.  Koch  having  performed  such 
experiments  without  being  able  to  infect  cattle  with 
bacilli  of  human  origin  expressed  his  belief  that 
the  converse  also  is  true,  i.  e.,that  the  bovine  ba- 
cillus is  not  pathogenic  for  man.  Perhaps  the 
strongest  argument  in  favor  of  this  view  is  the 
circumstance  that  primary  tuberculosis  of  the  in- 
testines and  mesenteric  glands  is  very  rare  in  chil- 
dren, who  drink  a  good  deal  of  milk,  in  spite  of 
the  great  prevalence  of  tuberculous  cows.     Manv 


TYPES     OF     TUBERCLE.  583 

protests  followed  the  announcement  of  Koch's 
views,  and  in  a  short  time  a  number  of  investiga- 
tors showed,  first,  that  it  is  possible  in  some  cases 
to  produce  tuberculosis  in  cattle  with  tuberculous 
material  from  man,  and,  second,  that  infection  of 
man  with  the  bovine  bacillus  is  possible.  Un- 
questionable proof  of  the  latter  consists  in  the  de- 
velopment of  localized  tuberculosis  in  those  who 
have  performed  autopsies  on  tuberculous  cattle 
(Eavenel  and  others).  In  an  examination  of  436 
cases  of  human  tuberculosis,  Park  and  Krumwiede 
found  bacilli  of  the  bovine  t3^pe  in  fifty-two  cases 
(11.9  per  cent.).  In  persons  over  16  years  of  age, 
constituting  297  of  the  436  cases,  one  case  of 
tuberculosis  with  bacilli  of  the  bovine  type  was 
found  (0.39  per  cent.).  In  children  between  the 
ages  of  5  and  16,  nine  out  of  fifty-four  cases  were 
due  to  the  bovine  type  of  bacilli  (18.5  per  cent.). 
In  eight3''-nine  cases  in  which  the  patients  were 
under  5  years  of  age,  twenty-two  due  to  the  bovine 
type  were  found  (nearly  one-fourth).  The  cases 
showing  bovine  types  of  bacilli  were  mostly  infec- 
tions of  the  abdomen  and  glands  of  the  neck.  In 
no  case  of  primary  pulmonary  infection  were 
bacilli  of  the  bovine  type  found. 

The  following  points  serve  to  distinguish  the  J^^J^^®***^®* 
bovine  bacillus  from  the  human :  First,  the  bovine  Bacim. 
bacillus  is  shorter  than  the  human;  second,  when 
first  cultivated  it  grows  feebly  in  media  in  which 
the  human  bacillus  flourishes;  third,  it  has  a 
higher  virulence  for  rabbits  and  guinea-pigs,  and, 
fourth,  it  produces  more  extensive  lesions  in  cattle. 
To  these  Smith  has  added  a  fifth  point,  which  he 
has  found  to  be  distinctive  in  a  large  number  of 


584  INFECTION     AND     IMMUNITY. 

C'liltures :  In  bouillon  which  contains  5  per  cent, 
of  glycerin  and  which  is  2  per  cent,  acid  to  phenol- 
phthalein  the  bovine  bacillus  produces  a  neutral 
or  faintly  alkaline  reaction  in  from  three  to  sev- 
eral weeks,  whereas  the  human  bacillus,  after  caus- 
ing temporary  alkalinity,  produces  a  terminal 
acidity  of  from  0.5  to  1.5  per  cent.  On  the  basis 
of  this  test  and  other  points  the  bacilli  of  two  cases 
of  mesenteric  tuberculosis  in  man  were  recognized 
as  bovine  in  type.  In  view  of  the  fact  that  infec- 
tion of  man  with  the  bovine  bacillus  has  been 
shown  to  be  possible,  we  are  justified  in  con- 
sidering the  meat  and  especially  the  milk  of  tuber- 
culous cattle  as  the  probable  sources  of  infection 
in  a  limited  number  of  cases. 
congrenitai       Comparatively  few  cases  of  undoubted  cono^cni- 

-nbercnlosls.  -^  .-^  .°, 

tal  tuberculosis  have  been  observed,  and  m  sucn 
cases  the  mothers  are  usually  in  an  advanced  stage 
of  the  disease.  It  is  probable  that  the  organisms 
reach  the  fetus  following  metastatic  invasion  of  the 
placenta.  In  a  number  of  cases  in  which  the 
mother  had  advanced  tuberculosis  the  organs  and 
blood  of  the  fetus  (stillborn  or  dying  soon  after 
birth),  contained  very  many  bacilli,  although  his- 
tologic lesions  had  not  as  yet  been  produced 
Warthin  and  Cowie  suggest  that  the  tissues  of  th^ 
fetus  may  possess  considerable  immunity  in  such 
cases.  Baumgarten  is  a  strong  believer  in  the  pos- 
sibility that  tubercle  bacilli  may  pass  to  the  fetus 
during  pregnancy  and,  remaining  latent  in  some , 
of  the  tissues  (lymph  glands)  for  a  long  period, 
cause  active  tuberculosis  later  in  life.  Others  who 
are  less  radical  still  admit  that  we  should  consider 
this  as  a  possibility   (Warthin  and  Cowie,  Har- 


INFECTION     ATRIA.  585 

bitz).  The  possibility  of  transmission  of  tubercu- 
losis by  means  of  tubercle  bacilli  in  the  spermatic 
fluid  should  also  be  considered.  Although  no 
proof  of  such  infection  exists,  the  presence  of 
bacilli  in  the  spermatic  fluid  has  been  demonstra- 
ted, particularly  in  men  with  tuberculous  epididy- 
mitis. 

Pulmonary  tuberculosis  is  by  far  the  most  com-  infection 
mon  form  of  the  disease  in  man,  and  without  doubt 
this  usually  is  due  to  inhalation  of  the  dried  and 
pulverized  sputum  of  tuberculous  patients.  Drop 
infection  may  well  occur  in  the  case  of  those  who 
are  in  intimate  contact  with  the  sick.  In  kissing, 
direct  infection  from  mouth  to  mouth  is  a  danger- 
ous possibility. 

The  reason  for  the  inception  of  pulmonary  tu- 
berculosis in  the  apex  in  so  many  cases  is  not  clear- 
ly recognized,  although  it  is  often  referred  to  the 
relative  immobility  of  this  tissue,  which  renders 
excretion  more  difficult  and  affords  improper 
aeration.  These  conditions  not  only  allow  the  or- 
ganisms to  accumulate  and  to  proliferate,  but  the 
insufficient  oxygenation  probably  causes  a  low  tis- 
sue resistance.  The  suggestion  which  has  been 
made  that  apical  tuberculosis  is  the  result  of  ex- 
tension of  the  disease  from  the  cervical  glands  does 
not  correspond  with  the  condition  seen  in  tubercu- 
losis of  adults  in  whom  the  cervical  adenitis  is 
commonly  wanting. 

The  "anatomic  tubercle"  is  a  primary  infection 
of  the  skin ;  lupus  vulgaris,  it  is  supposed,  may  be 
either  a  primary  infection  or  secondary  to  tubercu- 
losis in  some  other  organ;  ulcerative  tuberculosis 
is  usually  a  secondary  lesion,  often  occurring  by 
direct  extension  from  tuberculous  lymph  glands. 


586  INFECTION     AND     IMMUNITY. 

Tuberculosis  of  the  nose  is  uncommon.  Infection 
of  the  tonsils  is  not  infrequent  and  probably  is  a 
common  cause  of  secondary  tuberculosis  of  the  cer- 
vical lymph  glands.  Primary  infection  of  the 
pharynx  sometimes  occurs  and  large,  coarsa  granu- 
lations of  this  surface  have  been  proved  in  some 
cases  to  be  of  a  tuberculous  nature.  Tuberculosis 
of  the  pharynx  and  larynx,  however,  most  often 
arises  from  infection  with  tuberculous  sputum. 

In  the  process  of  dust  infection  of  the  lungs,  and 
also  by  other  means,  many  organisms  lodge  on  the 
mucous  membranes  of  the  nose,  mouth,  pharynx, 
trachea  and  larger  bronchi,  but  usually  without 
producing  a  tuberculous  infection.  On  account  of 
the  movement  of  the  ciliated  epithelium,  tortuos- 
ity of  the  nasal  channels,  excretion  of  the  bacilli 
with  mucus,  the  conditions  at  these  points  are  not 
favorable  for  infection. 

Tuberculous  ulcers  of  the  esophagus  and  stom- 
ach are  very  rare,  as  is  primary  tuberculosis  of  the 
intctotines.  Secondary  tuberculosis  of  the  intes- 
tines usually  is  caused  by  the  infected  sputum 
which  the  patient  swallows.  Primary  infection  of 
the  genital  organs  may  arise  from  direct  contact. 

That  tubercle  bacilli  have  often  been  found  on 
the  hands  and  finger  nails  of  the  sick  as  well  as  on 
those  who  are  intimately  associated  with  them  is  a 
significant  fact  in  relation  to  the  possibility  of  in- 
fection by  direct  contact. 
Metastases.  From  a  givcu  focus  tubercle  bacilli  extend  to 
other  structures  in  several  ways.  On  more  or  loss 
theoretical  grounds  one  speaks  of  "extension  by 
growth"  of  the  organism  into  contiguous  tissues. 
The  commonest  method  of  extension,  however,  is 


METASTASIS    IN     TUBERCULOSIS.  587 

that  of  metastasis  by  way  of  the  lymph  channels, 
When  bacilli  penetrate  a  surface,  with  or  withoui 
the  formation  of  a  lesion  at  the  point  of  entrance, 
as  in  the  mouth  cavity,  intestinal  canal,  or  bron- 
chial surface,  they  are  carried  to  the  lymph  glands 
of  the  region  in  which  the  tuberculous  process  is 
instituted.  As  in  plague,  the  infection  atrium  at 
times  is  indicated  by  the  set  of  glands  which  is  in- 
volved. In  certain  localities  the  secondary  invasion 
of  other  structures  takes  place  directly  without  the 
intermediate  involvement  of  lymph  glands,  as  in 
tuberculous  meningitis  caused  by  extension  from 
the  middle  ear,  and  tuberculous  peritonitis  or  peri- 
carditis by  extension  from  the  pleura.  Very  fre- 
quently tuberculosis  of  the  lymph  glands  and  other 
tissues  heals  spontaneously,  as  described  below. 
In  case  healing  does  not  occur,  metastases  con- 
tinue from  one  lymph  gland  to  another  and  to  new 
sets  of  glands  until  the  larger  lymph  channels  are 
reached,  as  a  consequence  of  which  extensive  re- 
localization  of  a  focus  often  causes  a  wide  depart- 
gional  or  general  tuberculosis  results.  Accidental 
localization  of  a  focus  often  causes  a  wide  depart- 
ure from  the  slow  development  just  described.  Not 
infrequently  tuberculosis  in  a  lymph  gland,  which 
is  contiguous  to  a  large  lymph  channel,  as  the  tho- 
racic duct,  invades  the  wall  of  the  latter,  the  sur- 
face softens  from  caseation  or  liquefaction  and  the 
contents,  imnresmated  with  countless  bacilli,  are 
gradually  thrown  into  the  circulation.  Miliary 
tuberculosis,  first  of  the  lungs  and  then  of  other 
tissues,  through  the  arterial  circulation,  follows 
such  an  accident.  A  similar  course  with  variations 
in  localization,  follows  invasion  of  the  walls  of 
branches  of  the  pulmonary  artery  or  vein.  Eup- 
ture  of  a  focus  into  a  bronchus  is  followed  by  re- 


588 


INFECTION     AND     IMMUNITY. 


The  Tubercle 

and  Otiier 

Tissne 

Cliang'es. 


gional  or  more  extensive  dissemination  of  the  ba- 
cilli throughout  the  lungs  by  respiratory  forces. 
A  slower  eccentric  extension  is  seen,  particularly 
in  the  lungs,  in  which  smaller  and  larger  areas  of 
consolidation  occur.  By  means  of  short  lymphatic 
metastases  into  contiguous  territory  new  foci  are 
instituted,  which  eventually  fuse  with  the  original 
lesion.  It  is  suggested  and  generally  believed  that 
bacilli  may  be  carried  longer  or  shorter  distances 
by  wandering  phagocytic  cells.  When  tuberculosis 
once  involves  a  surface  like  that  of  the  pleura,  peri- 
toneum, pericardium  or  pelvis  of  the  kidney,  the 
whole  surface  frequently  becomes  involved  in 
thickly  studded  miliary  tubercles.  It  is  probable 
that  a  great  deal  of  dissemination  is  accomplished 
by  the  movements  of  the  fluids  and  the  surfaces  of 
these  cavities.  In  other  instances,  as  in  the  ure- 
ters. Fallopian  tubes  and  spermatic  cords,  exten- 
sion seems  to  occur  in  the  submucous  tissue  by 
means  of  the  lymphatics.  The  autopsy  often  dis- 
closes that  tuberculosis  which  appeared  to  be  "pri- 
mary^' in  such  organs  as  bones,  suprarenal  glands, 
and  meninges  was  preceded  by  an  old  process  in  a 
lymph  gland  from  which  metastases  occurred  to  tlie 
tissues  in  question. 

Certain  anatomic  conditions  produced  in  tuber- 
culosis which  are  associated  with  recovery  from  the 
disease,  or  the  contrary,  may  be  referred  to.  The 
tubercle,  the  histologic  unit  of  the  tuberculous 
process,  is  produced  as  follows,  according  to  the 
interpretations  of  Baumgarten :  When  a  bacillus 
reaches  a  lymph  gland,  for  example,  it  multiplies 
slowly  and,  partly  through  its  presence  as  a  foreign 
body,  but  particularly  through  its  toxic  secretions, 
injures  the  surrounding  connective  tissue  and  en- 


THE     TUBERCLE.  589 

dothelial  cells  to  a  certain  degree.  Under  some 
circumstances,  especially  in  the  parenchymatous 
organs  and  lymph  glands,  this  injury  may  be  so 
great  as  to  cause  the  death  of  the  adjacent  cells 
(focal  necrosis).  When  it  is  of  a  lower  order  the 
connective  tissue  and  endothelial  cells  respond  to 
the  stimulus  by  dividing  mitotically  and  eventu- 
ally accumulate  in  large  numbers  within  a  limited 
area  surrounding  the  micro-organisms.  Not  only 
the  endothelial  cells  of  the  lymph  spaces,  but  also 
those  of  the  adjacent  blood  vessels,  take  part  in 
the  proliferation,  many  of  the  vessels  being  obliter- 
ated in  consequence.  Not  infrequently  bacilli  arc 
ingested  by  the  new  cells,  although  the  ability  of 
the  latter  to  destroy  the  organisms  is  not  clearly 
established.  Metchnikoff  says  that  tubercle  bacilli 
may  remain  intracellular  for  many  months  and, 
although  not  killed,  the  pathogenicity  is  decreased 
or  destroyed.  The  new  cells  are  of  polygonal  shape, 
are  fairly  rich  in  cytoplasm,  contain  large  vesicular 
nuclei  and  are  termed  "epithelioid"  cells. 

Certain  of  the  epithelioid  cells,  usually  those  in  ^^^^^  ceiis. 
the  center  of  the  tubercle,  where  the  bacilli  are 
most  numerous,  undergo  atypical  proliferation  in 
that  repeated  nuclear  division  takes  place  without 
corresponding  division  of  the  cytoplasm.  This 
process  results  in  the  formation  of  the  multinu- 
clear  giant  cell  which  is  so  characteristic  of  the 
well-developed  tubercle,  although  not  distinctive  of 
the  disease,  i^ccording  to  Weigert,  the  failure  of 
complete  cell  division  is  due  to  injury  to  the  cyto- 
plasm (partial  necrosis)  by  the  bacteria  which  the 
cell  contains.  Metchnikoff  and  others  take  a  dif- 
ferent view  of  the  formation  of  giant  cells,  con- 
sidering that  they  represent  individual  epithelioid 


690  INFECTION     AND     IMMUNITY. 

cells  which  have  fused  to  form  a  multinuclear 
mass. 
Retrogres-  Still  more  remote  from  the  center  of  the  tuber- 
sive  Changes.  ^^^^  ^^^^  .^^  surrounding  the  epithelioid  cells,  wan- 
dering lymphoid  and  plasmal  cells  accumulate. 
Certain  retrogressive  changes,  especially  necrosis 
and  caseation,  characterize  the  further  history  of 
the  tubercle,  although  these  changes  do  not  occur 
equally  early  nor  with  equal  intensity  in  all  cases. 
Necrosis  begins  in  the  center  of  the  lesion,  and  the 
view  is  often  expressed  that  the  formation  of  the 
giant  cell  is  the  first  indication  of  the  retrogressive 
change.  Cell  degenerations,  however,  with  karyor- 
rhexis  may  occur  before  giant  cells  have  formed. 
With  the  death  of  the  central  tissue  there  occurs 
sooner  or  later  the  death  of  many  of  the  bacilli  in 
this  portion  of  the  tubercle.  The  progressive  for- 
mation of  new  tissue  continues  in  the  periphery  as 
the  degenerative  changes  take  place  toward  the 
center;  the  tubercle  enlarges,  both  epithelioid  and 
the  surrounding  lymphoid  cells  increase  corre- 
Formation  spoudiugly,  and  new  giant  cells  form  at  the  periph- 
**'  ^T^s^s*!^!  ery  of  the  necrotic  center,  only  to  be  included  in 
the  degenerated  area  as  the  latter  extends.  In 
favorable  cases,  in  which  the  virulence  of  the  or- 
ganism is  low  or  the  resistance  of  the  individual 
strong,  the  tuberculous  area  is  eventually  sur- 
rounded by  adult  fibrous  tissue  which  in  a  sense 
accomplishes  the  isolation  of  the  infected  area. 
Without  question  such  a  capsule  of  scar  tissue  is  an 
obstacle  to  the  extension  of  the  tuberculous  proc- 
ess, whether  it  surrounds  a  nodule  in  a  lymph 
gland,  a  cold  abscess  or  a  tuberculous  sinus. 
Further  steps  in  the  healing  consist  of  caseation  of 
the  entire  area,  its  partial  or  complete  substitution 


MIXED     INFECTIONS. 


591 


by  connective  tissue  (tuberculous  scar),  or  partial 
impregnation  with  lime  salts  (calcification).  Not 
infrequently  the  caseous  portion  of  a  nodule  under- 
goes liquefaction,  which  some  have  referred  to  the 
action  of  proteolytic  ferments.  The  contents  of 
such  foci  finally  become  sterile.  In  the  event  that 
healing  of  this  nature  does  not  occur,  the  infection 
is  transmitted  to  other  organs  as  described  above. 

The  temperature,  loss  of  weight,  fever,  increased 
cardiac  action,  and  arteriosclerosis  which  are  seen 
in  tuberculosis  indicate  that  the  products  of  the 
bacillus  have  a  profound  effect  on  the  functions 
of  the  body,  and  produce  great  disturbances  in 
metabolism,  although  they  seem  to  have  no  marked 
selective  action  for  particular  tissues.  Many  dis- 
turbances are  secondary  to  changes  produced  in 
particular  organs  and  are  not  referable  to  specific 
action  of  the  toxins,  such  as  those  which  are 
consequent  on  poor  oxygenation  in  pulmonary 
tuberculosis,  and  the  amyloid  degeneration  which 
follows  prolonged  suppurative  tuberculosis. 

Mixed  infection,  especially  with  the  streptococ- 
cus, plays  a  very  important  part  in  the  course  of 
pulmonary  tuberculosis,  especially  in  the  caseous 
and  cavernous  forms.  Staphylococci,  B.  pyocya- 
neus,  various  diplococci,  the  pneumococcus,  bacil- 
lus of  Friedlander,  diphtheria  and  pseudo-diph- 
theria bacilli,  and  the  influenza  bacillus  are  also 
found  as  secondary  organisms  in  pulmonary  tuber- 
culosis. Some  of  them  invade  the  surrounding 
healthy  tissue,  cause  lobular  consolidations,  and  in 
this  way  probably  prepare  a  favorable  soil  for 
further  extension  of  the  tuberculous  process.  They 
doubtless  hasten  the  liquefaction  of  caseated  tissue, 
a  step  in  the  formation  of  abscesses.    The  high  and 


Caseation, 
Calcification 
and   Lique- 
faction. 


General  and 

Secondary 

Disturbances. 


3Iixed 
Infections. 


592  INFECTION     AND     IMMUNITY. 

irregular  fever  often  seen  in  advanced  tuberculosis 
is  commonly  septic  in  its  cause,  and  a  terminal 
streptococcus  septicemia  is  not  infrequent.  It  is 
evident  that  mixed  infections  may  complicate  at- 
tempts at  serum  therapy. 
Principles  of  The  csscntial  principles  in  the  prevention  of 
tuberculosis  consist  of,  first,  the  early  recognition 
of  the  disease,  so  that  the  patient  may  be  properly 
treated  and  cured,  if  possible,  with  the  result  that 
a  new  center  of  contagion  is  avoided;  second,  the 
rendering  of  well-developed  cases  harmless  by  suit- 
able isolation  and  proper  disposal  of  infected  ex- 
cretions; third,  the  disinfection  of  the  rooms, 
clothing,  linen  and  surroundings  of  tuberculous 
patients.  A  fourth  point,  the  prohibition  of  mar- 
riage among  the  tuberculous,  is  one  of  great  con- 
sequence, although  we  have  little  ground  to  hope 
for  its  realization.  A  fifth  point,  not  yet  fully 
established,  is  the  possibility  of  universal  vaccina- 
tion against  the  disease. 
Disposal       The  collection  of  infected  sputum  in  properly 

of   Sputum.  ^  I       r       J 

constructed  water-proof  paper  boxes,  which,  with 
their  contents,  should  be  burned  daily,  is  the  safest 
method  of  disposing  of  this  material,  and  the  moit 
effective  means  of  preventing  infection  of  the  pa- 
tient's surroundings.  Metallic,  glass  or  earthen- 
ware sputum-cups  containing  5  per  cent,  phenol 
solution  are  serviceable,  but  must  be  subjected  to 
frequent  cleansing.  When  sputum  is  collected  on 
a  handkerchief  the  latter  should  be  boiled  within 
twelve  hours  and  not  allowed  to  dry ;  that  the  hands 
of  the  patient  are  likely  to  be  contaminated  from 
the  handkerchief  is  evident.  In  coughing,  the 
handkerchief  should  be  held  to  the  mouth  to  catch 


PROPHYLAXIS.  593 

droplets  of  sputum  and  saliva  which  are  expelled. 
The  ordinances  and  rules  which  prohibit  expecto- 
ration in  street  cars  and  other  public  places  should 
be  enforced.  When  bacilli  are  discharged  in  the 
urine  and  feces  or  in  the  pus  of  tuberculous  ab- 
scesses and  sinuses,  these  secretions  should  be  dis- 
infected by  suitable  means  (chlorid  of  lime). 
Healthy  persons  should  come  in  contact  with  the 
tuberculous  as  little  as  possible,  and  the  eating 
utensils  of  the  latter  should  be  used  by  no  one  else. 

The  floor  of  a  room  which  is  inhabited  by  a  tuber-  Disinfection. 
culous  person  should  always  be  moistened  before  it 
is  swept,  in  order  to  avoid  stirring  up  the  dust. 
After  the  death  or  removal  of  a  patient,  the  entire 
surface  of  the  room  and  all  its  contents  should  be 
thoroughly  disinfected  by  appropriate  means.  The 
proper  disinfection  of  the  premises  which  were 
once  occupied  by  a  consumptive  should  be  a  legal 
requirement,  just  as  similar  procedures  are  de- 
manded in  the  case  of  smallpox  and  some  other 
contagious  diseases. 

The  special  hospital  in  which  the  indigent  tuber- 
culous may  be  properly  cared  for  and  isolated  has 
been  a  powerful  factor  in  causing  the  decrease  of 
tuberculosis  which  has  been  noted  in  many  coun- 
tries. The  removal  of  a  patient  to  such  an  institu- 
tion means  the  elimination  of  an  infected  focus 
from  the  community. 

Cold-blooded  animals  (fish,  amphibians,  rep-  ??i*.^®^*j^'fl 
tiles),  and  most  birds  are  not  highly  susceptible  to  imnmnity. 
tuberculosis,  although  special  varieties  of  the  ba- 
cillus cause  the  disease  in  certain  of  them  under 
natural  conditions.  When  tubercle  bacilli  are  in- 
jected into  the  circulation  of  birds,  they  may  re- 
main in  the  blood  and  organs  for  months,  produc- 


Racial  and 
Individual 


594  INFECTION     AND     IMMUNITY. 

ing  little  or  no  tissue  change,  although  they  retain 
their  virulence  for  other  animals  (guinea-pigs). 
Xo  animal  exceeds  the  guinea-pig  in  its  susceptibil- 
ity to  this  disease.  Goats  and  sheep  are  fairly  re- 
sistant, and  the  same  is  probably  true  of  the  horse, 
although  its  artificial  infection  is  not  diiBcult. 
That  different  varieties  of  a  species  may  vary  in 
their  susceptibility  is  illustrated  by  the  field  mouse, 
which  is  highly  susceptible,  and  the  white  mouse, 
Variations,  which  is  relatively  immune.  AltLough  similar 
variations  may  exist  among  different  races  of  men, 
they  are  not  readily  demonstrated.  The  high  sus- 
ceptibility which  appears  to  exist  among  certain 
races,  as  the  negro,  may  be  explained  in  part  by  un- 
hygienic methods  of  living,  in  which  safeguards 
against  infection  are  not  taken. 

The  discovery  of  healed  or  healing  tuberculous 
foci  in  70  to  90  per  cent,  of  all  autopsies,  in  con- 
trast to  the  15  to  20  per  cent,  of  deaths  from  tuber- 
culosis, shows  that  susceptibility  and  immunity  are 
subject  to  marked  individual  variations.  The 
ability  of  an  individual  to  overcome  a  tuberculous 
infection  is  referred  in  a  vague  way  to  an  unusual 
resistance  on  his  part;  his  defensive  powers  are 
said  to  be  strong.  Although  we  remain  to  a  large 
extent  in  the  dark  concerning  these  defensive 
powers,  they  seem  to  rest  chiefly  in  the  ability  of 
the  tissues  to  destroy  the  bacilli;  that  is,  the  re- 
sistance is  antibacterial.  Many  bacilli  may  be  de- 
stroyed by  leucocytes  or  endothelial  cells  before 
they  are  able  to  cause  tissue  changes.  It  was  stated 
previously  that  healing  in  many  instances  depends 
on  isolation  of  the  focus  by  epithelioid,  lymphoid 
and  plasma  cells,  and  by  connective  tissue.  On 
general  grounds  we  may  assume  that  a  tissue  reac- 


IMMUNITY.  595 

tion  of  this  nature  takes  place  with  greater  vigor 
and  rapidity  in  a  strong,  healthy  person  than  in 
one  of  lower  vitality.  Aside  from  the  question  of 
individual  resistance,  recovery  or  progressive  infec- 
tion may  depend  on  the  smaller  or  larger  amount 
of  bacilli  which  gained  entrance  to  the  body,  as 
well  as  on  their  virulence.  Experiments  show  that 
susceptible  animals  recover  from  minute  doses, 
whereas  tliey  succumb  to  somewhat  larger  doses  of 
bacilli. 

Various  external  influences  increase  susceptibil-  Predisposing 
ity  and  resistance.  Tuberculosis  is  to  no  small  de- 
gree a  disease  of  the  poor,  who  so  frequently  live 
in  an  undernourished  condition,  in  crowded,  dirty 
rooms,  with  little  sunlight  and  fresh  air.  The 
disease  is  more  common  in  the  city  than  in  the 
country,  where  an  outdoor  life  is  the  rule.  Alco- 
holism, diabetes,  measles,  scarlatina,  whoopin,- 
cough  often,  and  influenza  not  infrequently,  are 
precursors  of  tuberculosis.  Conditions  which  favor 
anemia,  as  pulmonary  stenosis  (rare),  predispose 
to  pulmonary  tuberculosis,  whereas  insufficiency  of 
the  left  heart,  accompanied  by  congestion  of  thn 
lungs,  is  not  often  associated  with  the  disease,  al- 
though it  has  no  influence  in  preventing  infection 
in  other  organs.  Tuberculosis  is  more  frequent 
during  the  first  two  or  three  years  of  life,  when 
children  are  so  commonly  confined,  than  from  the 
third  to  the  fifteenth  year,  when  they  live  in  the 
open  air  so  largely.  From  the  fifteenth  year  to 
middle  life  or  later  the  disease  increases  in  fre- 
quency because  of  greater  exposure  to  infection. 
Physicians  who  are  familiar  with  tuberculosis  in 
Scandinavian  countries  and  in  America  comment 


Tendency." 


596  INFECTION     AND     IMMUNITY. 

on  the  extent  to  which  tuberculosis  develops  among 
Scandinavians  after  they  come  to  this  country. 
"Hereditary  Xothin£^  is  commouei  than  the  occurrence  of 
several  successive  cases  of  phthisis  in  the  members 
of  a  family,  and  the  expression,  heard  on  all  sides, 
that  "tuberculosis  is  in  the  family,^'  indicates  the 
general  belief  that  a  family  tendency  may  be  trans- 
mitted from  generation  to  generation.  During 
recent  years,  however,  closer  analysis  of  the  condi- 
tions has  led  many  to  doubt  the  existence  or,  at  any 
rate,  the  importance  of  family  tendency  or  inher- 
ited predisposition,  and  to  refer  the  frequent  oc- 
currence of  tuberculosis  in  a  family  to  the  greater 
exposure  to  infection  which  is  occasioned  by  close 
contact  with  a  pre-existing  case.  Cornet,  who  has 
made  a  close  statistical  study  of  tuberculosis,  dis- 
credits entirely  the  hypothesis  of  hereditary  pre- 
disposition, and  Cornet  and  Meyer  refer  to  the 
"habitus  puthisicus/'  which  we  are  disposed  to 
look  on  as  an  objective  evidence  of  hereditary  ten- 
dency, as  a  result  rather  than  a  cause  of  pulmonary 
tuberculosis.  It  is  fair  to  say  that  the  development 
of  tuberculosis  in  several  members  of  a  family  is 
not  prima  facie  evidence  of  the  existence  of  a 
family  predisposition  for  the  disease.  Where  thero 
are  tubercle  bacilli  there  is  likely  to  be  tuberculosis, 
and  the  occurrence  of  the  infection  in  one  fur- 
nishes the  prerequisite,  that  is,  bacilli,  for  the  de- 
velopment of  the  disease  in  other  members  of  the 
family.  It  is  probable  that  the  verdict  of  family 
tendency  has  often  been  pronounced  erroneously. 
At  present,  however,  we  may  not  be  justified  in 
considering  the  subject  a  closed  chapter. 

It  is  the  commcnly  accepted  opinion  that  recov- 
ery from  tuljrculosis  does  not  confer  immunity  to 


IMMUNITY.  597 

subsequent  attacks.  Cornet  and  Meyer  suggest  as  Acanired 
an  explanation  of  this  condition  that  the  local  le- 
sion is  so  strictly  isolated  that  a  sufiBcient  amount 
of  toxin  does  not  escape  into  the  circulation  to 
cause  a  general  reaction,  hence  the  formation  of  an- 
titoxin or  other  antibodies  is  impossible.  This  ex- 
planation seems  inadequate,  however,  when  we  re- 
member the  strong  antitoxic  immunity  which  de- 
velops in  tetanus  and  diphtheria  in  spite  of  the  lo- 
calization of  the  bacteria.  The  results  of  artificial 
immunization,  in  which  unlimited  amounts  of 
toxic  material  or  bacilli  may  be  injected  without 
the  formation  of  satisfactory  antitoxins,  seem  to 
indicate  that  the  toxic  constituents  of  the  tubercle 
bacillus  lack  the  power  of  causing  the  formation  of 
a  strong  antitoxin. 

In  opposition  to  the  prevailing  opinion,  certain 
observers  find  ground  for  the  belief  that  recovery 
from  local  tuberculosis  of  the  lymph  glands,  skin  or 
bones,  actually  does  render  the  patients  immune  to 
pulmonary  consumption  (Maragliano  and  others). 
In  early  experiments  Koch  noted  that  when  tuber- 
cle bacilli  were  injected  subcutaneously  into 
guinea-pigs  which  were  suffering  from  general  tu- 
berculosis, the  subcutaneous  inoculation  remained 
as  a  local  infection  and  not  infrequently  healed 
after  sloughing.  The  general  infection  would  seem 
to  have  increased  local  resistance.  Although  other 
investigators  failed  to  duplicate  the  observation  of 
Koch,  this  result  is  said  to  have  suggested  to  him 
the  idea  of  active  immunization  as  a  cure  for  tu- 
berculosis, a  method  subsequently  practiced  by 
treatment  with  the  various  tuberculins. 

In  the  United  States,  Trudeau  and  de  Schwein- 
itz,   and  in  Europe,   Koch,  Behring,   Maragliano 


598  lyFECTWS     AND     IMMUNITY. 

Active  im-  and  Baumgarten,  with  their  followers,  have  prac- 
ticed assiduously  the  artificial  immunization  of 
animals  with  the  tubercle  bacillus  or  various  prep- 
arations from  the  organism,  with  the  hope  of  pro- 
ducing active  immunity  to  the  disease.  Williams, 
Webb  and  Barber  have  successfully  immunized 
animals  by  the  injection  of  living  virulent  tubercle 
bacilli  into  the  subcutaneous  tissue.  In  these 
experiments,  the  immunization  was  begun  with  a 
single  isolated  tubercle  bacillus  as  the  first  dose. 
The  immunity  was  demonstrated  by  the  fact  that 
the  animals  were  able  to  withstand  the  injection  of 
many  times  the  fatal  dose  of  living  tubercle  bacilli. 
The  indications  are  that  in  preparation  of  tubercle 
bacillus  vaccines  by  heat,  etc.,  the  antigenic  prop- 
erties of  the  bacilli  are  unfavorably  modified.  Rel- 
atively avirulent  strains  as  those  cultivated  from 
fish,  turtle  or  fowls,  have  been  utilized  for  the  first 
injections.  As  immunization  progresses  one  of  two 
processes  may  be  followed:  either  the  quantity  in- 
jected may  be  increased  gradually,  as  when  killed 
or  avirulent  bacilli  are  used,  or  the  immunization 
having  been  begun  with  avirulent  living  cultures 
those  of  higher  virulence  may  be  substituted  later. 
In  any  case  immunization  is  difficult  and  slow, 
and  many  animals  may  be  lost  from  cachexia  or 
from  tuberculosis  which  develops  from  hasty  pro- 
gression in  dosage.  The  subcutaneous  injection 
of  intact  cells  has  the  disadvantage  that  local  ab- 
scesses frequently  develop,  and  to  avoid  this  the 
intravenous  injection  of  smaller  doses  has  been 
practiced  in  some  instances.  For  active  immuniza- 
tion the  "new  tuberculin"  of  Koch  containing  all 
the  cellular  constituents  in  a  finely  divided  form 
has  the  advantages  that  it  may  be  given  subcu- 


in  DiagnosiM. 


DIAGNOSIS.  599 

ianeously  without  abscess  formation  and  is  ab- 
sorbed with  some  rapidity.  An  animal  or  person 
immunized  with  TR  is  immune  to  all  the  constitu- 
ents of  the  bacillus.  The  condition  produced  by 
active  immunization  is  one  of  increased  resistance 
rather  than  of  absolute  immunity;  large  doses  of 
bacilli  may  cause  infection.  The  nature  of  the 
new  resistance  is  not  satisfactorily  established. 

Inasmuch  as  tuberculin  is  used  not  only  for  Tuberculin 
diagnosis  but  also  for  curative  purposes  in  man 
(active  immunization),  and  since  the  principles  of 
action  are  similar  in  both  instances,  the  use  of 
tuberculin  may  be  considered  at  this  point.  A 
healthy  man  is  not  susceptible  to  moderate  doses, 
but  a  tuberculous  man  is  even  more  susceptible 
to  the  toxin  than  the  tuberculous  guinea-pig, 
since  1  mg.  often  causes  an  intense  reaction. 
Weigert  classifies  the  disturbance  which  tuber- 
culin may  produce  in  the  tuberculous  as  thermal, 
circulatory,  respiratory,  digestive,  nervous  and 
vasomotor,  and  secretory.  Necrosis  may  be  pro- 
duced at  the  point  of  injection.  In  so  far  as  the  di- 
agnostic use  of  tuberculin  is  concerned,  we  are  in- 
terested chiefly  in  the  thermal  disturbances, 
which  are  accompanied  by  chills,  malaise  and 
muscular  pains.  Following  injection  of  a  suitable 
quantity,  a  period  of  incubation  of  from  eight  to 
fourteen  hours  follows,  and  at  the  end  of  this  time 
the  temperature  rises  progressively  for  two  or 
more  hours  and  may  reach  a  maximum  of  from  40° 
to  41°  C;  after  remaining  at  this  point  for  from 
two  to  six  hours,  it  recedes  rapidly.  In  addition 
to  this  general  reaction,  the  toxin  causes  conges- 
tion, redness  and  swelling  at  tne  site  of  the  tuber- 
culous lesions,  i.  e.,  the  foci  become  surrounded  by 


600  INFECTION     AND     IMMUNITY. 

an  inflammatory  reaction.  This  is  seen  most 
readil}^  in  the  tubercles  of  lupus  vulgaris,  and  in 
the  lungs  declares  itself  by  an  increase  in  rales 
and  expectoration,  caused  by  the  exudation  ac- 
companying the  inflammatory  reaction. 

For  diagnostic  purposes  the  technic  of  adminis- 
tration is  as  follows:     It  must  first  be  assured 

*  that  the  patient  has  no  continued  fever  by  noting 

the  temperature  every  two  hours  for  several  days. 
One  milligram  of  tuberculin  is  injected  subcu- 
taneously,  this  amount  being  obtained  by  suitable 
dilution  of  the  original  solution.  It  is  often  advis- 
able in  weak  or  young  subjects  to  use  0.05  or  0.1 
mo^.  Manv  authorities  never  exceed  0.1  mof.  as  an 
initial  dose.  If  no  rise  in  temperature  is  produced 
by  this  amount,  a  second  injection  of  a  larger 
quantity  may  be  given  after  an  interval  of  two  or 
three  days.  Koch  used  as  high  as  10  mg.  before 
concluding  that  the  reaction  is  negative.  Lowen- 
stein  and  others  recommend  the  cumulative  action 
of  three  or  four  small  doses  of  tuberculin  (0.1  to 
0.5  mg.)  at  intervals  of  three  days.  The  advan- 
tage of  this  method  is  due  to  the  fact  that  the 
diagnostic  value  of  a  reaction  with  a  small  dose 
of  tuberculin  exceeds  the  value  of  reactions  with 
large  doses.  By  this  method,  many  patients  are 
said  to  react  with  the  first  small  dose  while  the 
cumulative  action  of  subsequent  doses  results  in 
a  reaction  in  less  susceptible  individuals. 
Theories  of       Koch  explained  the  tuberculin  reaction  by  the 

ii*n  Rea^uon'  harmful  or  necrotic  effect  on  the  leucocytes  and 
other  tissue  cells.  The  substances  formed  by  the 
breaking  down  of  these  cells  give  rise  to  the  fever 
and  other  symptoms.  In  tuberculous  tissues  this 
effect  of  tuberculin  is  much  more  marked. 


Tuberculin. 


DIAGNOSIS.  601 

Babes  supposed  that  the  increased  susceptibility 
of  tuberculous  persons  was  due  to  a  summation 
of  effects  of  the  products  of  the  tubercle  bacilli 
in  the  tuberculous  focus  and  the  injected  tuber- 
culin. Von  Pirquet  and  Schick  explain  the  tuber- 
culin reaction  as  a  phenomenon  of  allergy.  This 
explanation  is  the  most  satisfactory  one.  (See 
Allergy.) 

In   view   of   Naegeli's   finding  of   tuberculosis,  i.imitations 
healed  or  active,  in  97  per  cent,  of  autopsies,  the  use  of 
value  of  the  tuberculin  reaction  would  seem  to  be 
a  relative  one,  and  that  the  number  of  positive 
reactions  obtained  would  depend  on  the  amount  of 
tuberculin  used. 

Experience  has  taught  certain  limitations  to  the 
diagnostic  value  of  tuberculin:  1.  The  test  can 
not  be  applied  to  febrile  cases  inasmuch  as  the 
pre-existing  fever  could  not  be  separated  from  that 
which  the  tuberculin  might  produce.  2.  Cases  of 
advanced  tuberculosis  frequently  fail  to  give  the 
reaction.  The  tissues  of  such  patients  have  be- 
come resistant  to  the  poison.  3.  It  is  said  that 
tuberculin  frequently  causes  a  similar  reaction  in 
those  suffering  from  leprosy,  actinomycosis  and 
syphilis.  Cornet  and  Meyer  suggest  that  the 
phenomenon  as  it  occurs  in  leprosy  and  actinomy- 
cosis is  to  be  considered  in  the  nature  of  a  "group 
reaction^'  in  view  of  the  close  relationship  of  the 
tubercle  bacillus  to  actinomyces  and  Bacillus  leprcB. 
It  does  not  always  occur  in  syphilis,  and  in  posi- 
tive cases  a  latent  tuberculosis  may  be  responsible 
for  the  reaction.  By  a  number  of  writers  the  facts 
just  stated  are  taken  to  indicate  that  the  reaction  is 
not  of  specific  character;  that  it  may  often  be  ob- 
tained in  the  tuberculous  by  the  injection  of  ap- 


602  INFECTION     AND     IMMUNITY. 

parently  indifferent  substances  as  trypsin,  peptone 
(albumose),  sodium  cinnamate  and  the  "mycopro- 
teins"  of  other  bacteria  provides  additional  sup- 
port to  this  view.  On  the  other  hand,  since  rela- 
tively large  amounts  of  these  indifferent  sub- 
stances are  required  to  produce  the  reaction,  where- 
as minute  amounts  of  tuberculin  suffice,  others 
hold  that  the  specificity  of  the  latter  substance 
may  be  maintained. 

Earlv  tuberculosis  reacts  to  tuberculin  in  the 
most  typical  manner.  On  account  of  the  fact  that 
latent  or  healing  cases  may  respond  to  the  test,  its 
positive  outcome  gives  no  indication  of  the  serious- 
ness of  the  patient's  condition,  which  is  a  practical 
question  of  some  importance. 
uanser  (?»  The  fcar  that  tuberculin,  in  producing  an  in- 
Tubercuiin.  flammatory  reaction  around  tuberculous  areas, 
may  cause  a  dissemination  of  the  bacilli,  has  acted 
strongly  in  preventing  the  use  of  the  toxin  for 
both  diagnostic  and  therapeutic  purposes.  On  a 
priori  grounds,  such  an  event  would  seem  to  be  a 
possibilit}^,  for,  with  the  inflammation,  the  vessels 
surrounding  the  tubercles  become  congested,  new 
leucocytes  accumulate  and  there  is  an  extravasation 
of  fluid.  Since  during  the  subsidence  of  the  in- 
flammation a  certain  number  of  leucocytes  may 
again  leave  the  area  and  as  the  extravasated  fluid 
returns  to  the  circulation,  bacilli  may  be  carried  to 
other  tissues  by  them.  Contrary  to  such  reasoning, 
however,  the  observations  of  Koch  and  his  follow- 
ers in  animal  experiments  and  in  the  diagnostic 
and  therapeutic  use  of  tuberculin  in  man,  lead 
them  to  say  that  tuberculin  when  properly  ad- 
ministered never  causes  an  aggravation  or  exten- 
sion   of   the    disease.      Similar   conclusions    were 


FIRQUET     REACTION.  603 

reached  by  Trudeau,  Baldwin  and  Kinghorn  in 
animal  experiments  in  which,  "as  in  previous  ob- 
servations, a  favorable  absorptive  influence  was 
noted  on  the  diseased  focus."  Bearing  in  mind 
the  limitations  mentioned  above,  and  the  possibil- 
ity of  the  reaction  being  induced  by  leprosy,  acti- 
nomycosis and  syphilis  (  ?),  the  statement  of  Osier 
may  be  quoted  that  "in  obscure  internal  lesions, 
in  joint  cases  and  in  suspected  tuberculosis  of  the 
kidneys 'the  use  of  tuberculin  gives  most  valuable 
information.'^ 

Yon  Pirquet  made  use  of  the  increased  capa-  cutaneous 

,  .,.  _     ,  ,  .  p  I'll  ,     Reaction  of 

bility  of  the  skin  oi  tuberculous  patients  to  react  v.  pirqnet. 
to  tuberculin  as  a  means  of  diagnosis  of  tuber- 
culosis (see  Anaphylaxis).  The  test  is  carried  out 
as  follows :  The  ventral  surface  of  the  forearm  is 
cleansed  with  ether  and  two  drops  of  old  tuber- 
culin are  placed  on  the  skin  at  points  about  10  cm. 
apart.  The  skin  underneath  the  tuberculin  is 
then  scarified  over  an  area  about  the  size  of  a  pin- 
head,  as  for  an  ordinary  small-pox  vaccination.  A 
small  quantity  of  cotton  is  then  placed  over  the 
scarifications  until  they  are  dry.  A  third  scarifi- 
cation is  made  about  10  cm.  from  one  of  the  first 
two  and  no  tuberculin  used.  This  is  to  be  used 
as  a  control. 

The  ensuino-  reactions  are  described  bv  v.  Pir- 
quet  as  follows: 

1.  Traumatic  reaction:  The  vaccination  and 
control  sites  show  in  a  few  minutes  a  small  papule 
surrounded  by  a  soft  red  areola  which  disappears 
in  a  few  hours.  There  remains  a  small  slightly 
raised  pinhead-sized  red  spot  which  becomes  cov- 
ered with  a  crust.    This  is  succeeded  by  pigmenta- 


604  INFECTION     AND     IMMUNITY. 

tion  and  then  a  gradual  return  to  normal  within 
a  week  or  two. 

2.  Negative  reactions  show  the  same  phenomena 
as  the  control  site.  The  swelling  lasts  only 
twenty-four  hours,  and  the  areola  is  under  5  mm. 
in  diameter. 

3.  The  positive  reaction:  (a)  Incubation  period, 
which  lasts  from  three  to  twenty-four  hours.  In 
most  cases  the  reaction  is  fully  developed  in 
twenty-four  hours.  Those  developing  later  than 
twenty-four  hours  v.  Pirquet  calls  "torpid."  These 
torpid  reactions  occur  more  frequently  in  older 
than  in  young  children  and  in  clinically  unsus- 
pected cases.  It  occurs  in  manifest  tuberculosis 
only  exceptionally. 

(b)  Development:  The  inflammatory  reaction 
begins  usually  with  a  slightly  raised  areolar  red- 
dening which  spreads  from  the  scarification  site 
and  increases  rapidly  in  diameter  and  height.  The 
diameter  of  the  papule  is  on  an  average  about  1 
cm.  but  may  reach  3  cm.  Small  vesicles  may  form 
on  the  surface  of  the  papule.  The  color  differs 
with  the  normal  coloring  of  the  skin;  usually  it 
is  of  a  deep  red  color.  Very  pale  papules  some- 
times develop  in  cases  of  fatal  tuberculosis  (cach- 
ectic reaction).  The  border  of  the  papule  is  some- 
times sharp,  sometimes  irregular  and  at  times 
small  papules  may  be  found  surrounding  it. 

(c)  Eetrogression.  The  maximum  development 
is  usually  reached  in  forty-eight  hours  and  after 
this  the  swelling  declines  and  the  red  color  changes 
to  a  violet,  then  to  a  yellow  color  and  finally 
becomes  brown.  The  swelling  disappears  usually 
in  from  five  to  eight  days  and  the  pigmentation 


PIRQUET    REACTION. 


605 


in  a  few  weeks.  The  best  time  for  a  single  obser- 
vation is  48  hours  after  the  vaccination. 

(d)  Secondar}'  reaction :  In  cases  giving  a  neg- 
ative reaction  a  second  test  may  be  followed  by  a 
positive  reaction.  In  this  case,  the  first  vaccina- 
tion site  may  show  a  slight  reddening. 

The  cutaneous  reaction  is  a  very  delicate  one  yaiue  of  ^ 

.         .  .      th.e  Reactio 

and  many  cases  of  healed  tuberculosis  give  a  posi- 
tive reaction.  Since  most  adults,  according  to 
autopsy  findings,  have  healed  foci  of  tuberculosis 
the  reaction  as  an  indication  of  active  lesions  is 
of  value  only  in  children  below  the  age  of  puberty. 

Various  modifications  of  the  v.  Pirquet  reaction 
have  been  devised  but  cannot  be  discussed  here. 

Calmette  proposed  the  instillation  of  tuberculin  Q^^J^i^aimic 
into  the  conjunctival  sac  as  a  diagnostic  procedure  Reaction. 
in  tuberculosis.  In  negative  cases  this  is  followed 
by  only  a  slight  reddening.  In  positive  reactions 
a  more  or  less  severe  conjunctivitis  follows.  The 
reaction  has  not  become  popular  owing  to  the  pos- 
sibility of  danger  to  the  eye. 

The  original  unfavorable  results  which  were  ob- 
tained in  the  therapeutic  administration  of  tuber- 
culin are  referred  by  Koch,  Petruschky  and  others 
to  improper  selection  of  patients.  Those  in  a  feb- 
rile condition  and  those  in  whom  destruction  of 
tissue  is  advanced  are  not  suited  for  the  treatment, 
and  in  them  little  or  nothing  is  to  be  hoped  from 
the  administration  of  tuberculin.  Its  curative  value 
is  supposed  to  depend  on  the  local  inflammatory 
reaction  which  it  causes  around  tuberculous  foci, 
and  perhaps  also  on  the  necrosis  which  Koch  claims 
is  caused  in  the  tubercles  themselves.  It  must  be  the 
object  during  the  whole  course  of  treatment  to  ad- 
minister the  toxin  in  such  doses  that  a  moderate 


Ttiljerctiliii 
Tlierapy. 


G06  INFECTION     AND     IMMUNITY. 

or  minim-um  local  reaction  occurs.  Larger  amounts 
which  would  cause  febrile  reactions  and  eventually 
render  the  patient  resistant  to  tuberculin  and  thus 
preclude  the  local  changes  are  to  be  avoided.  It  is 
customary  to  begin  with  0.1  to  0.05  milligrams 
and  gradually  to  increase  the  amount  injected. 
If  fever  is  caused  by  a  particular  dose,  larger 
amounts  are  not  to  be  given  until  fever  ceases  to 
follow  this  dose.  By  th-e  time  a  dosage  of  50  milli- 
grams is  reached,  which  may  require  many  months, 
the  patient  usually  has  lost  the  power  of  reacting 
and  the  injections  are  to  be  interrupted  until  Le 
again  becomes  sensitive  to  the  toxin  (from  thvee 
to  six  months),  after  which  treatment  should  be 
resumed.  Cure  is  recognized  when  the  patient  h^i 
lost  permanently  the  power  to  react,  his  condition 
then  being  identical  with  that  of  the  healthy  man. 

The  principles  on  which  the  action  of  tuberculin 
depend  are  hypothetical.  Marmorek  says  that  the 
fever  and  local  changes  are  due  to  a  special  toxin 
(the  true  toxin),  which  the  bacillus  secretes  under 
the  stimulation  of  the  tuberculin.  Ehrlich  sup- 
poses that  cells  adjacent  to  the  tubercles  have  been 
injured  moderately  by  the  tuberculin  which  is  pro- 
duced in  situ,  and  that  as  a  consequence  of  this 
injury  such  cells  are  particularly  susceptible  to  the 
additional  tuberculin  which  is  injected,  and  react 
to  the  stimulus  by  proliferation  (Marx).  In  ac- 
cordance with  this  conception  the  fever  also  in 
some  obscure  way  is  related  to  the  local  reaction. 

It  is  probable  that  the  therapeutic  value  of 
tuberculin  depends  on  the  utilization  of  the  sub- 
cutaneous and  other  body  cells  as  a  source  of  anti- 
bodies. The  formation  of  these  antibodies  follows 
the  injection  of  tuberculin,  whereas  in  the  tuber- 


Tuberculin." 


TUBERCULIN     TREATMENT.  607 

euloiis  process  only  the  tissues  directly  involved 
are  stimulated  to  antibody  production.  Koch  pub- 
lished favorable  results  from  the  use  of  tuberculin 
but  reports  from  other  sources  were  less  satisfac- 
tory. Koch's  NeutubercuUn  (Bazillenemulsion) 
is  used  in  a  similar  manner.  Koch  proposes  to  use  ^^f^*™"* 
the  agglutinating  power  of  the  patient's  serum  as  and  "Xew 
an  index  of  the  immunity  caused  by  the  injection. 
The  formation  of  agglutinins  perhaps  indicates  in 
a  general  way  the  ability  of  the  patient  to  form 
antibodies,  but  from  the  well-known  fact  that  the 
agglutinating  power  does  not  go  hand  in  hand  with 
the  protective  power  of  serum  in  relation  to  many 
infections,  this  method  of  estimating  the  degree 
of  immunity  does  not  rest  on  a  good  basis.  The 
agglutination  reaction  is  carried  on  with  the  emul- 
sion which  is  used  for  immunization.  Treatment 
in  man  is  begun  by  the  injection  of  0.0025  mg.  of 
solid  substance  and  the  amount  is  increased  rap- 
idly every  day  or  two  until  a  reaction  occurs  with 
a  temperature  of  from  1.5°  to  2°  C.  After  a  pause 
of  a  week  the  injections  are  begun  again  and  event- 
ually a  dose  of  20  mg.  may  be  given.  During 
treatment  the  agglutinating  power  of  the  patient's 
serum  is  tested  frequently,  and  if  it  is  not  suffi- 
ciently high  intravenous  injection  of  the  fluid  por- 
tion of  the  emulsion  may  be  practiced.  The  agglu- 
tinating power  may  go  as  high  as  from  1  to  25  to 
1  to  150,  rarely  1  to  21)0  or  300. 

Following  the  work  of  Wright  and  Douglas,  the 
opsonic  index  has  been  used  as  a  guide  to  the 
injection  of  preparations  of  tubercle  bacilli.  By 
the  concentration  of  opsonins  the  state  of  immu- 
nity can  be  gaged  and  the  dosage  thus  regulated 
as  to  time  and  amount.     By  means  of  this  proce- 


Maragrliano. 


608  INFECTION     AND     IMMUNITY. 

dure  nmch  valuable  information  has  been  obtained 
in  regard  to  the  avoidance  of  injections  during  the 
^^negative  phase"  and  the  regulation  of  the  size  of 
the  doses. 

It  is  still  a  disputed  question  as  to  whether 
the  condition  of  the  patient  as  an  indication  for 
tuberculin  injection  can  best  be  judged  by  the 
clinical  symptoms  or  by  the  estimation  of  the 
opsonic  index.  There  is  no  question,  however, 
but  that  in  suitable  cases  the  proper  application  of 
vaccine  treatment  in  tuberculosis  is  a  valuable 
therapeutic  aid. 
Serum  of  Maragliano  publishes  the  following  conclusions : 
(1)  "It  is  possible  to  produce  a  specific  (serum) 
therapy  for  tuberculosis;  (2)  It  is  possible  to 
immunize  the  animal  organism  against  tuberculo- 
sis as  is  done  in  other  infectious  diseases,  and 
there  is  good  reason  for  hope  for  an  antitubercu- 
losis vaccination  for  man."  He  recognizes  bacteri- 
cidal, antitoxic  and  agglutinating  properties  of  the 
serum  as  normal  defensive  powers  of  the  body,  and 
says  that  these  powers  are  increased  as  the  result 
of  immunization.  The  bactericidal  power  of  the 
serum  is  determined  by  its  ability  to  inhibit  the 
growth  of  cultures  of  the  tubercle  bacillus;  its 
antitoxic  power  by  its  ability  to  neutralize  a  test 
poison  which  is  obtained  from  cultures  by  macerat- 
ing them  in  hot  water;  and  its  agglutinating 
power  is  tested  with  the  homogeneous  cultures  of 
Courmont  and  Arloing.  For  the  immunization  of 
animals  a  soluble  toxin  prepared  by  the  filtration 
of  young  cultures,  and  also  the  intracellular  toxins 
which  are  extracted  by  water  from  killed  virulent 
bacilli,  are  injected.     By  using  both  substances, 


ANTITUBERCULOSIS     SERUM.  609 

antitoxic  and  other  antibodies  are  said  to  be 
formed. 

The  unusual  claim  is  made  by  Maragliano  that 
his  antituberculosis  serum  is  effective  in  the  treat- 
ment of  human  tuberculosis  not  only  because  of  its 
own  properties,  but  because  it  causes  the  tissues  to 
form  additional  antibodies.  It  is  difficult  to  take 
the  latter  claim  seriously,  since  it  is  not  in  accord 
with  the  laws  of  antibody  formation  as  we  under- 
stand them  at  the  present  time.  However,  favor- 
able reports  of  the  value  of  the  serum  have  been 
published  principally  from  Italian  sources.  It  is 
claimed  that  the  serum  manifests  its  curative  pow- 
ers and  causes  an  increase  in  specific  antibodies 
when  given  per  os. 

Maragliano  also  advocates  a  method  of  mixed   Mixed  immn- 

T  .         .  ....  .  1   •    1      iasation  and 

active  and  passive  immunization  m  man,  m  which  vaccination. 
1  c.c.  of  serum  is  given  subcutaneously  every  sec- 
ond day  for  twenty  days;  for  a  second  period  the 
same  quantity  of  serum  is  given,  but  supplemented 
by  increasing  amounts  of  the  toxic  extract  of 
bacilli ;  and  for  a  third  period  the  toxic  extract 
is  injected  in  increasing  doses  during  from  three 
to  four  months. 

The  same  authority  thinks  that  it  may  be 
possible  to  vaccinate  against  tuberculosis  by  a 
single  subcutaneous  injection  of  a  vaccine  (killed 
bacilli?).  He  states  that  in  both  man  and  animals 
antibodies  are  formed  in  the  serum  following  the 
vaccination,  and  that  in  animals  their  resistance  to 
infections  with  living  bacilli  is  increased.  Mar- 
morek  asserts  that  killed  tubercle  bacilli  which 
have  been  treated  with  his  antitoxic  serum  are 
readily  absorbed  from  the  subcutaneous  tissue,  and 
proposes  the  use  of  such  bacilli  as  a  vaccine. 


610  IXFECTION     AXD     IMMUNITY. 

Serum  of       As  stated  above,  Marniorek  discredits  tuberculin 


Marmore  -.  ^^  ^^^  spccific  toxin  of  the  bacillus.  His  "true" 
toxin  is  prepared  by  growing  young  and  virulent 
bacilli  ("primitive''  bacilli)  in  a  medium  which 
contains  leucotoxic  serum,  liver  extract,  glycerin 
and  bouillon.  The  leucotoxic  serum  is  prepared 
by  immunizing  calves  with  the  leucocytes  of 
guinea-pigs.  Theoretical  considerations  which  we 
need  not  detail  suggested  the  use  of  this  medium. 
The  cultures  are  filtered  after  a  few  days  of  growth 
and  the  formation  of  tuberculin  is  avoided  as  much 
as  possible.  The  immunization  of  horses  with  this 
filtered  toxin  yields  the  antitoxic  serum  of  Mar- 
morek.  Conflicting  reports  concerning  its  value 
are  published  from  French  sources.  Schwartz  an- 
nounces the  complete  cure  of  a  case  of  tuberculosis 
of  the  larynx,  and  another  of  virulent  tuberculosis 
of  the  conjunctiva  and  cornea  by  the  exclusive  use 
of  Marmorek's  serum. 

immiiniza-  Botli  Maragliauo  and  Behring  affirm  that  the 
*  Milk,  immunizing  substances  are  excreted  in  the  milk  of 
cows  which  have  been  strongly  immunized  against 
tuberculosis,  and  both  have  suggested  that  the  use 
of  such  milk  by  infants  may  render  them  more  re- 
sistant to  tuberculosis. 

The  agglutination  reaction  has  been  suggested 
by  Courmont  and  Arloing  and  others  as  a  means  of 
diagnosis  in  tuberculosis.  Others  who  criticise  this 
idea  affirm  that  agglutinins  are  not  developed  suf- 
ficiently in  tuberculosis  to  render  the  test  of 
value,  and  that  the  serum  of  normal  man  may  be 
as  highly  agglutinating  as  that  of  the  tuberculous. 
In  view  of  the  fact  that  the  tubercle  bacillus  grows 
in  coherent  masses  in  ordinary  cultures  special 
manipulations  are  necessary  to  render  it  suitable 


BOVINE     TUBERCULOSIS.  611 

for  the  agglutination  reaction.  Courmont  and  Ar- 
loing  prepare  a  homogeneous  culture  by  first  grow- 
ing the  organism  on  a  certain  potato  medium  and 
then  in  glycerin  bouillon,  which  is  frequently 
shaken.  The  cells  are  said  to  be  well  isolated  after 
this  procedure.  Koch  uses  his  emulsion  of  pow- 
dered bacilli  for  the  test.  The  serum  of  man  or 
animals  as  a  result  of  immunization  may  reach  an 
agglutinating  pow^r  of  1  to  2,000  exceptionally 
(Maragliano). 

APPENDIX  TO  TUBERCULOSIS. 

TUBERCULOSIS    AND    PSEUDOTUBERCULOSIS    IN    ANIMALS. 

Certain  differences  between  the  bacilli  of  human  and   BoA-ine 
bovine    tuberculosis    were    mentioned    in    the    preceding    TnberculosiB. 

section.  In  cattle  the  disease  shows  a  characteristic 
tendency  to  remain  localized  in  one  organ  or  group  of 
organs  over  a  long  period.  It  is  a  nodular  disease  as  in 
man.  but  differs  from  human  tuberculosis  in  that  no- 
dules often  grow  to  large  size,  may  be  imbedded  in  and 
sharply  differentiated  from  surrounding  healthy  tissue, 
and  not  infrequently  involve  serous  surfaces,  forming 
large  masses  of  firm  sessile  or  pedunculated  tumors. 
The  nodules  frequently  are  fibrous  from  the  beginning, 
undergo  early  and  extensive  calcification  and  rarely 
soften.  We  are  not  to  understand,  however,  that  miliary 
tuberculosis  does  not  occur  in  cattle.  Although  the 
process  in  the  lungs  is  usually  of  a  fibrous  and  large 
nodular  nature,  rapid  dissemination  with  formation  of 
many  miliary  tubercles  may  cause  the  picture  of  acute 
tuberculous  consolidation  in  a  certain  number  of  cases. 
According  to  the  statistics  of  Ostertag,  based  on  43,000 
cases  of  bovine  tuberculosis,  localization  is  as  follows: 
Lungs,  75  per  cent. ;  pleura  and  peritoneum,  50  per 
cent.;  peribronchial  glands,  60  per  cent.;  spleen,  40  per 
cent.  In  more  or  less  generalized  cases  the  lungs  are  in- 
volved in  100  per  cent,  of  the  cases;  serous  membranes,. 
90  per  cent. ;  liver,  85  per  cent. ;  digestive  tract,  GO  per 
cent. ;  spleen,  50  per  cent. ;  kidneys,  30  per  cent. ;  mouth 
cavity,  5  per  cent.  In  cows  the  uterus,  in  general  infec- 
tion, is  involved  in  65  per  cent,  of  the  cases,  the  udders 
in  from  5  to  10  per  cent.,  and  the  ovaries  in  5  per  cent. 
It  seems  that  the  lungs  are  the  most  common  infection 


612  INFECTION     AND     IMMUNITY. 

atrium,  and  transmission  probably  is  accomplished  chief- 
ly through  the  secretions  of  the  respiratory  passages. 
In  the  udders  the  process  may  at  first  be  one  of  miliary 
tuberculosis,  but  a  large  amount  of  fibrous  tissue  forms 
in  time,  many  acini  are  transformed  into  retention  cysts, 
in  which  tubercle  bacilli,  free  or  intracellular,  may  be 
present  in  large  numbers. 

Aside  from  anatomic  changes  and  clinical  symptoms, 
diagnosis  depends  on  the  tuberculin  reaction,  and,  in 
relation  to  the  udder,  the  demonstration  of  bacilli  in  the 
milk  by  staining  methods  or  inoculation  into  guinea- 
pigs. 

The  tuberculin  reaction  in  cattle  is  similar  to  that  in 
man  and  is  subject  to  the  same  general  limitations,  but 
is  used  extensively  with  the  most  satisfactory  results. 
The  complete  elimination  of  tuberculosis  from  herds  of 
cattle  is  possible,  by  using  tuberculin  as  a  diagnostic 
test,  the  slaughtering  of  infected  animals,  and  the  dis- 
infection of  stalls. 

Tuberculosis  among  sheep  and  goats  is  rare.  It  occurs 
occasionally  in  the  horse,  hog  and  dog,  and  with  more 
frequency  in  the  cat. 
A-vlan  "^  form  of  tuberculosis  is  very  common  in  the  chicken. 
Tuberculosis,  and  attacks  also  the  pheasant,  dove  and  turkey.  The 
duck  and  goose  are  exempt  from  it.  Although  the  or- 
ganism resembles  that  of  human  tuberculosis  in  size, 
staining  properties  and  other  general  characteristics, 
difi'erentiation  is  accomplished  by  means  of  the  follow- 
ing points:  1.  The  avian  bacillus  shows  a  greater  tend- 
ency to  pleoraorphinism  as  shown  by  club-shaped  forms, 
unstained  vacuoles,  "spore-like"  bodies,  and  branching 
threads.  2.  It  has  a  greater  affinity  for  aqueous  anilin 
dyes.  3.  Growth  takes  place  in  artificial  media  more 
rapidly  and  on  solid  surfaces  is  characterized  by  its 
moist  appearance  and  mucus-like  consistence  in  contrast 
to  the  dry,  warty,  brittle  growth  of  the  human  bacillus. 
4.  The  optimum  temperature  for  growth  (from  40°  to  45" 
C. )  is  several  degrees  higher  than  that  of  the  mamma- 
lian organism.  5.  Its  pathogenicity  for  guinea-pigs  is 
less  and  for  rabbits  greater  than  that  of  the  human  and 
bovine  bacilli.  Their  diff"erence  in  pathogenicity  is 
further  shown  by  the  difficulty  which  is  met  in  trying  to 
infect  fowls  with  the  human  bacillus.  By  varying  the 
conditions  of  cultivation  and  by  animal  passage  the  two 
may  be  made  to  resemble  each  other  very  closely,  al- 
though the  permanent  transformation  of  the  human  into 
the  avian,  or  vice  versa,  has  not  been  accomplished. 


TUBERCULOSIS     OF     FISH,     ETC.  613 

The  disease  attacks  especially  the  intestines,  mesen- 
tery and  liver,  in  which  are  found  hard,  yellowish-white 
nodules,  often  rich  in  lime  salts,  and  vaiying  in  size 
from  that  of  a  pea  to  that  of  a  walnut.  These  condi- 
tions suggest  the  intestines  as  the  infection  atrium.  The 
foci  are  rich  in  bacilli  and  histologically  show  the  es- 
sential characteristics  of  tuberculosis. 

"Bacillus  tuberculosis  pisciuni"  is  the  name  given  to  Tuberculosis 
an  acid-fast  organism  resembling  the  tubercle  bacillus  ***  Fish,  Etc. 
which  was  cultivated  from  an  inflammatory  tumor  in 
the  abdominal  wall  of  a  carp.  It  grows  well  at. low  tem- 
peratures, the  optimum  being  25°  C,  is  found  in  large 
numbers  in  the  lesions  within  giant  cells,  and  is  dis- 
tinctly pathogenic  for  frogs.  Certain  authors  state  that 
the  human  bacillus  when  inoculated  into  the  frog  under- 
goes changes  in  its  cultural  and  pathogenic  characteris- 
tics, eventually  resembling  the  organism  cultivated  from 
fish.  •■ 

Similar  bacilli  have  been  cultivated  from  a  form  of 
tuberculosis  in  the  turtle  (Friedman),  and  Blindsch- 
leiche — blind  worm   (Moeller). 

OTHER    ORGANISMS    RESEMBLING    THE    TUBERCLE    BACILLUS. 

Certain  other  organisms  of  low  pathogenicity  resemble 
the  tubercle  bacillus  in  their  acid-fast  properties,  their 
ability  to  grow  in  the  form  of  branching  threads,  and  to 
produce  tubercular  or  nodular  infections  of  a  local  na- 
ture in  animals.  They  may  be  placed  in  a  group  which 
includes  the  tubercle  bacillus. 

C.  Fraenkel,  also  Neufeld,  recognize  in  smegna  two  smegma  Bac- 
acid-fast  bacilli,  calling  one  "tuberculoid'^  because  of  its  illas  and  tlie 
morphologic  resemblance  to  the  tubercle  bacillus,  and  the  ?**^te^rten. 
other  "diphtheroid"  since  it  shows  the  pleomorphism  of 
the  diphtheria  bacillus.  One  of  these  organisms  may  be 
identical  with  the  "syphilis  bacillus"  of  Lustgarten. 
Smegma  bacilli  are  most  numerous  beneath  the  prepuce 
in  man  and  about  the  clitoris  and  vulva  in  women. 
Their  chief  significance  lies  in  the  danger  that  they  may 
be  mistaken  for  tubercle  bacilli  in  suspected  cases  of 
genitourinary  tuberculosis.  Smegma  bacilli  may  readily 
enter  the  urethra  in  women  and  be  carried  into  the  blad- 
der during  catheterization  or  cystoscopic  examination. 
In  man  the  danger  of  bacteriologic  error  may  be  elimi- 
nated largely  by  cleansing  the  glans  and  carefully  irrigat- 
ing the  urethra.  Urine  which  is  then  passed  is  not  likely 
to  contain  smegma  bacilli    (Young  and  Churchman). 


614  IXFECTION     AND     IMMUNITY. 

Bacilli  from  "Milk  bacilli"  and  "butter  bacilli"  are  acid-fast  or- 
^**^^  ^"**^*'  ganisms  resembling  the  tubercle  bacillus  morphologi- 
an  rass.  gg^jjy^  jj^  injecting  milk  into  guinea-pigs  as  a  test  for 
tuberculous  contamination,  Petri  occasionally  noted,  as 
a  consequence,  a  thick  membranous  growth  which  en- 
cased the  liver  and  spleen  and  bound  the  coils  of  intes- 
tines together.  The  omentum  was  thickened,  and  this 
structure  and  the  mesenteric  lymph  glands  contained 
nodules.  In  pure  culture  the  organism  is  pathogenic  for 
guinea-pigs  only  when  given  in  large  doses,  and  may  kill 
the  animals  in  several  weeks  with  the  anatomic  changes 
noted  above.  Its  virulence  is  increased  by  the  simul- 
taneous injection  of  butter.  It  is  not  pathogenic  for 
man   ( Herbert ) . 

Moeller  cultivated  organisms  resembling  the  tubercle 
bacillus  from  timothy  (timothy  bacillus),  from  manure, 
and  a  third  (grass  bacillus  II)  from  the  dust  of  a 
manger.  The  last  is  marked  with  great  pleomorphism, 
thread  formation  and  motility  in  young  cultures. 

The  leprosy  bacillus  and  the  B.  of  Lustgarten  which 
resemble  the  tubercle  bacillus  will  be  considered  later. 

PSEUDOTUBERCULOSIS    IN    ANIMALS. 

Although  some  of  the  organisms  described  above  are 
often  called  pseudotubercle  bacilli,  the  term  pseudo- 
tuberculosis is  now^  applied  somewhat  specifically  to  a 
nodular  disease  occurring  in  rats,  mice  and  sheep  (and 
perhaps  in  other  domesticated  animals),  and  in  which 
organisms  differing  from  the  tubercle  bacillus  in  stain- 
ing and  culture  properties,  morphology  and  pathogenic- 
ity, are  found.  The  clinical  course  and  anatomic 
changes  are  similar  in  the  three  animals  mentioned,  al- 
though the  organisms  are  different.  The  lymph  glands 
near  the  infection  atrium  become  enlarged  chiefly  by  a 
cellular  infiltrate  rather  than  extensive  proliferation  of 
fibrous  tissue.  The  nodules  undergo  a  soft  caseation 
very  early  and  rarely  show  calcification.  The  infection 
finds  its  way  to  other  sets  of  lymph  glands  and  may  be- 
come more  or  less  generalized  with  the  formation  of 
smaller  and  larger  sized  nodules. 
RatM  an«l  Pseudotuberculosis  of  rodents,  occurring  spontaneous- 
Mice,  ly  in  rats,  guinea-pigs,  rabbits  and  cats,  is  caused  by  an 
organism  of  considerable  pathogenicity,  and  may  occur 
in  epidemic  form  in  laboratory  animals.  Chickens  also 
may  contract  the  disease.  Intraperitoneal  inoculations 
in  guinea-pigs  are  fatal  in  a  few  days.  Spontaneous  in- 
fection takes  place  through  the  intestinal  tract,  and  re- 
gional organs  show  the  principal  changes.    The  liver  and 


LEPROSY.  615 

spleen  contain  many  nodules  which  may  be  as  large  as 
a  hazelnut,  and  which  are  frequently  caseated  in  the  cen- 
ter. The  organism  is  called  Bacillus  pseudotuberculosis 
rodentium  or  Streptohacillus  pseudotuherculosis  dor. 

The  disease  in  mice  is  caused  by  a  diphtheria-like  or-    siieep. 
ganism  called  Bacillus  pseudotuherculosis  murium  and 
is  pathogenic  especially  for  the  gray  mouse. 

A  similar  infection  in  sheep  is  of  more  importance  and 
occurs  with  some  frequency.  It  is  called  pseudotubercu- 
losis ovis,  and  the  bacillus  has  a  corresponding  name. 
The  organism  is  supposed  to  gain  entrance  through 
wounds  in  the  feet  and  legs,  following  which  the  adja- 
cent lymph  glands  become  involved,  and  the  infection 
may  be  transferred  to  the  lungs  and  other  organs 
through  the  lymphatic  circulation.  The  lesions  are 
nodular,  of  varying  size,  usually  surrounded  by  a  fibrous 
capsule,  and  are  either  semipurulent  or  undergo  early 
caseation.  They  may  be  found  in  all  the  visceral  or- 
gans. 

An  organism  resembling  that  cultivated  from  the 
sheep  has  occasionally  been  found  in  nodular  conditions 
in  cattle. 

II.    LEPROSY. 

Leprosy  existed  in  Eg}qDt  in  prehistoric  times  course  of 
and  extended  to  other  lands  onh^  when  inter-  ^  *"** 
course  was  established.  It  reached  Greece  at 
about  345  B.  Q.,  Italy  in  the  first  century 
before  Christ,  and  from  the  latter  country 
extended  to  Germany,  France  and  Spain.  Cru- 
saders returnins^  from  the  Orient  also  brousjht  back 
the  disease  in  later  times  and  eventually  all 
Europe  was  infected.  Leprosy  is  known  to  have 
existed  in  Great  Britain  in  the  tenth  century,  and 
from  that  country  it  was  carried  to  Iceland  and 
Greenland.  From  Germany  it  extended  to  the 
Scandinavian  countries,  and  from  the  latter  to 
Finland  and  Eussia.  It  also  reached  Eussia  from 
the  South  and  East,  and  in  the  South  it  was  at 
one  time  called  the  Crimean  disease.  The  West 
Indies  and  South  America  probably  were  infected 


Baclllns  of 
Leprosy. 


61G  INFECTION     AND     IMMUNITY. 

from  Spain,  and  through  these  channels  the  disease 
was  carried  to  the  southern  states.  The  leprosy  of 
the  western  states  seems  to  have  been  imported  by 
Norwegian  immigrants  chiefly.  In  1902  the 
United  States  leprosy  commission  found  278  case-s 
in  this  country.  One  hundred  and  eighty-six  of 
these  individuals  probably  contracted  the  disease 
in  this  country,  120  were  born  in  foreign  coun- 
tries and  145  were  native  born.  The  disease  also 
extended  around  the  globe  in  the  opposite  direc- 
tion, reaching  China,  Japan  and  the  East  Indian 
islands  from  India.  The  Sandwich  Islands  be- 
came infected  in  the  nineteenth  century. 

The  contagiousness  of  the  disease  appears  to 
have  been  recognized  at  a  very  early  period.  In 
636  A.  D.  leprosy  houses  were  instituted  in  Italy 
and  other  countries,  and  the  practice  of  segregat- 
ing lepers  soon  became  general.  The  hospitals 
were  called  Lazarus  houses  in  middle  Europe  and 
St.  George  houses  in  Scandinavian  countries. 
Pipin  and  Charles  the  Great  declared  marriage  be- 
tween lepers  illegal.  The  rapid  disappearance  of 
leprosy  in  middle  Europe  during  the  sixteenth 
century  is  ascribed  largely  to  the  segregation  of 
the  patients. 

In  1872  Hansen  announced  that  small  rods, 
sometimes  intracellular  and  sometimes  free,  were 
to  be  found  constantly  in  teased  preparations  of 
leprous  tissue.  These  rods,  leprosy  bacilli,  are 
now  universally  recognized  as  the  cause  of  the 
disease,  and  in  1879  they  were  stained  by  Neisser 
and  a  year  later  by  Hansen.  The  organism  is  non- 
motile,  has  about  the  dimensions  of  the  tubercle 
bacillus,  the    same    staining   reactions,    and    fre- 


LEPROSY     BACILLUS.  617 

qiiently  shows  a  beaded  appearance  (degeneration 
forms  ?  ).  It  is  said  to  take  up  dyes  more  readily 
than  the  tubercle  bacillus,  but  the  difference  is  not 
so  great  as  to  be  distinctive.  It  stains  by  Gram's 
method. 

Duval  has  recently  succeeded  in  cultivating  the 
leprosy  bacillus  on  media  prepared  as  follows : 

The  rind  was  carefully  removed  from  the  fruit  portion  cultivation 
of  fully  matured  green  bananas,  every  precaution  to 
avoid  contamination  being  used,  and  large  blocks  of  the 
fruit,  after  slanting  one  surface  with  a  sharp  knife,  were 
introduced  into  suitable  sterile  glass  cylinders  provided 
at  the  bottom  with  cotton  plugs  saturated  in  sterile  dis- 
tilled water.  These  plugs  served  not  only  as  support  for 
the  banana,  but  as  a  source  of  constant  supply  of  mois- 
ture. Sterile  1  per  cent,  solutions  of  tryptophan,  cystein 
(made  from  protein),  and  leucin  Avere  next  prepared  and 
a  portion  of  each  poured  on  and  allowed  to  saturate  the 
banana.  These  solutions  were  used  separately  and  in 
varying  combinations,  in  order  to  determine  on  which 
the  B.  leprcc  would  grow  best  or  grow  at  all.  Both  the 
banana  and  agar,  which  was  saturated  in  a  1  per  cent, 
•solution  of  cystein,  proA^ed  an  excellent  medium  for  the 
artificial  cultivation  of  the  leprosy  bacilli  when  incu- 
bated at  from  32  to  35  degrees  C.  The  maximum  groAvth 
occurred  at  a  temperature  of  32  degrees  C.  Light  seems 
to  favor  the  growth  of  B.  leprce;  cultures  kept  in  a  glass 
incubator  regulated  at  32  degrees  C.  greAV  more  rapidly 
than  those  in  the  dark  chamber  uoider  similar  conditions. 
Multiplication  began  early  in  the  transplants  and  Aisible 
growth  developed  in  the  form  of  small,  glistening,  white 
colonies  in  from  four  to  six  weeks.  Growth  also  occurred 
on  the  banana  and  agar  when  a  solution  of  cystein  and 
tryptophan  had  been  added.  The  fact  that  growth 
occurred  on  the  protein-cystein  medium,  and  not  on  the 
others  except  in  the  presence  of  it,  shows  very  conclu- 
sively that  B.  lepnc  utilizes  the  end-products  of  digestion 
and  not  the  products  of  cell  metabolism.  At  least  it  is 
reasonable  to  assume  that  this  is  the  case,  if  deductions 
may  be  drawn  from  these  experiments.     Multiplication 


618  INFECTION     AND     IMMUNITY,. 

in  vitro  of  an  acid-fast  organism  was  obtained  from  the 
transplanted  leprosy  tissue  on  the  above  mentioned  media 
from  four  cases  of  leprosy  which  corresponded  in  every 
essential  to  the  leprosy  bacillus.  i>rot  only  did  the 
leprosy  bacilli  develop  in  the  original  cultures  but  they 
continued  to  grow  in  subcultures.  That  the  artificial 
groAvth  is  B.  leprw  there  can  be  no  doubt,  as  the  morpho- 
logic and  cultural  features  and  the  animal  tests  have 
clearly   proved. 

Lugai  lias  shown  that  the  leprosy  bacillus  is 
pathogenic  for  Japanese  dancing  mice.  The  ba- 
cilli not  only  multiply  at  the  site  of  inoculation 
but  become  disseminated  throughout  the  body, 
producing  lesions  having  the  typical  characters  of 
leprous  lesions  in  man.  Nicolli  is  said  to  have 
produced  leprous  nodules  in  monkeys  by  inocu- 
lating them  with  diseased  tissue,  and  finally  Duval 
has  produced  typical  leprosy  of  the  tubercular  type 
in  the  monkey  (Macaciis  rhesus)^  by  means  of  pure 
cultures  of  leprosy  bacillus. 

So  far  as  known,  the  oi'ganism  has  no  natural 
existence  outside  the  human  body,  and  it  is  dis- 
seminated only  by  the  secretions  of  the  diseased. 
It  is  discharged  chiefly  through  the  secretions  of 
the  nose  and  the  upper  respiratory  passages,  the 
surfaces  of  which  are  so  commonly  the  seat  of  lep- 
rous ulcers,  and  also  through  ulcerating  lesions  of 
the  skin.  Expectoration,  sneezing  and  coughing 
have  approximately  the  same  significance  for  the 
dissemination  of  leprosy  bacilli  as  of  tubercle  ba- 
cilli. However,  the  organisms  which  are  found  in 
the  sputum  and  nasal  secretions  appear  to  be 
largely  degenerated,  a  condition  which  may  lessen 
TrannmisHion.  the  infcctiousncss  of  thcsc  substauccs. 

The  infectiousness  of  the  leprosy  bacillus  is  of  a 
low  character.     "Epidemiologic  experience  teaches 


Atria. 


TRANSMISSION  619 

that  infection  occurs  only  through  intimate  and 
prolonged  association  with  the  diseased,  in  which 
doubtless  uncleanliness  plays  a  very  important 
role"  (Gotschlich).  A  leprous  husband  eventually 
infects  his  wife,  and  the  children  of  lepers  com- 
monly develop  the  disease  early  in  life.  The  high 
percentage  of  leprosy  which  is  noted  among  the 
laundresses  of  infected  localities  indicates  that  the 
disease  may  also  be  transmitted  by  indirect  contact. 
Gotschlich  throws  some  doubt  on  the  importance 
of  dust  infection  since  so  many  of  the  bacilli  found 
in  sputum  appear  to  be  degenerated.  Nothing  is 
known  of  the  resistance  and  viability  of  the  organ- 
ism outside  the  body. 

On  account  of  the  early  appearance  and  almost  infection 
constant  occurrence  of  leprous  lesions  in  the  nasal 
passages  Strieker  believes  that  the  latter  constitute 
the  chief  infection  atrium;  of  this  Hansen  is  not 
positive.  Nasal  ulcers  may  be  present  in  latent 
or  apparently  healed  cases.  Kolle  cites  a  case  show- 
ing extensive  involvement  of  the  spleen  and  liver 
in  which  the  intestinal  tract  was  considered  tlie  in- 
fection atrium.  In  som.e  instances  in  which  the 
disease  is  first  noted  in  the  feet,  the  organisms 
are  supposed  to  gain  entrance  with  infected  soil 
through  abrasions  in  the  skin.  According  to  Cor- 
nii  and  Babes,  infection  may  take  place  through 
the  hair  follicles  and  sebaceous  glands.  The  theory 
of  Jonathan  Hutchinson  that  leprosy  may  be  con- 
tracted through  eating  diseased  fish,  or  that  the  lat- 
ter in  some  way  may  render  individuals  susceptible 
to  infection  is  not  now  credited.  Hereditary 
acquisition  of  the  disease  is  of  doubtful  occur- 
rence, although  the  bacilli  have  been  found  in  ova 
(Babes)    and  commonly  are  present  in  enormous 


fi20  INFECTION     AND     IMMUNITY. 

numbers  in  the  testicles.  Hansen  states,  however, 
that  he  has  never  found  them  in  the  female  gen- 
erative organfe. 
liocatiou  The  presence  of  large  masses  of  bacilli  in  leprous 
tissues  is  a  characteristic  of  the  disease.  To  a  large 
extent  they  are  intracellular  and  they  are  often 
grouped  in  such  a  way  as  to  resemble  bundles  of 
cigars.  Hansen  believes  that  the  bacillus  is  essen- 
tially an  intracellular  parasite,  and  that  it  becomes 
extracellular  only  as  a  result  of  degeneration  and 
disintegration  of  infected  cells.  Unna,  on  the 
other  hand,  considers  their  location  in  lymph 
spaces  as  most  characteristic.  They  appear  to  be 
carried  to  distant  parts  through  the  lymphatics. 
Certain  large  vacuolated  cells,  the  lepra  cells  of 
Virchow,  the  gloti  of  Hansen,  which  are  filled  to 
bursting  with  the  leprosy  bacilli,  are  characteristic 
of  the  disease.  Unna  and  others  consider  these 
bodies  as  zooglear  masses  rather  than  as  intracel- 
lular accumulations,  and  Kanthack  interprets  them 
as  bacillary  thrombi  in  the  lymphatic  vessels.  The 
nodules,  or  lepromas,  consist  of  granulation  tissue, 
containing  many  round  and  epithelioid  cells,  lepra 
cells  and  occasional  multinuclear  giant  cells.  In 
cutaneous  macules  columns  of  round  cells  surround 
the  blood  vessels,  there  is  some  proliferation  of 
epithelioid  cells,  but  relatively  few  bacilli.  The 
bacilli  are  most  numerous  in  the  nodular  lesions. 
They  are  found  in  the  Glissonian  tissue  of  the  liver, 
in  the  pulp  and  follicles  of  the  spleen,  in  the  glom- 
eruli and  interstitial  tissue  of  the  kidne3^s  when 
these  organs  are  involved,  in  the  nerves  in  both 
the  nodular  and  maculoanesthetic  forms  of  the 
disease,  and  in  the  vascular  endothelium.  They 
have  been  demonstrated  often  in  the  ganglionic 


LEPROSY     BACILLUS.  621 

cells  of  the  posterior  root  ganglia.  Their  occur- 
rence in  these  cells  leads  Metchnikoff  to  say  that 
the  latter  have  phagocytic  properties 

In  view  of  the  chronic  course  of  leprosy  and  the  E"*^***®^*'^  (')• 
absence  of  signs  of  intoxication  over  considerable 
periods^  it  seems  probable  that  the  bacillus  secretes 
little  or  no  soluble  toxin.  From  time  to  time^  how- 
ever, patients  with  tubercular  leprosy  develop  fever, 
which  may  persist  for  weeks  or  months  and  event- 
ually terminate  in  death.  During  such  attacks 
the  nodules  not  infrequently  enlarge,  become  soft 
and  later  disappear.  Lie  conceives  that  such 
periods  represent  massive  infection  of  the  blood 
with  the  bacilli,  and  that  at  this  time  the  latter 
undergo  extensive  disintegration  and  liberate  en- 
docellular  toxins  to  which  the  toxic  phenomena  are 
due.  It  is  a  remarkable  fact  that  intercurrent  in- 
fections, as  measles  and  smallpox,  and  the  adminis- 
tration of  potassium  iodid,  cause  a  similar  enlarge- 
ment, softening  and  final  disappearance  of  leprous 
nodules,  accompanied  by  marked  degenerative 
changes  in  the  bacilli.  Hansen  is  of  the  opinion 
that  the  fever  induced  by  these  conditions  has  an 
actual  curative  effect,  although  its  influence  is  not 
readily  analyzed.  He  quotes  the  opinion  of  Dan- 
ielssen  that  potassium  iodid  may  be  used  to  deter- 
mine the  cure  of  leprosy,  which  would  be  indicated 
by  absence  of  a  febrile  reaction. 

General  confidence  is  not  felt  in  the  "leprolin" 
which  Rost  prepared  from  his  cultures  of  the  lep- 
rosy bacillus  (?).  His  cultures  are  said  to  have 
been  mixtures  of  micro-organisms. 

Because  of  the  failure  until  recently  to  cultivate  Miuy^and 
the  leprosy  bacillus,  experimental  work  with  the  Defense* 


622  INFECTION     AND     IMMUNITY, 

serum  and  cells  of  man  and  animals,  by  which 
conclusions  as  to  the  defensive  powers  of  the  body 
might  be  drawn,  can  not  be  carried  out.  It  seems 
probable  that  all  men  are  susceptible  to  leprosy 
under  the  proper  conditions.  Sauton  states  that 
children  of  from  4  to  5  years  are  particularly 
liable  to  infection.  Other  conditions  which  may 
increase  suspectibility  are  of  a  conjectural  nature. 
It  is  possible  that  leprosy  predisposes  to  tuber- 
culous infection. 

The  condition  in  leprosy  seems  to  be  that  of  an 
organism  of  low  virulence  against  which  the  body 
possesses  no  decisive  protective  agency.  The  reac- 
tions for  the  most  part  are  of  a  local  nature,  involv- 
ing the  proliferation  of  connective  tissue  and  blood 
vessels,  and  the  accumulation  of  lymphocytes.  That 
phagocytosis  by  macrophages  (lymphocytes,  con- 
nective tissue,  endothelial  and  ganglionic  cells)  is 
a  factor  which  antagonizes  the  proliferation  of  the 
bacilli  is  suggested  by  the  large  number  of  bacilli 
which  are  found  in  these  cells. 
Propiiyiaxis.  The  principles  of  prophylaxis  may  be  illustrated 
by  citing  the  practices  in  Norway.  Originally  all 
lepers  were  confined  to  institutions.  At  the  pres- 
ent, however,  only  indigent  lepers  and  those  who 
can  not  be  suitably  cared  for  at  home  are  required 
to  enter  an  asylum,  where  they  live  under  the  best 
hygienic  conditions.  Other  patients  are  allowed  to 
remain  at  home,  with  the  understanding  that  they 
sleep  alone  and,  if  possible,  have  separate  rooms, 
that  their  clothing,  linen  and  eating  utensils  be 
used  by  no  one  else,  and  that  proper  precautions 
be  taken  in  the  washing  of  linen.  Dressings  and 
bandages  must  be  burned.    Under  these  regulations 


of  the 
Disease. 


GLANDERS.  623 

the  number  of  lepers  in  Norway  has  decreased  from 
2,870  in  1856  to  577  in  1900.  Banishment  to  the 
Island  of  Molokai  is  practiced  in  the  Sandwich  Is- 
lands. Segregation  of  lepers  should  be  brought 
about  in  this  country. 

Carasquilla  attempted  the  production  of  an  anti- 
leprosy  serum  by  immunizing  horses  with  the  blood 
of  leprous  patients.  Although  a  few  favorable  re- 
ports concerning  its  effects  appeared  it  has  not 
proved  of  value  in  the  hands  of  others. 

III.    GLANDERS   (FARCY). 

Under  natural  conditions  the  horse  is  the  chief  occtirrence 
sufferer  from  glanders  or  farcy,  the  former  name 
being  applied  to  the  disease  as  it  occurs  in  the  nose, 
the  latter  when  in  the  skin.  These  names  are  relics 
of  the  time  when  the  two  forms  of  the  disease  were' 
not  recognized  as  having  a  common  etiology.  In 
either  locality  the  disease  may  be  acute  or  chronic, 
and  in  the  horse  about  90  per  cent,  of  the  cases 
are  chronic.  The  ass  is  occasionally  infected,  and 
in  this  animal,  as  well  as  in  man,  an  acute  general 
infection  (bacillemia)  frequently  develops,  in  ad- 
dition to  the  cutaneous  and  nasal  lesions  which 
characterize  the  disease.  Fortunately,  glanders  in 
man  is  rare.  Cows  and  rats  are  immune,  or  nearly 
so ;  the  sheep,  goat  and  dog  have  fairly  high  resis- 
tance, although  they  may  be  infected  artificially; 
the  dog  and  rabbit  are  moderately  susceptible,  and 
for  the  guinea-pig  and  members  of  the  cat  family 
(tiger,  lion  and  leopard),  the  bacillus  is  very  vir- 
ulent. Infection  of  the  last-named  animals  has 
been  noted  in  menageries  as  the  result  of  feeding 
them  with  the  meat  of  a  horse  which  had  died  of 
glanders.    The  acute  infection  usually  is  fatal,  and 


624  nFECTION     AXD     IMMUNITY. 

complete  recovery  from  the  chronic  form  of  the  dis- 
ease is  infrequent.  Something  less  than  50  per 
cent,  of  the  chronic  infections  in  man  terminate 
in  recovery. 
Bacillus  The  specific  microbe,  Bacillus  mallei,  discovered 
in  1882  by  Loeffler  and  Schiitz,  is  an  aerobic  or- 
ganism which  has  approximately  the  morphology 
and  size  of  the  tubercle  bacillus,  but  lacks  the  acid- 
fast  property  of  the  latter.  It  stains  with  anilin 
dyes,  especially  carbol  fuchsin,  but  not  by  Gram's 
method.  With  weak  staining  it  shows  a  granular 
structure.  It  grows  well  on  ordinary  culture  media, 
showing  a  characteristic  appearance  on  potato.  In 
unfavorable  media  it  may  produce  threads,  while 
under  more  favorable  conditions  coccus-like  forms 
are  seen.  Marked  involution  forms  occur  on  media 
containing  3  per  cent,  of  sodium  chlorid 
(Wherry).  The  optimum  temperature  for  growth 
is  from  30°  to  40°  C. 
Resistance       The  bacillus  is  oulv  moderatelv  susceptible  to 

and  E^ndo-  .... 

sunlight,  by  which  it  is  killed  in  about  twenty-four 
hours.  It  withstands  freezing,  lives  for  two  or 
three  weeks  in  a  dried  condition  at  room  tempera- 
ture, and  is  killed  by  a  temperature  of  from  56°  to 
60°  C.  in  from  ten  minutes  to  one  and  one-half 
hours,  depending  on  the  amount  and  character  of 
the  medium  in  which  it  lies.  Its  resistance  to  the 
ordinary  disinfectants  (corrosive  sublimate,  car- 
bolic acid,  etc.),  is  not  high.  Milk  of  lime  and 
solutions  of  calcium  chlorid  are  suitable  for  the  dis- 
infection of  stalls.  In  culture  media  the  organism 
secretes  no  soluble  toxin,  but  it  contains  an  endo- 
toxin which  probably  is  one  of  the  constituents  in 
the  various  preparations  of  mallein. 


toxin. 


MALLEIN. 


625 


The  method  by  which  the  mallein  of  Koux  and 
Nocard  is  prepared  is  idontical  with  that  used  in 
the  preparation  of  the  old  tuberculin.  A  virulent 
strain  of  the  glanders  bacillus  is  allowed  to  grow 
for  some  time  (from  two  weeks  to  two  or  three 
months)  in  bouillon  which  contains  from  4  to  5 
per  cent,  of  glycerin^  the  culture  is  then  sterilized 
by  heat  and  the  bacteria  removed  by  filtration. 
The  toxin  is  not  destroyed  by  high  temperature. 
Other  preparations,  also  called  mallein,  are  made 
by  extracting  ground-up  bacilli  with  a  solution  of 
glycerin  and  water  (Helman,  Kalning),  or  with 
water  alone  (Kalning  and  others)  ;  by  killing  a 
liquid  culture  of  the  bacillus  (Bromberg)  ;  or  by 
precipitating  bouillon  filtrates  with  absolute  alco- 
hol (de  Schweinitz  and  Kilbourne),  or  with  am- 
monium sulphate  or  magnesium  sulphate.  The 
dry  powders  "morvin^^  and  "dried  mallein'^  are 
prepared  by  one  or  another  of  these  precipitation 
methods. 

Glanders  bacilli  are  found  only  in  the  tissues 
and  secretions  of  diseased  animals,  and  the  nasal 
discharges  of  the  latter  are  the  chief  means  of  con- 
taminating feed,  water  and  stables  through  which 
the  disease  usually  is  carried  to  other  animals. 
The  glanders  bacillus  does  not  readily  penetrate 
the  intact  skin  and  mucous  membranes,  although 
occasionally  it  may  gain  entrance  through  the  hair 
follicles  or  sweat  ducts.  In  the  presence  of  even 
slight  defects  in  these  surfaces,  as  those  caused  in 
the  mouth  or  nostrils  of  horses  by  hay  or  other 
food,  infection  readily  occurs.  According  to  No- 
card,  invasion  takes  place  commonly  through  the 
gastrointestinal  tract  following  the  ingestion  of  in- 
fected feed  or  water.    Although  involvement  of  the 


Preparation 
of  Mallein. 


Distribution 
of  Bacilli  and 
Infection 
Atria. 


626  INFECTION     AND     IMMUNITY. 

intestines  and  adjacent  tissues  frequently  results, 
the  organisms  may  become  generalized,  causing  the 
disease  in  the  nose,  skin  or  other  organs,  without 
the  establishment  of  foci  in  the  intestines. 

In  man  infection  occurs  chiefly  through  abra- 
sions in  the  skin,  and  perhaps  also  through  the 
nose,  to  which  the  bacilli  have  been  carried  by 
soiled  fingers  or  other  means.  In  experimental 
work  with  glanders  extreme  care  is  necessary  as 
infection  occurs  very  easily.  Glanders  has  been 
transmitted  to  animals  by  rubbing  bacilli  on  the 
intact  skin.  Several  cases  of  acute  glanders,  end- 
ing fatally,  have  occurred  in  laboratory  workers  as 
the  result  of  accidental  inoculation.  There  appears 
to  be  little  danger  to  man  in  eating  the  meat  of 
horses  in  which  the  disease  was  localized,  pro- 
vided the  meat  has  been  well  cooked.  Such  meat 
was  fed  to  soldiers  in  one  instance  with  no  ill 
results. 
Rea^'io'ns^  Variations  in  the  course  of  the  disease  and  in  the 
intensity  of  the  pathologic  changes  in  different 
cases  probably  depend  on  variations  in  the  resist- 
ance of  the  host  and  in  the  virulence  of  the  para- 
site. In  acute  general  infections  in  man,  follow- 
ing an  incubation  period  of  from  two  to  five  days, 
during  which  the  point  of  inoculation  becomes  vio- 
lently inflamed,  a  severe  febrile  condition  develops, 
which  is  accompanied  by  general  pains,  swollen 
joints,  a  macular  eruption,  and  often  muscular  and 
subcutaneous  abscesses.  In  a  short  time  nodules 
and  indurated  cords,  made  up  of  a  leucocytic  exu- 
date, edematous  fluid  and  proliferating  connective 
tissue  cells,  form  in  the  subcutaneous  lymphatic 
channels,  and  mark  the  progress  of  the  infection 


PROTECTIVE   PROCESSES   IN    GLANDERS.  627 

toward  the  lymph  glands.  The  nodules,  and  also 
the  cordSj  commonly  undergo  softening,  and  ab- 
scesses form  and  rupture  through  the  skin.  Nod- 
ules similar  to  those  in  the  skin  develop  in  various 
organs  of  the  body;  in  the  nose  they  break  down 
and  constitute  ulcers.  In  chronic  infections  the 
lesions  are  of  the  same  nature,  although  they  evolve 
more  slowly  and  tend  to  remain  limited  to  particu- 
lar regions.  Nasal,  pharyngeal,  tracheal  or  pulmon- 
ary glanders  are  forms  of  the  disease  which  are  en- 
countered in  the  horse.  Connective  tissue  develop- 
ment is  more  marked  in  chronic  than  in  acute 
glanders,  although  the  peculiar  liquefaction,  sup- 
puration and  ulceration  of  the  lesions  occur  in  the 
former  as  well  as  in  the  latter.  Moderate  leucocy- 
tosis  is  found  in  the  blood  (12000-14000). 

The  nature  of  the  patholos^ic  chans^es  found  in   Protective 

1  .  T      1  .  Processes. 

glanders,  the  frequent  chronic  and  the  progressive 
course  of  the  disease,  and  the  fact  that  infection 
does  not  confer  distinct  immunity,  are  conditions 
which  ally  glanders  closely  to  tuberculosis, 
pseudo-tuberculosis  and  leprosy.  The  essential 
lesion  is  the  "infectious  granuloma,'''  and  it  is  prob- 
able that  the  new  connective  tissue  which  is  formed 
is  to  no  small  extent  a  factor  in  limiting  the  exten- 
sion of  the  infection.  Nodules  of  glanders  fre- 
quently are  isolated  by  the  surrounding  reaction, 
the  centers  caseate  and  the  contents  eventually  are 
discharged  through  the  skin;  cicatrization  and 
healing  in  many  lesions  follow  evacuation.  Phago- 
cytosis of  the  bacilli  by  the  epithelioid  cells  and  leu- 
cocytes in  the  nodules  is  said  to  be  rather  extensive. 
Agglutination  of  glanders  bacilli  takes  place  in 
high  dilution  with  the  serum  of  horses  affected 
with  glanders.     An  agglutination  with  serum  in 


628  INFECTION     AND     IMMUNITY. 

•  1  to  500  dilution  is  a  valuable  aid  to  diagnosis. 
N^ornial  horse  serum  is  said  to  agglutinate  glan- 
ders bacilli  at  times  in  1  to  250  dilution.  Agglu- 
tination in  dilution  of  1  to  5,000  and  1  to  10,000 
has  been  observed.  By  active  immunization  of 
animals  an  agglutinating  serum  may  be  obtained, 
and  such  a  serum  mav  be  used  for  the  diai>nosis 
of  glanders  bacilli.  Precipitins  are  also  formed. 
Serum       Treatment  of  slanders  with  immune  serums  has 

Therapy  a,n<l  °  oi       i 

Use  of  not  been  successful.  Such  treatment  has  been  at- 
tempted with  serum  prepared  by  immunization 
with  mallein  (Semmer),  and  with  the  serum  of 
diseased  animals  (Hell  and  Toeper).  The  value 
of  mallein  in  the  diagnosis  of  glanders  or  farcy  is 
similar  to  that  of  tuberculin  in  tuberculosis.  Al- 
though it  causes  a  rise  in  the  temperature  of  nor- 
mal animals  when  given  in  considerable  doses,  the 
reaction  produced  in  infected  animals  is  so  much 
more  intense,  and  occurs  with  such  smaller  doses, 
that  it  is  generally  considered  as  specific  in  nature. 
Some  doubt,  however,  has  been  thrown  on  the  spe- 
cificity of  the  reaction  from  the  facts  reported  by 
various  observers  that  toxic  substances  from  other 
organisms,  as  tuberculin  and  preparations  from 
the  pneumobacillus  of  Friedlander,  Bacillus 
pyocyaneus,  etc.,  cause  similar  phenomena  in  ani- 
mals suffering  from  glanders.  Wladimiroff  asserts, 
however,  that  the  reactions  caused  by  these  sub- 
stances differ  from  that  of  maliein. 

For  diagnosis  a  dose  must  be  used  which  causes 
no  reaction  in  a  normal  animal,  and  this  varies 
with  different  preparations.  The  typical  reaction 
has  two  essential  components:  1,  A  rise  in  tem- 
perature which  begins  in  from  six  to  twelve  hours 


ACTINOMYCOSIS.  629 

after  the  injection,  reaches  its  maximum  (from  40° 
to  43°  C.)  in  from  six  to  eight  hours  later,  where 
it  remains  for  a  few  hours,  then  gradually  sinks, 
only  to  recur  on  the  second  day ;  2,  an  edematous 
and  inflammatory  tumor  at  the  point  of  injection, 
which  begins  in  from  six  to  eight  hours,  and  runs 
its  course  in  from  three  to  eight  days,  ending  in 
resorption  (Wladimiroif).  Veterinarians  gener- 
ally agree  that  mallein  is  a  valuable  diagnostic 
agent.  Mallein  also  has  been  used  in  the  treatment 
of  glanders,  but  with  rather  doubtful  results. 

Bacteriologic  diagnosis  is  accomplished  by  culti- 
vating the  bacilli  from  the  abscess  or  secretions  and 
testing  the  virulence  of  the  culture  by  animal  ex- 
periments (guinea-pig). 

IV.    RHIN-QSCLEROMA. 

(See  page  572.) 

V.   ACTINOMYCOSIS. 

Actinomycosis  is  a  chronic  infectious  disease  of 
man  and  animals,  the  lesions  of  which  present, 
characteristically,  a  central  mass  of  purulent  and 
necrotic  material  containing  colonies  of  "ray 
fungi,"  about  or  through  which  is  disposed  an 
abundant  growth  of  granulation  or  fibrous  tissue. 
In  young  or  rapidly  progressing  lesions  the  amount 
of  purulent  material  is  large,  while  in  older  lesions 
well  formed  connective  tissue  is  more  conspicuous. 
The  disease  prevails  especially  among  cattle,  al- 
though it  is  met  occasionally  in  the  horse,  hog, 
sheep,  dog,  cat  and  other  animals ;  man  is  infected 
not  infrequently. 

Although  fungous  threads  had  been  found  in 
diseases    resembling   actinomycosis    in    1845    and 


Resistance. 


630  IXFECTIO^'     AND     IMMUXITY. 

later,  Bollinger,  in  1877,  gave  the  first  accurate  de- 
scription of  the  disease  in  cattle,  and  in  1878  J. 
Israel  described  it  as  a  new  disease  in  man.  A 
short  time  later  Ponfick  demonstrated  the  identity 
of  bovine  and  human  actinomj^cosis. 

The  specific  organism,  Actinomyces  bovis  et 
liominis,  on  culture  media  consists  of  a  mass  of  del- 
icate threads  which  exhibit  "true  branching^''  and 
which,  to  a  certain  extent,  segment  to  form 
"spores.'^  The  radially  arranged  groups  of  cells 
which  occur  as  somewhat  characteristic  sulphur- 
yellow  macroscopic  granules  in  the  pus  of  the  actin- 
omycotic abscesses,  and  which  give  to  the  organ- 
ism the  name  of  "ray  fungus,"  are  essentially  a 
manifestation  of  parasitic  existence,  although  col- 
onies developing  on  media  which  contain  serum 
or  ascitic  fluid  may  show  a  degree  of  "club"  for- 
mation (Wright).  Each  granule  represents  a  col- 
ony of  organisms  the  members  of  which  possess 
club-shaped  extremities,  and  in  the  center  of  the 
mass  and  extending  from  it  are  many  of  the  deli- 
cate threads  found  in  cultures  of  the  organism.  It 
grows  on  various  culture. media,  often  as  a  mold, 
and  stains  by  Gram's  method. 

The  actinomyces  is  an  organism  of  considerable 
resistance.  Cultures  remain  alive  for  one  year  or 
more  when  in  a  dried  condition  and  the  spores  in 
one  instance  germinated  after  having  been  pre- 
served for  six  years.  A  temperature  of  80°  C. 
for  fifteen  minutes  kills  the  spores  (Berard  and 
Kicolas).  AYhen  suspended  in  bouillon,  spores  are 
killed  in  fifteen  hours  by  direct  sunlight,  but  when 
thoroughly  dried,  approximately  ten  days'  expos- 
ure produced  no  injury. 


ACTINOMYCOSIS. 


631 


Attempts  to  place  the  actinomyces  in  a  botanic 
system  have  resulted  in  many  differences  of  opin- 
ion. By  some  investigators  they  are  considered  as 
an  independent  family  midway  between  the  hy- 
phomycetes  and  the  schizomycetes  (bacteria),  oth- 
ers place  them  under  the  hyphomycetes  in  the  group 
of  the  strep tothrix,  while  still  others  consider  them 
as  pleomorphous  bacteria,  placing  them  in  the 
group  cladothrix.  Petruschky  recognizes  acti- 
nomyces, streptothrix,  cladothrix  and  leptothrix  as 
genera  in  the  family  trichomyces,  the  latter  belong- 
ing to  the  order  hyphomyces.  Biological  variations 
which  have  been  encountered  have  led  to  the  rec- 
ognition of  several  species  of  actinomyces,  among 
which  are  a  number  of  non-pathogenic  forms. 
Wright  limits  the  term  actinomyces  to  those  strains 
which  produce  colonies  of  club-shaped  organisms 
in  animal  tissues. 

Many    attempts   have   been   made   to   transmit   Artificial 

.  .         ,      1        .  1    1-  n  -11      Infection. 

actinomycosis  to  anmials  by  inoculating  them  with 
the  diseased  tissues  of  animals  and  man,  and  with 
pure  cultures  obtained  from  these  tissues.  Al- 
though a  number  of  experimenters  have  reported 
positive  results,  the  attempts  usually  have  been 
fruitless.  Probably  Wright  has  been  more  success- 
ful than  others  in  producing  actinomycotic  lesions 
in  rabbits  and  guinea-pigs  by  the  inoculation  of 
pure  cultures.  Colonies  of  club-shaped  organisms 
developed  with  considerable  uniformity.  In  many 
instances  the  infection  remains  localized,  not  caus- 
ing the  progressive  and  destructive  changes  which 
actinomycosis  produces  when  it  occurs  naturally. 

The  or2:anism  has  been  found  on  trains,  straws  Transmission 

1  1  •     T         n    !>      1         ■  1         1  •   1     •  1  •  and  Infection 

and  other  kinds  of  feed,  with  which  it  may  be  im-  Atria. 
planted  in  the   soft  parts  of  the  mouth    (gums, 


632  INFECTION     AND     IMMUNITY. 

tongue),  or  in  carious  teeth.  Transmission  to  man 
by  eating  the  meat  of  actinomycotic  cattle  has  not 
been  noted.  In  man  the  disease  is  primary  in  the 
internal  organs  (lungs,  intestines,  liver,  brain, 
etc.)  in  a  large  percentage  of  the  cases,  whereas 
"lumpy  jaw''  is  rare.  The  disease  extends  locally 
Ly  the  gradual  involvement  of  adjacent  tissues, 
which  in  time  become  occupied  by  sinuses,  ab- 
scesses and  masses  of  connective  tissue.  Numerous 
"spores"  aiul  bacillus-like  cells,  having  their  source 
in  the  fungous  threads,  abound  in  the  vicinity  of  a 
colony.  The  occurrence  of  such  forms  in  leuco- 
cytes and  other  large  mononuclear  cells  has  led 
some  to  the  view  that  the  micro-organisms  may 
be  carried  to  neighboring  tissues  or  to  distant 
parts  as  cell  inclusions.  In  cattle  the  disease  usu- 
ally is  more  chronic  than  in  man,  more  fibrous  tis- 
sue is  formed  and  metastases  in  internal  organs 
are  less  frequent.  In  man  the  lesions  are  more 
purulent  in  character,  large  abscesses  sometimes 
form  as  in  the  liver,  and  metastases  in  visceral  or- 
gans are  more  common.  Cases  of  general  acti- 
nomycosis are  occasionally  met  with  in  both  catt- : 
and  man. 
Propiiyiaxis.  Little  cau  bc  said  in  the  way  of  prophylaxis 
against  actinomycosis.  Knowing  the  part  that  in- 
fected grains,  straws,  etc.,  play  in  causing  infec- 
tion, the  practice  of  biting  or  chewing  grains  or 
of  using  straws  as  toothpicks,  evidently  is  one 
which  affords  opportunity  for  infection.  The  pres- 
ence of  carious  teeth  has  often  been  suggested  as 
a  predisposing  condition  for  infection. 
immanity  Practically  nothing  is  known  concerning  the  de- 
tibiiity'  gree  to  which  susceptibility  to  actinomycosis  pre- 
vails, and  the  question  of   immunity  to  the  disease 


MADURA     FOOT.  633 

remains  "anexplorecL  The  inability  to  reproduce 
the  infection  in  animals  at  will  renders  a  satisfac- 
tory study  of  these  questions  very  difficult.  The 
presence  of  large  numbers  of  polymorphonuclear 
leucocytes  in  the  vicinity  of  the  organisms  sug- 
gests, but  does  not  prove,  that  they  may  have  some 
influence  in  combating  the  infection.  Surely  the 
abundant  mass  of  connective  tissue  which  develops 
about  the  abscesses  and  sinuses  aids  in  confining 
the  process  to  a  definite  region. 

That  the  iodid  of  potassium  has  a  curative  influ- 
ence on  some  cases  of  actinomvcosis  seems  to  have 
been  well  demonstrated.  The  principles  by  which 
it  produces  its  effects  are  unknown. 

VI.    MADURA   FOOT. 

Mycetoma^  or  Madura  foot,  resembles  actinomy-  Mycetoma. 
cosis  in  the  formation  of  abscesses,  sinuses  and 
granulation  tissue,  but  it  shows  a  peculiar  predilec- 
tion for  the  foot,  which  probably  is  explained  by 
the  greater  exposure  of  this  part  to  infection.  This 
disease  differs  from  actinomycosis  in  that  the 
course  is  more  chronic  and  it  is  never  accompanied 
by  generalized  infection.  The  bones  are  not  in- 
volved so  frequently  as  in  actinomycosis.  Granules 
similar  to  those  of  actinomycosis  are  found  in  the 
cells,  which,  however,  do  not  assume  the  pro- 
nounced club  shape  seen  in  colonies  of  the  ray  fun- 
gus. 

Two  varieties  of  the  disease  are  laiown,  one  in 
which  the  granules  are  brown  or  black,  and  an- 
other in  which  they  are  white  or  yellowish;  the 
latter  is  encountered  much  more  frequently  than 
the  former. 


G34  INFECTION     AND     IMMUNITY. 

Pure  cultures  of  the  organism,  which  is  callel 
Streptothrix  maduros  (Vincent),  were  first  ob- 
tained by  Vincent  in  1894,  and  have  been  studied 
by  a  number  of  observers  since  that  time.  It  bears 
a  close  resemblance  to  the  actinomyces  and  by  some 
is  considered  a  variety  of  this  organism.  Differ- 
ences between  the  black  and  white  varieties  are  not 
clearly  set  forth.  The  disease  occurs  in  southern 
Asiatic  countries,  in  northern  Africa,  and  in  the 
United  States  (rare). 

VII.  INFECTIONS  BY  STREPTOTHRIX^  CLADOTHRIX 
AND  LEPTOTHRIX. 

streptotiirix  Culturcs  of  strcptothrix,  differing  from  the 
actinomyces,  have  been  obtained  from  the  lungs 
in  a  number  of  instances  and  in  various  countries. 
They  have  been  found  in  such  lesions  as  broncho- 
pnerxmonia,  or  more  extensive  consolidation  of  the 
lungs,  and  in  cases  of  empyema.  In  other  instances 
organisms  which  have  been  classed,  some  as  strep- 
tothrix, others  as  cladothrix,  have  been  cultivated 
from  processes  which  resembled  actinomycosis. 

Nocard  considers  a  streptothrix  as  the  cause  of 
farcin  du  boeuf  (farcy  of  cattle),  a  disease  encoun- 
tered especially  in  the  countries  of  southern  Eu- 
rope, and  similar  organisms  have  been  cultivated 
from  suppurating  or  granulomatous  foci  in  other 
animals. 

Leptothrix  huccalis,  a  thread-like  organism 
which  does  not  form  branches  and,  hence,  is  not  an 
actinomyces  nor  a  streptothrix,  is  frequently  found 
as  a  saprophytic  organism  in  the  mouth  cavity,  and 
a  similar  fungus,  Leptothrix  vaginalis,  has  been 
encountered  in  the  vagina.  Although  organisms 
of  this  type  are  relatively  harmless,  they  have  occa- 


OIDIOMYCOSIS. 


035 


sionally  been  found  in  diseased  conditions  of  the 
tonsils  and  pharynx. 

VIII.    OIDIOMYCOSIS. 

In  1894  Gilchrist  described  a  skin  disease,  which 
has  since  been  known  as  blastomycetic  dermatitis, 
or  blastomycosis  or  oidiomycosis  of  the  skin.  From 
a  second  case  he  cultivated  a  fungus  which  at  first 
he  was  inclined  to  consider  as  an  oidium,  but  later 
called  a  blastomyces.  Since  that  time  many  simi- 
lar cases,  especially  in  Chicago  and  the  adjacent 
territory,  have  been  discovered  and  reported  by 
Wells,  Hektoou,  ITyde  and  Montgomery,  Eicketts 
and  others.  Tn  many  instances  the  specific  fungi 
have  been  cultivated. 

Further  investigations  by  Eixford  and  Gilchrist, 
Basse,  Curtis,  ITyde  and  Montgomery  and  others 
have  brought  to  light  the  existence  of  systemic 
infections  by  fungi  which  are  identical  with  those 
found  in  blastomycetic  dermatitis,  and  cases  in 
which  the  disease  primarily  was  limited  to  the 
skin  have  gone  on  to  generalized  infection.  The 
converse  is  also  true,  that  infections  which  pri- 
marily are  systemic,  or  rather  pulmonary,  give  rise 
to  secondary  invasion  of  the  skin  in  a  large  per- 
centage of  the  cases.  Busse  and  Curtis  both  de- 
scribed infections  with  these  organisms  as  8ac- 
charomycosis  hominis,  on  account  of  the  fermenta- 
tive powers  of  the  organisms  concerned.  Sacclia- 
romycosis  liojninis,  blastomycetic  dermatitis  and 
generalized  blastomycosis  are  identical  processes 
pathologically  which  have  as  their  cause  a  group  of 
fungi,  the  individual  strains  of  which  may  show 
considerable  differences.     A  similar  disease  which 


"Blastomy- 
cetic" Der- 
matitis. 


Systemic 
Olcliomyeosls. 


636  l^FEGTIOlS'     AAD     IMMUNITY. 

has  been  observed  in  South  American  States  and 
in  California  was  formerly  considered  as  a  proto- 
zoic  infection,  but  Ophlils  and  Moffitt  have  shown 
that  this  disease  also  is  caused  by  a  fungus  which 
has  man}'  points  of  similarity  with  the  organisms 
of  local  and  systemic  blastomycosis. 

The  number  of  observed  cases  of  systemic  blas- 
tomycosis has  increased  greatly  of  late.  Twenty- 
four  have  been  reported,  and  of  these  18  or 
19  are  known  to  have  proved  fatal;  three  appear 
to  have  recovered  spontaneously  or  under  treat- 
ment, especially  with  potassium  iodid  or  cop- 
per sulphate  (Bevan).  That  the  disease  has  often 
been  passed  over  for  systemic  tuberculosis  seems 
very  probable  (one  such  case  is  known),  and  that 
it  is  much  more  common  than  usually  supposed  is 
indicated  by  the  recognition  of  five  cases  in  the 
wards  of  the  Cook  County  Hospital  (Chicago)  by 
Stober  and  others  from  June  until  January  of 
1907. 
Nature  of  In  blastomycetic  dermatitis  and  systemic  blas- 
tomycosis, the  fungi  proliferate  in  the  tissue  by 
budding,  and  are  found  chiefly  in  the  intra-epi- 
thelial  and  subcutaneous  abscesses,  and  in  the 
granulation  tissue,  nodules  and  abscesses  of  inter- 
nal organs.  Their  appearance  in  culture  media 
and  their  biologic  properties  are  subject  to  consid- 
erable variations,  at  one  time  growing  as  a  mold, 
at  another  time  more  like  the  typical  oidium,  and 
again  resembling  some  form  of  3'east.  Eicketts 
considers  that  the  genus  oidium  is  sufficiently 
broad  to  include  all  the  types  which  have  been 
described,  and  that  the  term  blastomyces  is  too 
narrow.     He  applies  the  name  of  Oidiomycosis  to 


Fungi. 


PATHOLOGY     OF    BLASTOMYCOSIS.         637 

the  disease.  The  organisms  which  have  been  cul- 
tivated from  the  cases  in  California  grow  as  molds, 
and  they  differ  from  those  described  by  Gilchrist, 
Hektoen,  Eicketts  and  others  in  that  they  form 
endospores  and  apparently  do  not  bud  in  the  tis- 
sues of  the  host  (Ophiils,  Wolbach).  This  feature 
is  so  constant  that  it  would  seem  to  constitute  a 
specific  difference  between  these  organisms  and 
those  found  in  blastomycosis.  There  are  reasons 
for  believing,  however,  that  endospore  formation 
is  a  facultative  property  of  at  least  some  of  the 
organisms  of  blastomycosis  (LeCount  and  Myers), 
and  if  this  proves  to  be  true,  the  two  groups  are 
brought  very,  close  together  biologically  as  well 
as  morphologically.  Ophiils  calls  this  parasite 
Oidium  coccidiades,  agreeing  with  Eicketts  as  to 
the  generic  character  of  the  group,  and  the  cor- 
responding disease  bears  the  name  of  coccidiodal 
granuloma. 

The  skin  infection  in  both  diseases  usually  ap-  Pathology. 
pears  as  a  coarse  warty  and  ulcerative  lesion,  in 
which  the  large  papillae  and  cutaneous  areola  are 
beset  with  minute  abscesses;  the  process  extends 
gradually  and  eventually  may  involve  large  areas. 
Microscopically,  the  tissue  shows  an  enormous  epi- 
thelial hyperplasia  with  intraepithelial  abscesses, 
and  a  richly  cellular,  granulomatous  condition  of 
the  subepithelial  tissue,  in  which  giant  cells  and 
small  abscesses  are  found.  When  the  disease  is 
systemic,  various  organs,  especially  the  lungs, 
spleen  and  kidneys,  skin  and  joints,  are  the  seats 
of  abscesses  and  nodules  which  contain  the  para- 
sites in  immense  numbers,  and  many  giant  cells 


638  INFECTION     AXD     IMMUNITY. 

of  the  Langhans  type.     The  lungs  sliow  lobular 
or  more  extensive  consolidation. 

The  l3anph  glands  show  little  involvement  in 
blastomycosis;  it  is  believed  that  metastases  usu- 
ally take  place  through  the  blood  stream,  which 
may  depend  on  tlie  large  size  of  the  organisms. 
On  the  other  hand,  there  is  marked  lymphatic 
involvement  in  coccidioidal  granuloma,  and  it  is 
probable  that  the  liberation  of  minute  endospores 
favors  lymphatic  metastasis.  Pathologically,  the 
two  diseases  seem  to  be  differentiated  somewhat 
by  the  fact  that  coccidioidal  granuloma  presents 
a  greater  degree  of  necrosis  and  caseation  than 
blastomycosis,  and  the  lesions  in  the  former  bear 
a  closer  resemblance  to  tuberculosis  than  do  those 
of  blastomycosis  (Hektoen).  The  differences, 
however,  seem  to  be  in  degree  rather  than  in  kind, 
indicating  a  certain  lack  of  correspondence  in  the 
pathogenic  properties  of  the  organisms  concerned. 
Infection  The  sldn  infection  occasionally  follows  slight 
traumatism,  while  in  other  instances  no  predispos- 
ing condition  is  known  by  the  patient.  The  occur- 
rence of  cutaneous  lesions  in  crops  has  been  noted, 
and  suggests  that  in  some  instances  they  may  orig- 
inate as  embolic  foci  from  a  pulmonary  lesion 
which  later  heals  or  becomes  latent.  In  the  sys- 
temic infection  the  primary  lesion  appears  to  be 
in  the  lungs  in  most  cases,  from  which  the  bleed 
and  other  organs,  including  the  skin,  may  be  in- 
vaded. Pulmonary  oidiom3^cosis  simulates  pul- 
monary tuberculosis.  In  extensive  involvement  of 
the  lungs  the  organisms  may  be  demonstrated  in 
the  sputum. 


Atria. 


THRUSH.  639 

At  present,  little  is  known  concerning  immu- 
nity to  these  infections.  Eicketts  prepared  a  vac- 
cine by  disintegrating  the  organisms  in  a  ball- 
mill,  and  in  collaboration  with  Eggers  found  that 
the  immunization  of  animals  with  the  vaccine 
causes  the  formation  of  agglutinating  or  precipi- 
tating antibodies  (from  unpublished  experiments) . 
The  practical  value  of  the  vaccine  has  not  had  a 
thorough  trial.  Christensen  and  Hektoen  used 
it  in  two  cases  of  systemic  blastomycosis  which, 
however,  were  so  far  advanced  that  no  conclusions 
as  to  the  value  of  the  treatment  could  be  drawn. 
Theoretically,  the  conditions  would  seem  to  be 
favorable  for  the  vaccine  treatment  of  blastomy- 
cosis, since  the  disease  is  of  a  chronic  character 
and  there  is  little  opportunity  for  autoimmuniza- 
tion  on  account  of  the  dense  capsule  which  sur- 
rounds the  organisms.  By  grinding  the  organ- 
isms up,  their  constituents  may  be  injected  in 
such  condition  that  they  are  readily  absorbed. 

Thrush. 

Ophlils  very  properly  suggests  that  thrush 
should  be  considered  as  one  form  of  oidiomycosis. 
Thrush  is  of  particular  interest  because  of  the  early 
date  at  which  its  parasitic  nature  was  recognized. 
Langenbeck  and  Berg,  in  1839  and  1841,  are  cited 
as  the  discoverers  of  the  fungus,  and  they  repro- 
duced the  disease  by  inoculations  with  fragments 
of  the  membrane.  The  parasite  was  studied  a  little 
later  by  Grub}-,  Eobin  and  others,  and  the  latter 
gave  it  the  name  of  Oidium  albicans.  Grawitz  ob- 
tained it  in  pure  culture  in  1877  and  demonstrated 
its  pathogenicity  for  dogs  and  rabbits. 


Systemic 


640  INFECTION     AND     IMMUNITY. 

Cultures^  of  the  organism  show  differences  in 
size,  morphology,  chemical  activities  and  methods 
of  proliferation,  although  the  variations  are  hardly 
so  wide  as  those  found  among  the  fungi  cultivated 
from  cases  of  'blastomycosis/' 
Infection.  Although  thrush  usually  is  considered  a  rather 
harmless  affection,  Yirchow  long  ago  showed  that 
its  filaments  may  penetrate  the  submucous  tissues 
and  even  the  lumens  of  blood  vessels.  In  rare  in- 
stances systemic  infection,  with  abscesses  in  the 
brain,  kidney  and  spleen  or  with  nodules  in  the 
lungs,  has  been  noted;  in  these  cases  the  condi- 
tions resemble  those  found  in  systemic  "blastomy- 
cosis." 

The  healthy  person  has  little  or  no  susceptibility 
to  thrush,  although  a  few  cases  of  infection  have 
been  noted  in  individuals  who  were  otherwise  nor- 
mal. Customarily  it  attacks  only  those  who  are 
in  a  low  state  of  vitality,  as  poorly  nourished  chil- 
dren or  those  in  advanced  age,  or  those  whose  re- 
sistance is  much  lowered  by  some  other  disease  (ty- 
Phagocytosis  phoid,  diabetes,  etc.). 

Phagocytosis  of  yeast  and  oidium-like  cells  takes 
place  when  they  are  placed  in  the  abdominal  cav- 
ity of  experiment  animals  (guinea-pigs).  A  num- 
ber of  leucocytes  may  fuse  to  form  a  plasmodial 
mass  around  one  or  more  of  the  parasitic  cells. 
Roger  and  Noisette  caused  an  increase  in  the  re- 
sistance of  rabbits  to  thrush  infection  by  the  intra- 
venous injection  of  small  doses  of  the  parasite.  Ac- 
cording to  Noisette,  an  immune  serum  agglutinates 
only  the  strain  used  in  the  immunization. 

Infections  of  other  animals  (horses,  cattle)  by 
oidium-like  organisms,  the  trichophyton  and  other 
fungi  which  cause  superficial  diseases  in  the  skin 


and    Immu- 
nity. 


ASPERGILLUS.  641 

of  man,  and  other  fungi  (aspergillus,  mucor), 
which  occasionally  are  pathogenic  for  man,  will  not 
be  discussed. 


CHAPTER  XXVIII 
GROUP  V. 


DISEASES  DUE  TO  SPIIJILLA. 
I.     RELAPSING   FEVER. 

Tiie  Organ-  In  1868,  Obermeier  discovered  in  the  blood  of 
patients  suffering  from  relapsing  fever,  "Very  fine 
threads  exhibiting  motility/^  These  "threads" 
have  since  been  known  as  the  Spirillum  obermeieri^ 
and  are  recognized  as  the  cause  of  the  disease. 
Xovy  describes  two  forms  of  the  organism.  The 
short  forms  var}^  from  7  to  9  microns,  and  are 
about  0.25  microns  in  width.  The  long  forms  vary 
from  16  to  19  microns.  They  result  from  processes 
of  agglutination  or  multiplication.  The  organism 
is  provided  at  one  end  with  a  long  flagellum.  The 
turns  of  the  spirals  of  the  short  forms  are  two  or 
three  in  number.  Tlie  spirilla  are  very  motile, 
and  not  only  move  from  place  to  place  but  rotate 
on  the  long  axis. 

1.  The  spirillacse,  Migula's  third  family  under  the 
Order  of  Eubacteria,  comprises  organisms  with  these  char- 
actei'istics  :  "Cells  which  are  twisted  screw-fashion  or  repre- 
sent a  segment  of  a  spiral.  Division  takes  place  only  in  one 
direction  of  space  after  the  cell  has  elongated."  The  dif- 
ference between  spirillum  and  spirochseta  is  shown  by  the 
following :  "3,  Genus :  Spirillum.  Cells  rigid,  with  polar 
tufts,  for  the  most  part  bent  in  the  form  of  a  half-circle, 
as  organs  of  locomotion.  4.  Genus  :  Spirochaeta.  Cells  with 
snake-like  bending,  organs  or  locomotion  unknown." 
Although  Migula  classes  this  organism  with  the  bacteria, 
there  is  some  ground  for  considering  it  protozoon  in  nature. 
According  to  Novy,  the  organism  of  relapsing  fever  has  a 
rigid  cell  body  with  an  end  flagellum  and  would  therefore  be 
be  classed  as  a  spirillum. 


RELAPSING     FEVER.  643 

The  organism  has  not  been  grown  artificially, 
but  it  may  be  kept  alive  for  a  number  of  days  in 
the  blood  or  serum  of  patients.  As  the  micro-or- 
ganisms die,  agglomerations  are  formed  and  they 
undergo  granular  changes. 

The  organism  is  not  found  in  Nature,  and, 
since  it  occurs  only  in  the  blood  of  the  sick,  it  has 
long  been  assumed  that  infection  can  be  accom- 
plished only  by  the  inoculation  of  infected  blood. 
The  parasites  have  been  demonstrated  repeatedly 
in  bedbugs  which  are  found  on  the  mattresses  of 
the  sickbed,  and  monkeys  have  been  infected  by 
inoculating  them  with  the  blood  found  in  the 
bodies  of  these  insects,  and  by  the  bites  of  the  lat- 
ter (Tictin).  It  is  said  that  they  may  remain 
alive  in  bedbugs  for  as  long  as  thirty  days.  It  is 
not  altogether  excluded  that  other  vermin  also 
transmit  the  disease. 

The  spirochete  does  not  appear  in  any  of  the  ex- 
cretions, unless  these  happen  to  be  of  a  bloody 
character. 

Certain  monkeys,  those  belonging  to  the  slender- 
nosed  family  {Gatarrhince) ,  may  be  infected  by 
injecting  the  blood  of  patients,  provided  the  blood 
used  is  taken  during  the  paroxysm,  i.  e.,  at  a  time 
when  the  microbes  are  known  to  be  in  the  blood. 
Novy  has  found  that  the  disease  can  be  readily 
transmitted  to  white  rats  and  mice;  rabbits  and 
guinea-pigs  appear  to  be  refractory.  In  mice,  as 
in  monkeys  and  man,  relapses  occur  regularly. 
In  rats,  however,  immunity  is  established  after 
one  attack.  The  incubation  period  in  man  usually 
is  from  five  to  seven  days,  and  in  monkeys  from 
one  and  one-half  to  four  days.     Cloudy  swelling 


644  INFECTION     AND     IMMUNITY. 

of  the  parench3TQatous  organs,  ecch3^moses  and 
infarcts  of  the  spleen  and  kidneys  are  found  in 
fatal  cases. 

Prophylaxis  consists  in  isolation  of  the  patient, 
cleanliness,  and  the  destruction  of  vermin,  espe- 
cially bedbugs. 

Relapsing  fever  occurs  in  various  races  of  man, 
and  so  far  as  known  none  is  immune. 
immnnitF.  ^g  stated  abovc,  a  remarkable  feature  in  the 
,  course  of  the  disease  is  .the  rapidity  with  which  the 
micro-organisms  disappear  from  the  blood  at  the 
time  of  the  crisis.  Metchnikoff  refers  this  to 
phagocytosis  by  the  microphages,  which  undergo 
a  progressive  increase  during  the  paroxysm  and 
decrease  after  the  crisis.  Very  little  phagocytosis 
appears  to  take  place  in  the  circulating  blood,  but 
in  the  spleen  many  spirochetes  are  found  within 
polymorphonuclear  leucocytes. 

Tictin  also  found  the  spirochetes  in  the  paren- 
chymatous cells  of  the  kidney,  liver  and  lungs. 
Phagocytosis  is  most  marked  at  or  near  the  time 
of  the  crisis.  According  to  Metchnikoff,  relapse 
or  reinfection  is  accomplished  by  spirochaetse  which 
again  invade  the  body  from  the  spleen. 

According  to  Novy  and  Knapp,  two  distinct 
types  of  protecting  substances  develop  during  the 
course  of  the  disease.  They  describe  a  germicidal 
substance  which  causes  bacteriolysis  both  in  vitro 
and  as  observed  in  Pfeiffer's  phenomenon.  In  ad- 
dition to  this  germicidal  substance,  they  believe 
that  a  second  protecting  substance,  which  they 
term  the  immune  body,  is  present.    The  existence 


THEORY     OF    RELAPSES.  e45 

of  the  immune  body  is  established  by  the  fact  that 
passive  immunization  can  be  accomplished  by  the 
use  of  serum  having  no  germicidal  action.  Phago- 
cytosis is  concerned  chiefly  with  organisms  killed 
by  the  germicidal  agent.  Marked  agglutination 
occurs  with  immune  serum. 

The  immunity  conferred  by  an  attack  of  relaps- 
ing fever  is  probably  of  long  duration.  Other  ani- 
mals are  also  immune  to  a  second  infection. 

The  development  of  immune  bodies  which  oc-  Theory  of 
curs  with  the  first  febrile  period  is  insufficient  to 
cause  complete  destruction  of  the  spirilla.  A  few 
of  these,  aided  possibly  by  their  sheltered  location 
in  lymph  spaces,  survive  and  may  become  immu- 
nized to  some  extent  against  the  antibodies.  These 
organisms  by  multiplication  institute  a  second 
febrile  period  which  is  followed  by  a  higher  devel- 
opment of  immune  bodies.  Each  relapse  has  the 
effect  of  heightening  the  immunization  until  com- 
plete destruction  of  the  organisms  occur. 

Hereditary  immunity  may  result  from  intra-  Hereditary 
uterine  infection.  Spirilla  have  been  found  in  '"™°" 
the  heart's  blood  of  the  human  fetus.  Novy  and 
Knapp  describe  the  occurrence  of  both  active 
hereditary  immunity  occurring  in  the  young  of 
infected  rats  and  passive  hereditary  immunity  oc- 
curring in  the  young  of  rats  passively  immunized. 

It  is  evident  from  the  work  of  Novy  and  Knapp 
that  the  chief  difficulty  in  the  production  of  a 
curative  serum  is  that  of  the  cultivation  of  the 
spirillum.  It  may  be  possible,  however,  to  immu- 
nize larger  animals  with  infected  blood  and  thus 
obtain  an  efficient  antiserum. 


646  IXFECTIOX     AXD     IMMUNITY. 

In  addition  to  the  European  relapsing  fever 
there  are  at  least  three  recurrent  fevers  caused  by 
varieties  of  spirilla  distinct  from  one  another  in 
morphology  and  according  to  Kolle  and  Schatiloff 
in  complement  deviation.  One  of  these  three 
forms  occurs  in  India.  The  other  two  are  known 
as  African  tick  fever.  Of  these  two  forms,  that 
of  West  Africa  was  studied  by  Button  and  Todd. 
The  other  form  is  prevalent  in  East  Africa  and 
was  studied  by  E.  Koch.  According  to  Koch,  the 
ticks  which  carry  the  organisms  also  transmit 
them  to  the  eggs,  which  in  turn  develop  into  ticks 
capable  of  infecting  man.  Koch  found  spirilla  in 
only  a  part  of  the  eggs  of  infected  ticks. 

II.      SYPHILIS. 

Historical       It  is  impossible  here  to  describe  or  even  men- 

Datu. 

tion  the  many  cocci,  bacteria  and  protozoa  (?) 
which  have  been  brought  into  etiologic  relation- 
ship with  syphilis.  Until  recently,  the  bacillus  of 
Lustgarten  occupied  a  fairly  prominent  position 
as  the  possible  cause.  This  organism  resembles 
the  tubercle  bacillus  in  its  morphology  and  stain- 
ing properties,  and  is  not  to  be  differentiated  from 
one  of  the  smegma  bacilli.  Its  recognition  in 
syphilitic  lesions  has  always  been  difficult,  and  by 
far  the  greatest  number  of  investigators  have  been 
unable  to  demonstrate  it.  It  has  never  received 
general  recognition  as  the  cause  of  the  disease,  and 
its  presence  in  lesions  of  the  genitals  has  no  sig- 
nificance because  of  the  occurrence  of  smegma  bac- 
illi in  this  locality. 

The  bacillus  of  De  Lisle  and  Julien,  and  that 
of  Joseph  and  Piorkowski  rest  on  no  better  basis. 


SYPHILIS.  647 

In  1905,  Hoffman  and  Schaudinn  discovered  in  spirocha^ta 
the  primary  and  secondary  lesions  of  syphilis,  a 
very  delicate  spirochete  which  they  named  Spiro- 
chceta  pallida  on  account  of  the  difficulty  of  stain- 
ing it  with  anilin  dyes. 

The  spirillum  is  of  corkscrew-like  form  with 
froni  six  to  thirty  tarns.  It  is  ahout  1/4  rnicron  in 
thickness,  and  from  4  to  26  microns  in  length. 
The  turns  are  regular  and  deep  in  the  middle  and 
become  less  pronounced  toward  the  ends.  There 
is  a  fine  flagellum  at  each  end  of  the  spirillum. 
When  observed  in  serum  by  means  of  dark-field 
illumination,  the  organism  exhibits  marked  motil- 
ity. Movement  may  be  observed  both  forward  and 
backward;  rotary  and  bending  motion  is  also  seen. 
Stained  with  Giemsa's  eosinate  of  azur,  the  spirilla 
are  stained  a  pale  rose  color.  According  to  Schau- 
dinn, division  takes  place  longitudinally,  and  in 
this  respect  the  spirochete  resembles  the  trypan- 
osomas.  The  systematic  position  of  the  organism 
is  not  yet  certain.  Cultivation  has  been  reported 
by  a  number  of  workers.  The  cultures  were  not 
pure,  however,  and  the  spirochetes  were  non-viru- 
lent. 

The  Spirochceta  pallida  has  been  found  in  the  ^?a*9?*ic 

^  ^  Distribution. 

lesions  of  all  stages  of  syphilis.  These  organisms 
are  found  in  great  abundance-  in  the  primary  les- 
ion and  in  the  tissues  of  the  infected  regional 
lymph  glands.  They  are  easily  detected  in  the 
tissues  affected  in  secondary  syphilis.  Although 
found  in  the  circulating  blood,  they  occur  only 
occasionally  or  in  small  numbers.  In  the  organs 
affected  by  fetal  syphilis,  spirochetes  are  found  in 


648 


INFECTION     AND     IMMUNITY. 


Experiments 

of  Metclinikon 

and  Rons. 


Transmission 

from  Monkey 

to  Monkey. 


great  abundance.  In  tertiary  syphilis  the  lesions 
contain  only  a  few  organisms.  Those  present  are 
most  numerous  in  the  tissues  surrounding  the 
necrotic  center. 

It  occurred  to  Metchnikoff  and  Eoux  as  it  had 
occurred  to  others  that  the  monkey,  particularly 
the  higher  species  (chimpanzees),  should  on  ac- 
count of  their  biologic  proximity  to  man,  be  the 
most  suitable  animal  for  the  production  of  experi- 
mental syphilis.  Attention  has  already  been  called 
to  this  proximity  as  indicated  by  the  reaction  of 
serum  precipitins. 

Their  first  inoculation  was  performed  on  a  fe- 
male chimpanzee,  virus  from  a  primary  lesion  and 
from  mucous  patches  being  introduced  by  means 
of  scarification  into  the  prepuce  of  the  clitoris  and 
into  the  skin  of  the  eyebrow.  The  wounds  healed, 
and  twenty-six  days  after  inoculation  a  vesicle 
which  soon  was  surrounded  by  induration  appeared 
on  the  prepuce.  This  lesion  was  pronounced  a  typi- 
cal hard  chancre  by  eminent  dermatologists  and 
syphilologists.  With  the  appearance  of  the  chan- 
cre the  inguinal  lymph  glands  became  enlarged^ 
and  one  month  later  a  papular  eruption  appeared 
on  the  thighs,  abdomen  and  back.  The  papules 
persisted  for  more  than  a  month,  and  were  still 
discernible  when  the  animal  died  several  weeks 
later  of  pneumococcus  infection.  Before  this  ani- 
mal died  a  second  chimpanzee  was  inoculated  from 
the  primary  and  secondary  lesions  of  the  first  ani- 
mal, resulting  in  the  development  of  primary  le- 
sions and  of  adenitis.  Still  another  successful  in- 
oculation resulted  in  secondary  lesions  with  the 
formation  of  mucous  plaques.  These  observers 
have   since  performed  many  similar  experiments 


SYPHILIS     IN     ANIMALS.  649 

with  positive  results,  when  the  higher  types  of 
monkeys  were  used.  Confirmation  has  come  from 
a  number  of  independent  experimenters  (e.  g., 
Lassar,  A.  Neisser,  Kraus,  Flexner),  and  A.  Neis- 
ser  in  particular  has  taken  up  the  work  on  an 
extensive  scale. 

Some  of  Neisser's  work  is  of  the  utmost  impor-  Experiments 

m-^  of  ^icisscr 

tance.  The  experiments  of  Metchnikoff  and  Eoux 
had  already  indicated  that  the  higher  monkeys 
(chimpanzee,  etc.)  acquired  generalized  syphilis 
more  readily  than  the  lower  species.  Neisser's 
work  corroborates  this,  and  he  recognizes  a  scale  of 
susceptibility  which  corresponds  roughly  with  the 
proximity  of  the  different  species  to  man,  as  indi- 
cated by  general  morphology  and  the  reaction  of  ^ 
serum  precipitins.  The  chimpanzee,  orang-utan 
and  gorilla  are  the  most  susceptible,  and  the  syph- 
ilis produced  in  them  approaches  closely  that  seen 
in  man,  including  the  secondary  symptoms.  It  is 
suspected  that  the  cynocephalus  varieties  are  less, 
and  the  macacus  varieties  least  susceptible.  Among 
the  macaci  the  smaller  types  (rhesus)  are  more 
resistant  than  the  larger.  The  lower  susceptibility 
of  these  animals  is  recognized  by  the  failure  of 
secondary  symptoms  to  develop,  hence  in  them  the 
syphilis  may  be  purely  local  (Neisser).  Spiro- 
chetes have  been  found  in  all  the  lesions  of  experi- 
mental syphilis  in  monkeys. 

Bertarelli  first  succeeded  in  producing  experi-  sypiiiiis 
mental  syphilitic  keratitis  in  the  rabbit  and  found  A^iimafJ'. 
associated  with  it  the  Spirocliceta  pallida.  His 
work  has  been  verified  by  various  observers.  Miih- 
lens  and  others  have  been  able  to  produce  a  pri- 
mary lesion  in  the  guinea-pig  by  material  takoii 
from  syphilitic  keratitis  in  the  rabbit. 


650  IXFECTIOX     AXD     IMMUNITY. 

spirochaeta  The  fourth  postulate  of  Koch,  that  of  cultiva- 
tbe  ^'ans^  of  tion  in  pure  culture  and  reproduction  of  the  dis- 
sypbiiis.  g^g^  i^y  means  of  such  pure  cultures,  has  not  yet 
been  carried  out.  The  occurrence  of  the  organism 
as  described  has,  however,  been  such  strong  evi- 
dence that  the  Spirochceta  pallida  is  accepted  as 
the  cause  of  s^'philis. 
Infection.  Infection  usually  is  venereal.  It  is  not  defi- 
nitely known  whether  a  defect  of  the  surface  of  the 
prepuce,  glans,  vagina,  etc.,  is  essential  for  infec- 
tion. The  epithelium  in  these  localities  is  so  deli- 
cate that  defects  of  microscopic  dimensions  may  be 
easily  produced,  and  infection  may  take  place 
through  such  defects  as  through  grosser  lesions.  It 
is  well  Ivnown  that  the  lip,  tongue,  conjunctiva  and 
finger  may  be  the  seats  of  primary  lesions,  and  it 
is  probable  that  no  part  of  the  body  surface  is 
immune  when  the  virus  is  introduced  suitably. 
vimience.  CHnical  experience  indicates  that  the  virulence 
of  the  Spirochceta  pallida  is  not  uniform.  It  is 
possible  that  certain  strains  are  more  likely  to 
bring  about  ^^post-syphilitic*'  diseases  than  others. 
That  the  resistance  of  the  organism  outside  the 
body  is  low  seems  evident  from  the  fact  that  trans- 
mission is  practically  unknown  except  as  it  occurs 
by  direct  contact.  Xeisser  destroyed  it  by  heating 
to  60°  C.  for  thirty  minutes,  but  at  this  tempera- 
ture for  ten  to  twenty  minutes  its  virulence  for 
monkeys  was  retained. 

Prophylaxis  demands  no  principles  not  generally 
known. 

Susceptibility  to  syphilis  varies  a  great  deal,  not 
in  the  sense  that  some  are  immune,  but  in  that  a 
more  virulent  type  of  disease  develops  in  some  than 
in  others.     This  is  a  condition,  however,  which 


IMMUNITY     IN     SYPHILIS.  G51 

is  difficult  to  differentiate  from  variations  in  the 
virulence  of  the  infecting  agent.  Syphilis  is  said 
to  be  particularly  virulent  when  introduced  into 
a  race  of  people  for  the  first  time. 

There  is  no  reason  to  believe  that  natural  im-  immunity. 
munity  to  syphilis  exists  in  man.  It  was  formerly 
believed  that  the  fact  that  many  prostitutes  who 
were  exposed  to  syphilis  over  a  considerable  length 
of  time  and  who  at  no  time  showed  active  symp- 
toms, were  immune  to  the  disease.  The  finding 
of  positive  Wassermann  reactions  in  a  large  per- 
centage of  such  individuals  would  indicate,  how- 
ever, that  they  did  acquire  syphilis.  Through  the 
application  of  the  Wassermann  test,  it  has  also 
been  shown  that  the  laws  of  Colles  and  Profeta 
are  also  incorrect.  The  former  states  that  the 
mother  who  gives  birth  to  a  syphilitic  child  Avith- 
out  herself  showing  signs  of  the  disease,  is  immune 
to  syphilis.  Knopf  elm  acher  and  Lehndorf  ob- 
tained positive  Wassermann  reactions  in  56  per 
cent,  of  such  mothers.  Profeta's  law  states  that  a 
healthy  child,  born  of  a  syphilitic  mother,  can 
suckle  the  mother  without  becoming  infected.  In 
this  case  many  of  the  so-called  healthy  children 
have  been  found  to  be  syphilitic,  and  others  which 
were  actually  non-syphilitic  have  been  observed  to 
contract  the  disease  from  the  mother. 

Kegarding  second  infections,  experiments  on 
apes  have  shown  that  second  infections  are  readily 
produced  at  any  time  after  the  primary  lesion  has 
developed.  Such  infections  are  possible  even  after 
thorough  courses  of  treatment  terminating  in  re- 
covery. These  second  infections  differ  from  the 
first  in  that  the  incubation  period  is  shorter  and 


652  IXFECTION     AND     IMMUNITY. 

the   course   of   development   and   healing   of   the 
lesion  is  more  rapid. 

Apes  with  tertiary  syphilis  react  (according  to 
Finger)  to  inoculation  with  syphilitic  material, 
with  the  formation  of  tertiary  lesions. 

Finger  conceives  of  the  process  of  immunity  in 
syphilis  as  similar  to  the  phenomenon  of  allergy 
of  V.  Pirquet.  That  is  in  a  variation  in  the  capa- 
bility of  reaction  without  the  establishment  of 
non-susceptibility.  Second  infections  with  syphilis 
have  also  been  observed  clinically. 
Seroreaction       ^he   scrum   reaction  is   discussed  fullv   in   the 

and  Sero-  _  ^ 

tiierapy.  chapter  on  complement  deviation. 

The  eflficiency  which  is  promised  by  the  recent 
preparation  of  Ehrlich,  known  as  salversan,  leaves 
but  little  to  be  desired  as  a  therapeutic  agent.  The 
lack  of  production  of  immunity  also  renders  the 
possibility  of  a  curative  serum  very  doubtful. 

III.     FRAMBESIA. 

Frambesia  or  yaws  is  a  tropical  disease  found 
in  both  hemispheres.  Castellani  found  a  spirillum 
associated  with  the  lesions  which  corresponds  mor- 
phologically with  the  SpirochfEta  pallida.  Owing 
to  this  similarity  in  the  organisms,  and  to  the 
fact  that  yaws  resembles  syphilis  clinically,  the 
two  have  been  considered  as  different  forms  of  the 
same  disease.  Castellani,  however,  finds  that  in 
the  complement  deviation  reaction  neither  anti- 
gen nor  antibody  can  be  used  interchangeably.  He 
considers  the  two  spirochetes  as  distinct  from  each 
other  and  names  the  spirochete  of  yaws,  Spiro- 
chceta  pertenuis.  Transmission  occurs  by  direct 
contact  and  probably  also  by  means  of  flies. 


OTHER     SPIROCHETES.  G53 

IV.    OTHER  SPIROCHETES. 

Among  other  pathogenic  spirilla  may  be  men- 
tioned Spirochwta  anserina,  of  the  spirillosis  of 
geese,  Spirochcsta  gallinarun,  causing  a  fatal  dis- 
ease of  chickens  and  S.  Theileri,  found  in  a  disease 
of  cattle  in  Africa.  The  last  two  are  transmitted 
bv  ticks. 


CHAPTER    XXIX. 
GROUP  VI. 


PROTOZOON    INFECTIONS. 
I.    MALARIA. 

Etiology.  The  etiology  of  malaria,  which  for  long  was 
supposed  to  be  associated  with  impure  and  swampy 
atmospheres  (malaria  is  from  maP  aria,  Italian, 
meaning  bad  air),  remained  unknown  until  1880, 
when  Laveran  discovered  ameboid,  half-moon 
shaped  and  flagellated  forms  of  a  parasite  in  the 
blood  of  the  patients.  In  following  years  Golgi, 
Grassi,  Marchiafava  and  Celli  and  many  others 
took  prominent  parts  in  working  out  the  different 
forms  of  parasites,  their  sexual  characters  and  their 
relation  to  the  different  types  of  malaria. 
Ross  and  The  couccption  that  mosquitoes  may  be  influen- 
tial in  transmitting  malaria  is  a  very  old  one  and 
its  origin  is  unknown.  In  1894  Manson  suggested 
that  the  malarial  organism  may  utilize  the  mos- 
quito as  an  intermediate  host  where,  after  under- 
going further  development,  it  again  becomes  in- 
fectious for  man.  He  was  inclined  to  think  that 
the  flagella  are  reproductive  forms,  which  are 
^  essential  for  an  extra  corpus  life  of  the  parasite. 

The  proof  of  this  came  from  MacCallum  in  1897, 
who  showed  that  the  flagellated  forms  are  really 
spermatozoites,  the  function  of  which  is  to  im- 
pregnate female  cells  of  the  parasite.  This  was 
observed  first  in  relation  to  halteridium,  one  of 


MALARIA. 


655 


the  organisms  of  avian  malaria,  and  later  in  rela- 
tion to  the  parasites  of  human  malaria. 

In  the  same  year  Ross  found  the  pigmented, 
half-moon  shaped  parasites  of  sestivo-autumnal 
fever  in  the  stomach  of  the  anopheles  mosquito. 
Through  the  work  of  Ross  and  others  it  is  now 
established  that  the  malarial  parasite  undergoes 
further  development,  a  sexual  cycle,  in  anopheles, 
and  that  man  is  inoculated  only  by  the  bites  of 
such  infected  insects.  From  the  standpoint  of 
the  zoologist,  man  is  an  intermediate  host  for  the 
parasite,  since  the  latter  undergoes  its  higher  de- 
velopment only  after  it  reaches  the  mosquito. 

The  malarial  parasites  of  man  belong  to  the 
class  of  Sporozoa;  order,  Coccidiomorpha;  family, 
Hemosporidia ;  genus,  Plasmodium.  The  follow- 
ing are  the  names  given  to  the  three  species :  1. 
Plasmodium  prcecox  (parasite  of  sestivo-autumnal 
fever)  ;  2.  Plasmodium  vivax  (of  tertian  fever)  ; 
3.  Plasmodium  malarice  (of  quartan  fever). 

When  the  blood  of  one  suffering  from  tertian 
fever  is  examined  at  the  end  of  the  febrile  parox- 
ysm, or  at  the  beginning  of  the  afebrile  stage,  the 
parasites  are  found  within  the  erythrocytes  as  pale, 
rather  clear  bodies,  about  one-fifth  the  diameter  of 
the  corpuscle,  and  in  fresh  specimens  showing  an 
active  ameboid  movement.  They  are  v^y  difficult 
to  recognize  in  unstained  specimens.  They  increase 
in  size  gradually,  and  after  eighteen  hours,  when 
they  begin  to  acquire  pigment,  they  are  recognized 
more  easily.  After  twenty-four  hours  the  pig- 
ment has  increased  markedly  and  the  erythrocytes 
are  swollen  and  pale.  In  stained  preparations  the 
periphery  of  the  parasite  stains  more  deeply  than 
the  center  and  gives  it  a  pronounced  ring  form. 


Species   of 
Plasmodiuiu. 


Tertian 
Fever. 


650 


INFECTION     AND     IMMUNITY. 


Segmentation 

of  Asexnal 

Cells. 


Sexnal 
Cells. 


At  the  end  of  thirty-six  hours  they  have  increased 
noticeably  in  size  and  their  ameboid  motion  is 
less.  Shortly  before  the  next  attack — i.  e.,  from 
forty-six  to  forty-eight  hours  after  the  preceding 
one — the  pigment  assembles  into  one  or  two  groups 
in  the  center  of  the  parasite  and  clear  hyaline 
points  begin  to  appear.  These  are  the  young  endo- 
cellular  parasites  which  are  formed  by  division  of 
the  nucleus  of  the  mother  cell.  They  gradually 
increase  in  size  and  number,  and  a,-  the  red  cor- 
puscles disintegrate  they  are  discharged,  from  fif- 
teen to  twenty-five  in  number,  as  young  parasites. 
This  completes  the  cycle,  an  asexual  cycle,  which 
has  lasted  forty-eight  hours,  and  the  young  forms 
then  begin  a  new  cycle  after  penetrating  other  red 
corpuscles.  The  mother  cell  is  called  the  sporo- 
cyte  and  its  offspring  are  merozoites,  and  the  proc- 
ess of  division  schizogony. 

In  addition  to  the  asexual  cell  just  described, 
two  sexual  cells,  a  male  and  a  female,  grow  to 
adult  size  in  the  erythrocytes,  acquire  pigment  and 
eventually  become  free.  They  differ  from  the 
asexual  cell  in  that  the  pigment  continues  to  be 
uniformly  distributed,  and  neither  gives  rise  to 
young  parasites  by  division.  The  male  cell  (micro- 
gametocyte,  8-9  microns)  has  a  clear  protoplasm 
and  is  smaller  than  the  female  (macrogamete, 
10-14  microns)  ;  the  female  has  a  granular  proto- 
plasm. There  are  many  more  male  than  female 
cells.  They  undergo  no  further  development  in 
the  body  of  man,  and  in  order  that  the  sexual  pro- 
cess be  completed  the  two  cells  must  first  gain 
entrance  into  the  stomach  of  the  female  anopheles 
mosquito. 


MALARIAL     PARASITE. 


657 


A  further  step  in  the  sexual  process  may  be  seen 
in  drop  preparations  of  the  bloody,  although  this 
step  does  not  occur  in  the  human  body.  From  ten 
to  twenty  minutes  after  such  a  preparation  has 
been  made  the  male  cells^  after  a  period  of  agi- 
tation, discharge  from  four  to  eight  long,  thin 
flagella  (microgametes  or  spermatozoa),  which 
thrash  about  violently  and  eventually  come  in  con- 
tact with  a  female  cell,  which  they  enter  and  be- 
come unrecognizable. 

This  same  process  is  instituted  and  completed 
(sporogony)  in  the  stomach  of  the  mosquito,  the 
penetration  of  the  female  cell  by  the  spermatozoon 
resulting  in  the  impregnation  of  the  former.  Fol- 
lowing impregnation,  the  female  cell  gradually 
assumes  a  worm-like  or  sickle  shape  (ookinet), 
penetrates  the  wall  of  the  stomach  and  becomes 
encapsulated  (oocyst).  Forty-eight  hours  after 
the  mosquito  has  sucked  malarial  blood  all  the 
female  cells  have  reached  this  stage  and  no  more' 
free  parasites  are  found  in  the  stomach. 

About  five  days  after  the  blood  was  taken  the 
oocyst  has  increased  in  size  about  six  times  and 
has  formed  within  itself  a  number  of  small 
spheres,  which  are  called  daughter  cysts  or  sporo- 
blasts.  The  latter  soon  acquire  a  finely  striated  ap- 
pearance, which  is  due  to  the  formation  of  hun- 
dreds of  "germinal  rods"  or  sickle-like  bodies 
(sporozoites).  The  latter  are  nothing  less  than 
young  malarial  parasites,  which  are  thrown  into 
the  body  cavity  by  the  rupture  of  the  oocyst,  and 
are  carried  to  the  salivary  glands  of  the  mosquito 
by  the  lymphatic  circulation.  If  the  mosquito  has 
been  kept  at  a  temperature  of  24°  to  30°  C.  these 
sickle  forms  first  appear  in  the  salivary  gland  after 


Impreg- 
nation. 


Life  in  the 
3Iosqiiito. 


Formation  of 
Sporozoites. 


658 


INFECTION     AND     IMMUNITY. 


Parasite 

of  Q,aartaii 

Fever. 


Parasite  of 

Estivo- 

Aatnmnal 

Fever. 


'Half-Moon" 
Cells. 


eight  to  ten  days.  Such  are  the  cells  which  are 
inoculated  into  man  by  the  bite  of  the  mosquito. 
The  changes  which  they  undergo  before  they  ap- 
pear as  clear  oval  bodies  in  the  erythrocytes  are 
unknown. 

The  asexual  cycle  of  the  quartan  parasite  is 
identical  with  that  of  the  tertian,  with  the  excep- 
tion that  seventy-two  hours  are  required  for  its 
completion.  It  contains  more  pigment,  and  when 
division  takes  place  eight,  or  at  most  fourteen, 
young  parasites  are  formed,  in  contrast  to  the 
fifteen  to  twenty-five  of  the  tertian  parasites.  The 
erythrocytes  do  not  become  large  and  pale  (Euge) . 
The  sexual  cells  practically  are  indistinguishable 
from  those  of  the  tertian  parasite,  although  they 
are,  on  the  whole,  slightly  smaller.  The  sexual 
cycle  also  is  completed  only  in  the  body  of  the 
female  anopheles  mosquito,  and  is  identical  with 
that  of  the  tertian  parasite. 

The  parasite  of  sestivo-autumnal  fever  is  from 
one-half  to  two-thirds  the  size  of  the  tertian  para- 
site, a  difference  which  is  constant  in  the  various 
stages  of  development  of  the  asexual  cell.  It 
divides  eventually  into  from  eight  to  twenty-five 
young  parasites,  the  cycle  occupying  from  twenty- 
four  to  forty-eight  hours. 

Here,  as  in  quartan  fever,  the  erythrocytes  do 
not  become  swollen  and  pale,  but  even  appear 
darker  in  color,  because  of  some  shrinking  (Euge). 
The  sexual  cells  in  a^stivo-autumnal  fever  are 
characteristic.  AVhereas  they  at  first  do  not  differ 
in  shape  from  the  asexual  cells,  as  they  grow  older 
they  gradually  assume  the  shape  of  a  half  moon  in 
one  edge  of  the  erythrocyte,  reaching  a  length 
equal  to  one  and  one-half  diameters  of  the  red  cell. 


MALARIAL    PARASITE.  659 

At  this  time  a  fine  line,  drawn  across  the  concavity 
of  the  parasite  represents  the  margin  of  the  ery- 
throcyte. This  form  is  only  temporary,  however; 
they  subsequently  assume  first  a  spindle  and  then 
a  spherical  form.  As  in  the  other  parasites,  the 
male  cell  is  rather  clear  and  the  female  granular. 
When  mounted  in  a  hanging  drop  the  male  cell 
liberates  flagella,  which  penetrate  the  female  cell. 
This  does  not  occur  in  the  human  body.  In  this 
respect,  and  also  in  the  completion  of  the  sexual 
cycle  in  the  body  of  the  mosquito,  they  resemble  the 
other  two  parasites. 

The  parasites  of  tertian  and  quartan  fevers  un- 
dergo division  while  they  are  in  the  circulating 
blood,  and  when  peripheral  blood  is  examined  at  the 
end  of  the  afebrile  stage  the  young  cells  may  be 
found  extracellular.  This  is  not  the  case,  how- 
ever, in  the  sestivo-autumnal  fever.  In  this  in- 
stance, for  unknown  reasons,  the  adult  cells  with- 
draw to  the  internal  organs,  especially  the  spleen, 
bone-marrow  and  brain,  where  division  takes  place 
in  the  minute  vessels.  Hence  if  the  peripheral 
blood  is  examined  preceding  and  during  the  febrile 
stage  few  or  no  dividing  cells  or  young  parasites 
are  seen. 

Following  inoculation  by  an  infected  mosquito,  incubation 
ten  to  twelve  days  are  required  for  the  onset  of  a  ^®"®^' 
paroxysm.  In  rare  instances  the  incubation  period 
may  be  as  short  as  five  to  six  days.  This  probably 
depends  to  some  extent  on  the  number  of  organisms 
inoculated.  Malarial  infection  of  the  mosquito 
is  not  transmitted  to  the  offspring  the  latter,^ 
hence  the  bites  of  young  mosquitos  do  not  convey 

1.  This  is  questioned  by  Scbaudinn. 


660  INFECTION     AND     IMMUNITY. 

the  disease  unless  they  also  have  sucked  malarial 
blood.  The  conditions  are  different  in  relation 
to  Texas  fever,  in  which  the  infection  is  trans- 
mitted by  the  female  tick  to  her  young. 

The  aestivo-autumnal  parasite  apparently  is 
more  virulent  than  the  tertian  or  quartan.  Not 
all  cases  of  tertian  or  quartan  fever  are  equally 
severe,  and  these  variations  may  depend  on  differ- 
ences both  in  virulence  and  in  the  resistance  of  in- 
dividuals. AYhen  all  the  parasites  divide  within  a 
period  of  from  two  to  four  hours,  the  paroxysm  is 
more  intense  but  shorter  than  when  division  ex- 
tends for  from  six  to  eight  hours  (Ruge  in  rela- 
tion to  tertian  fever).  Some  of  the  severer  symp- 
toms are  due  to  the  localization  of  the  parasites 
(brain  and  intestines),  rather  than  to  special  tox- 
icity. 
Relation  of       The  mclaucmia  of  malarial  fevers  is  due  to  the 

Syiiiptons   *<* 

the  Biology  fact  that  tlic  parasitcs  absorb  the  hemoglobin  from 

Parasites^  the  erythrocytes,   transform   it  into   melanin    by 

their  metabolic  activities  and  liberate  the  melanin 

at  the  time  of  cell  division.     The  anemia  results 

from  destruction  of  the  erythrocytes. 

The  cause  of  the  fever  and  its  periodic  recur- 
rence is  more  difficult  to  explain.  As  stated  above, 
the  fever  begins  in  both  tertian  and  quartan  fevers 
at  the  time  division  forms  of  the  parasites  are  en- 
countered in  the  peripheral  blood.  Although  all 
the  parasites  do  not  divide  simultaneously,  the 
process  is  complete  within  a  period  of  four  to 
eight  hours  and  the  paroxysm  begins  early  in  this 
period.  It  is  quite  natural,  then,  to  infer  that  by 
the  division  of  the  parasite  and  the  escape  of  the 
Fever  and  J^^^S  cclls  from  the  erythrocytes,  toxic  substances 

schizoKony.  ^rc  thrown  into  the  circulation,  and  that  the  febrile 


MALARIAL     PARASITE.  661 

reaction  is  due  to  the  action  of  these  toxins. 
Methylene  blue  has  the  power  of  preventing  seg- 
mentation of  the  parasites  (Ehrlich),  and  it  has 
been  shown  that  the  paroxysm  of  fever  may  be 
averted  by  administering  methylene  blue  at  the 
proper  time.  This  corroborates  the  view  that  the 
segmentation  of  the  parasites  causes  fever  in  some 
way.  The  paroxysm  would  seem  to  represent  the 
time  required  for  the  exhaustion  of  the  toxins  set 
free  at  the  time  of  the  cell  division.- 

On  the  basis  of  the  conditions  just  cited,  the  Duration  of 
brief  duration,  sharp  limitation  and  regular  re- 
currence of  the  paroxysms  in  tertian  and  quartan 
fevers  become  intelligible.  In^a  similar  manner 
the  longer  paroxysms  and  shorter  intermissions 
which  characterize  the  typical  sestivo-autumnal  in- 
fection (i.  e.,  in  first  attacks)  are  related  to  the 
habits  of  division  of  the  corresponding  parasite. 
All  the  cells  do  not  divide  within  a  relatively  short 
period,  as  in  tertian  and  quartan  fevers,  but  the 
process  of  division  rather  stretches  out  over  from 
twenty-four  to  forty-eight  hours.  This  accounts 
for  the  longer  duration  of  the  paroxysm.  When 
the  last  cells  of  one  generation  are  dividing,  per- 
haps after  the  fever  has  gone  down,  the  first  cells 
of  the  succeeding  generation  are  well  on  toward 
maturity  and  their  division  within  a  short  time 
inaugurates  a  new  paroxysm;  the  brief  intermis- 
sion would  seem  to  be  explained  by  this  condition. 
As  the  disease  lasts  longer,  or  as  relapses  develop, 
the  periods  of  division  of  the  parasite  are  less 

2.  Roscnau,  Parker,  Francis  and  Eoyer  produced  a  typical 
paroxysm  In  a  healthy  person  by  injecting  filtered  serum 
taken  from  a  tertian  patient  during  the  chill  This  was 
intoxication,  not  infection 


/ 


Quotidian 
Fever. 


662  INFECTION     AND     IMMUNITY. 

sharply  limited  and  a  course  with  an  irregularly 
continuous  (?)  fever  may  be  established. 

Quotidian  malarial  fever  is  caused  either  by 
a  double  infection  Avith  tertian  parasites  or  a 
triple  infection  with  quartan  parasites.  In  either 
instance  a  generation  of  parasites  matures  and 
divides  every  twenty-four  hours.  The  cause  of 
the  double  or  triple  infection  is  not  known  definite- 
ly. In  some  instances  it  is  possible  that  successive 
inoculations  by  different  mosquitoes  has  occurred. 
On  the  other  hand  a  fever  which  is  primarily  ter- 
tian or  quartan  may  gradually  change  into  the 
quotidian  variety,  and  in  this  condition  it  is  pos- 
sible that  the  organisms  may  gradually  separate 
themselves  into  two  or  three  distinct  generations, 
which  reach  maturity  on  successive  days. 
Mixed       i^   other   instances   mixed   infection   with    two 

Infections. 

kinds  of  parasites  is  encountered.  This  is  usually 
aestivo-autumnal  fever  combined  either  with  ter- 
tian or  with  quartan.  Either  the  aestivo-autumnal 
may  be  primary  on  the  one  hand  or  the  tertian  or 
quartan  on  the  other.  The  clinical  course  is  com- 
plicated correspondingly.  It  is  doubtful  if  tertian 
infection  is  ever  mixed  with  quartan.  Ruge  speaks 
of  experiments  by  Dr.  Mattel  which  indicate  that 
a  mixed  infection  does  not  continue  indefinitely 
as  such.  A  patient  suffering  from  quartan  fever 
was  inoculated  with  aestivo-autumnal  blood;  in 
time  all  the  quartan  parasites  disappeared,  leav- 
ing only  the  aestivo-autumnal. 

In  malarial  cachexia  there  is  not  only  an  in- 
sufficiency of  the  blood-forming  organs,  but  other 
parenchymatous  organs  have  suffered  as  a  result 
of  prolonged  intoxication.    The  blood-forming  or- 


BLACK-WATER     FEVER 


663 


Symptoms. 


«Black-\%'ater 
Fever." 


gans  can  not  keep  pace  with  the  destruction  of  the 
erythrocytes. 

Trigeminal  and  supraorbital  neuralgias  and 
periodic  headaches  occur  sometimes  as  accompani- 
ments of  malarial  infection,  even  when  there  is 
little  or  no  fever,  and  no  parasites  may  be  dis- 
coverable in  the  blood.  That  they  are  malarial  in 
origin  is  concluded  from  the  fact  that  they  subside 
under  quinin  treatment.  In  some  forms,  and  par-  cerebral  and 
ticularly  in  gestivo-autumnal  fever,  cerebral  symp- 
toms (e.  g.,  coma)  are  marked  by  accumulations 
of  the  parasites  in  the  small  vessels  of  the  brain ; 
the  vessels  may  be  completely  occluded.  The  con- 
ditions are  similar  in  the  small  vessels  of  the  intes- 
tines in  malarial  diarrheas. 

The  so-called  "black-water  fever,"  or  hemo- 
globinuric  fever,  is  not  a  special  form  of  malaria, 
but  a  complication  which,  it  is  thought,  is  pre- 
cipitated by  insufficient  or  improper  administra- 
tion of  q-flinin  (Koch  and  others).  It  is  most  fre- 
quent in  the  tropics,  hence  in  aestivo-autumnal 
fever,  but  may  occur  in  the  tertian  and  quartan 
types.  Various  observers  have  found  that  in  from 
56  per  cent,  to  97  per  cent,  of  the  cases  quinin 
precipitated  attacks.  Stephens  and  Christopher 
were  not  able  to  exclude  quinin  as  a  factor  in  any 
of  the  cases  they  encountered.  The  essential  proc- 
ess is  a  massive  destruction  of  the  erythrocytes 
which  is  entirely  out  of  proportion  to  the  number 
of  cells  occupied  by  parasites;  few  or  no  parasites 
may  be  present.  The  amount  of  hemoglobin  thus 
liberated  is  so  great  that  it  is  excreted  largely  by 
the  kidneys;  anuria  may  result  from  occlusion  of 
the  tubules  by  pigment.  How  the  quinin,  or  the 
quinin  plus  parasites,  produce  this  extensive  hemo- 


/ 


664  INFECTION     AND     IMMUNITY. 

lysis  is  entirely  obscure;  the  effect  is  that  of  an 
intense  intoxication,  in  which  the  erythrocytes 
suffer  primarily  and  chiefly.  Craig  warns  against 
the  administration  of  one  large  dose  of  quinin  in 
the  24  hours  in  sestivo-autumnal  fever  lest  perni- 
cious symptoms  develop. 
Epidemi-  The  essential  epidemiologic  features  of  malaria 
""  *  are  the  following:  It  prevails  especially  in  tropical 
and  subtropical  zones  and  less  in  temperate  zones. 
It  is  most  abundant  in  low,  swampy  regions,  and 
in  other  places  which  afford  quiet  streams,  ponds 
or  other  standing  water.  It  is  not  directly  conta- 
gious. In  order  to  become  infected  it  is  necessary, 
customarily,  to  enter  or  be  in  close  proximity  to  a 
"malarial  district."  That  the  virus  is  not  carried 
far  from  an  infected  district  is  shown  by  the 
exemption  of  crews  of  vessels  which  lie  within  two 
or  three  miles  of  such  a  district.  Infection  has 
long  been  supposed  to  take  place  chiefly  by  night. 
The  disease  may  be  introduced  into  new  regions 
(of  suitable  climate)  by  the  importation  of  mala- 
rial subjects.  These  and  other  phenomena  of  mala- 
ria which  were  once  very  obscure  have  been  cleared 
Anopheles,  up  by  the  mosquito  theory.  There  are  many  spe- 
cies of  anopheles  and  they  are  distributed  through- 
out the  world  in  warm  and  moderate  climates. 
Anopheles  maculipennis  is  the  most  numerous  spe- 
cies, and  for  it,  as  well  as  for  Anopheles  puncti- 
pennis,  Howard  has  found  several  natural  breeding 
places  in  this  country.  It  is  probable  that  many, 
but  not  all,  species  of  anopheles  may  transmit 
malaria.  The  female  only  is  a  blood-sucker,  the 
male  living  on  vegetable  material  exclusively. 
After  the  female  has  obtained  blood  from  man  or 


TRANSMISSION,  665 

another  mammal  it  flies  to  a  suitable  pond  or  other 
collection  of  water,  where  it  deposits  its  eggs. 

"The  adult  mosquito  lays  its  eggs  on  the  surface  DeTciopment. 
of  the  water.     The  eggs  float  on  the  water  for 
some  days  (two  to  four),  after  which  they  hatch 
and  permit  the  escape  of  the  larva. 

"The  larva  is  a  free-swimming,  worm-like  ani- 
mal, which  eats  greedily  and  grows  rapidly,  cast- 
ing its  skin  several  times  in  the  process,  till  it 
reaches  its  full  development.  At  this  stage  it  sud- 
denly changes  its  form ;  casting  its  skin,  the  worm- 
like larva  assumes  a  comma  shape  and  so  becomes 
the  pupa  or  nympha. 

"During  the  pupal  period  the  insect  ceases  to 
eat;  profound  anatomical  changes  take  place  with- 
in the  pupal  skin,  whereby  the  masticatory  mouth- 
parts  of  the  larva  are  converted  into  the  suctorial 
apparatus  of  the  adult  insect  or  imago.  After  a 
certain  number  of  days  the  pupa  case  ruptures  and 
the  adult  insect  is  liberated,  furnished  with  wings 
and  legs  adapted  for  a  life  in  the  air."  (James 
andListon.) 

In  one  instance  Howard  found  the  life  cycle  of 
Anopheles  macuUpennis  to  be :  "Egg  stage,  three 
days;  larval  stage,  sixteen  days;  pupal  stage,  five 
days,  making  a  total  period  in  the  early  stages  of 
twenty-four  days."  The  rapidity  with  which  this 
process  takes  place  depends  largely  on  the  tem- 
perature; it  is  more  rapid  in  the  hot  weather  of 
July  and  August  than  in  the  cold  days  of  May. 
Anopheles  usually  does  not  lay  its  eggs  in  tin  cans 
or  barrels  of  water,  but  preferably  in  more  open 
or  cleaner  water.  Excavations  which  have  become 
filled  with  water  are  favorable  places,  as  are  also 
collections  of  water  from  springs. 


666  INFECTION     AND     IMMUNITY. 

Misration  of       The   anopheles   leads   an   adult   life   for   many 
Anopheles,  j^^j^^j^g   ^^^^  ^^^  g^gj^  hibernate  under  suitable 

conditions  either  in  the  adult  or  larval  form.  It 
is  generally  stated  that  the  insects  do  not  fly  more 
than  half  a  mile  from  their  breeding  and  feeding 
grounds.  Their  dispersal  certainly  extends  beyond 
these  limits,  however.  James  and  Liston  enumer- 
ate the  following  methods  of  dispersal:  (1)  by 
direct  flight  over  considerable  distances;  (2)  by 
the  eggs  and  larvae  being  carried  in  streams  and 
canals;  (3)  by  a  multiplication  of  successive  short 
flights  by  adults;  (4)  in  conveyances. 

Anopheles  avoids  high  winds  and  rains,  seeks 
shelter  on  excessively  hot  days  and  feeds  and  bites 
chiefly  or  only  after  sunset  and  before  sunrise. 
The  latter  habit  confirms  the  old  belief  that  ma- 
larial infection  occurs  chiefly  at  night. 

For  further  details  as  to  the  morphology  and 
habits  of  the  insect  in  its  different  stages,  and  for 
differentiation  of  the  different  genera  and  spe- 
cies, one  should  consult  a  textbook  of  entomology, 
or,  for  example,  the  book  on  "Mosquitos,"  by  How- 
ard (McClure,  Phillips  &  Co.,  New  York). 
Proi>hyiaxis.  Individual  prophylaxis  may  be  accomplished  and 
maintained  by  taking  small  daily  doses  of  quinin, 
or  larger  doses  (1  gram)  every  few  days.  One  who 
has  had  malaria  may  likewise  prevent  recurrence 
by  suitable  quinin  treatment.  Quinin  has  the 
power  of  preventing  division  of  the  parasites,  and 
therefore,  the  power  of  preventing  the  paroxysms. 
"K.  Koch's  procedure  consists  in  this,  that  one 
takes  a  gram  of  quinin  every  tenth  and  eleventh 
day,  and  if  fever  still  develops,  every  ninth  and 
tenth  day."     (Ruge.) 


PROPHYLAXIS.  G67 

Other  points  in  individual  prophylaxis  are,  first, 
the  application  of  ethereal  oils  (clove  oil,  oil  of 
pennyroyal)  to  the  exposed  skin,  and,  second,  the 
use  of  mosquito  netting. 

The  important  practices  for  general  prophylaxis  ^^asures 
are  the  following:  1.  The  draining  of  swampy 
places  and  of  pools  of  water  where  anopheles  may 
deposit  its  eggs.  This  in  many  instances  manifest- 
ly can  not  be  accomplished.  2.  Covering  pools  of 
water  with  petroleum.  This  is  to  a  degree  success- 
ful. Every  square  meter  requires  0.5  liter  of  pe- 
troleum (Kerschbaumer),  and  the  oil  must  be 
added  fresh  every  seven  or  eight  days.  The  layer 
of  oil  excludes  the  air  from  the  larval  mosquitoes 
and  they  drown.  If  fresh  oil  is  not  added  occa- 
sionally new  eggs  may  hatch;  3.  Koch^s  method  of 
extermination  of  malaria.  This  consists  of  the 
searching  out  of  all  cases  of  malaria  and  the  de- 
struction of  the  parasites  by  appropriate  quinin 
treatment.  Koch  practiced  this  method  in  an  in- 
fected locality  of  New  Guinea  and  in  a  relatively 
short  time  freed  it  of  malaria.  If  all  the  plasmodia 
in  a  community  are  destroyed  the  disease  can  not 
again  become  endemic  unless  it  is  introduced  from 
without  or  unless  infected  mosquitoes  are  imported. 
Manifestly  this  method  must  be  practiced  on  an  ex- 
tensive scale  in  order  to  render  it  permanently 
successful.  It  seems  to  have  been  demonstrated, 
however,  that  the  number  of  cases  in  any  given 
locality  may  be  materially  decreased  by  pursu- 
ing it. 

So  far  as  is  known,  susceptibility  to  malaria  is   immunitF. 
universal.     The  belief   is   very  general  that  one 
attack  of  malaria  not  only  does  not  protect  against 
reinfection,  but  even  predisposes  to  it.    Two  facts. 


668  INFECTION     AND     IMMUNITY. 

however,  show  that  acquired  immunity  (relative 
or  absolute)  is  possible.  First,  in  certain  regions 
of  Africa  where  malaria  is  endemic  the  adult  na- 
tives rarely  suffer  from  the  disease,  and  then  only 
from  light  attacks,  whereas  European  visitors  con- 
tract the  disease  in  severe  form.  The  cause  of  this 
immunity  was  explained  by  Koch.  "Koch  found 
that  the  native  adults  of  malarial  countries  were 
free  from  malaria,  but  that  the  children  suffered 
almost  universally  from  malarial  diseases.  If 
they  recovered  from  the  original  infection  they 
became  immunized  in  time  through  continued  new 
attacks  or  relapses,  the  number  of  malarial  chil- 
dren gradually  decreased  with  their  age,  and  in  the 
v^icinity  of  the  tenth  year  the  only  evidence,  in 
general,  of  a  previous  infection  was  an  enlarged 
spleen,  and  even  this  disappeared  during  puberty, 
so  that  the  adult  natives  finally  appeared  as 
healthy  and  malaria-immune  persons."  (Ruge.) 
The  objection  raised  by  many  that  such  immunity 
is  not  observed  in  Italy  and  other  civilized  coun- 
tries where  malaria  is  endemic,  is  met  by  the  fact 
that  the  disease  in  these  countries  is  not  permitted 
to  run  an  uninterrupted  course.  Treatment  with 
quinin  is  instituted  and  the  immunizing  process 
is  thereby  broken  off.  Koch  also  established  the 
fact  that  immunity  against  one  type  of  parasite  is 
not  efficient  against  other  types. 

Second,  in  civilized  countries  it  has  often  been 
noted  that  subsequent  attacks  are  of  a  milder  char- 
acter than  the  primary;  the  disease  may  in  time 
"wear  itself  out,"  even  without  quinin  treatment, 
Ruge  gives  as  an  accompaniment  of  this  immuniz- 
ing process  the  occurrence  of  the  sexual  cells  in 
large  numbers,  even  up  to  50  per  cent,  of  the  total 


MALARIA     OF    BIRDS. 


669 


number  of  parasites  (tertian  fever).  In  such 
cases  large  numbers  of  the  parasites  die  before 
they  reach  maturity,  their  death  being  indicated 
by  shrinking  and  clouding  of  the  cells  and  altera- 
tions in  or  disappearance  of  the  chromatin.  It  is 
somewhat  characteristic  of  quartan  fever,  and  still 
more  so  of  oBstivo-autumnal,  that  the  sexual  cells 
are  much  more  numerous  in  recurrences  than  in 
primary  attacks.  One  may  be  able  to  differentiate 
a  relapse  from  the  primary  attack  by  the  number 
of  sexual  cells  encountered  (Ruge). 

Nothing  in  the  way  of  serotherapy  has  been 
accomplished,  and  it  is  doubtful  if  any  serum 
could  equal  quinin  in  efficacy. 


MALARIA    OF    BIRDS. 

Diseases  considered  to  be  true  malaria  also  occur  in 
birds. 

One  of  these  diseases  is  caused  by  a  proteosome  {Pro- 
teosoma  Lahh6,  Gystosporon  danielewsky,  Hemameha  re- 
Ucta).  Sparrows,  hawks,  buzzards,  crows  and  pigeons 
are  affected.  Like  the  malarial  parasites  in  man,  the 
parasite  enters  the  erythrocytes  and  has  both  a  sexual 
and  an  asexual  cycle  of  development,  the  latter  taking 
place  in  the  infected  animal,  the  former  in  the  stomach 
of  the  common  mosquito  {Gulex  pipiens).  Hence  in  its 
development  proteosoma  is  perfectly  analogous  to 
Plasmodium.  This  disease  is  transmissible  from  bird  to 
bird  by  the  inoculation  of  infected  blood. 

Halteridium  is  still  another  hemosporidium  which  in- 
fects birds.  It  was  in  the  study  of  this  organism  that 
MacCallum  first  saw  the  phenomenon  of  impregnation. 
All  the  cells  seen  in  the  blood  appear  to  be  divisible  into 
male  and  female,  and  although  MacCallum  had  seen  im- 
pregnation in  microscopic  preparations  the  life  cycle  for 
a  long  time  was  obscure.  Recently  Schaudinn  has  found 
that  the  sexual  cycle  is  completed  in  Gulex  pipiens.  He 
considers  the  organism  to  be  a  trypanosome.  "I  have 
been  able  to  prove  that  the  halteridium  is  the  sexual 


Proteosome. 


Halteridiain. 


670  INFECTION     AND     IMMUNITY. 

stage  of  a  trj-panosome  which  multiplies  in  the  commoE 
mosquito — Gulex  pipiens — and  after  a  complicated  mi- 
gration through  the  body  of  the  mosquito  is  again  in- 
troduced by  its  bite  into  the  blood  of  the  owl,  where, 
after  a  period  of  sexual  multiplication,  it  is  transformed 
into  the  well-known  male  and  female  halteridium." 

IT.     TRYPANOSOMIASIS. 

GennN  Griibj  Created  the  genus  Trypanosoma  in  1843, 
""^Homa"  when  he  gave  the  name  of  Trypanosoma  sanguinis 
to  a  flagellate  protozoon  which  he  found  in  the 
blood  of  frogs.  Since  that  time  similar  organisms 
have  been  found  in  the  bloods  of  many  animals  and 
the  genus  Trypanosoma  has  growm  to  considerable 
dimensions.  It  is  not  improbable,  however,  that 
a  number  which  now  bear  independent  names  will 
be  shown  to  be  identical.  This  suggests  itself  par- 
ticularly in  relation  to  trypanosomiasis  in  horses, 
in  which  the  infections  are  known  under  four  sep- 
arate names  in  different  countries,  and  the  para- 
sites are  given  separate  specific  names.  The  study 
of  these  infections  is  so  young  and  has  been  prose- 
cuted in  such  widely  separated  countries  that  the 
existing  chaos  is  quite  natural  and  can  be  adjusted 
only  as  time  and  circumstances  permit  of  close 
comparative  study.  Until  such  a  time  the  prevail- 
ing views  as  to  independence  of  species  and  of  in- 
fections must  be  recognized. 

Trypanosomas  vary  a  great  deal  in  size  and  mor- 
phology. Eoughly,  they  are  from  one  to  five  mi- 
crons thick  and  from  fifteen  to  forty-five  microns 
long,  including  the  flagellum.  All  species  possess 
active  eel-like  movements,  some  traveling  rapidly, 
others  slowly.  A  long,  actively-motile  flagellum 
projects  from  the  anterior  end,  and  where  it  joins 


TRYPANOSOMIASIS.  671 

the  cell  body  is  continuous  with  an  "undulating 
membrane/'  which  extends  along  a  border  of  the 
organism  to  a  point  near  the  centrosome  or  mi- 
cronucleus  in  the  posterior  portion  of  the  cell. 
The  centrosome  is  sometimes  spoken  of  as  anala- 
gous  to  the  "eye  spot''  of  some  other  protozoa.  The 
undulatino-  membrane  is  more  or  less  wavy  or 
folded  and  its  breadth  varies.  The  centrosome  pre- 
sumably has  a  close  relationship  to  the  undulating 
membrane,  and,  through  the  latter,  with  the  ilagel- 
lum.  The  nucleus  is  in  the  anterior  portion  of 
the  parasite.  In  relation  to  some  species  a  con- 
tractile vacuole  is  spoken  of.  An  endoplasm  and 
an  ectoplasm  may  be  differentiated. 

Division  of  trypanosomes  is  nearly  always  longi- 
tudinal, rarely  transverse.  In  the  process  of  longi- 
tudinal fission  the  order  of  division  of  the  differ- 
ent parts  of  the  cell  is  as  follows :  1,  Centrosome ; 
2,  flagellum;  3,  nucleus  and  protoplasm  (Laveran 
and  Mesnil).  After  division  has  occurred  the  two 
cells  may  remain  attached  at  their  posterior  ends 
for  some  time.  By  a  repeated  division  of  young 
cells,  the  posterior  ends  remaining  attached,  ros- 
ettes are  said  to  be  formed.  Others  consider  ros- 
ette formation  as  a  phenomenon  of  agglutination. 
Possibly  both  phenomena  occur. 

Koch  and  others  have  described  sexual  repro- 
duction in  the  tsetse-fly. 

Koch  divides  the  trypanosomes  into  two  classes  classification. 
as  to  constancy  in  respect  to:     (1)  morphology; 
(2)   virulence;    (3)   host.     This    classification    is 
best  represented  by  the  accompanying  table  from 
Xocht  and  Maver. 


fa 


CO 

o  a) 
aiii, 


a 


Sat*  o  a 
e 


e     S 


^00.5 

I'd  . 


be 

D 
O 

.£3 


a  05  "o  'o 

-pi 
1^=1 


o-S* 
C3  a. 


3 

o 


-.5  fl  t- 

3-^ 


;fk 


e3  03  o 

3  o  s-c 


a 

.a 

3 
o 


o3  '^ 


a 

bO 


«} 


W   M          M 

CO 

^  bCS  rt 

r/r>..r 

Animal 

as 

Host 

S 
1 

to" 

0 
0 

Horses,   co 

camels,   do 

less  ofte 

other  anim 

Most 
mammal 
especiall 
domestic 

Oi 
V 
CO 

0 

CO 
CO 

0 

(0 
0) 

ki 

0 

Cause 
of 

Disease 

Usually 
causes  no 
symptoms 
of  disease. 

13 
0 

to 

M 

3 

CO 

3 

eg       aj 
3       w 

•S 

3 
0 

Q 

m  72 
hi 

6*aj 
a  CO 

aq 
55  w 

Trypano- 
somiasis 
of  horses. 

>> 

-d 
« 

CO 

i?2 

r-loo 

0 

0 

TJI 

SS«^ 

0 

05 

»-i 

CO 

0 

N      'O 

0 

0 
r-l 

CO 

00 
1-1 

05 
CO 

0 

05 

rH 

05 
rH 

3^ 
0 

.2 
.3 

co" 

3 

> 

Rouge  t, 
Schnelde 
Buffard, 

73 

eJ 

a 

0 

3 

Q 

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OS  05 

3 

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a 

ej 

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leileri 
B,  Bruce, 
32) 

CCQO 
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Cr-( 

rucei 
er  and 
d,  1899) 

is- 

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S    - 

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1^ 

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205 

S  3 

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orphon 
and  Todd, 
52) 

0 

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a  CO 

On: 
So! 

.1    » 

^9^ 

0 
0 

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b.t4 

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s;w 

t^3 

Q 

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•4SOH 

oBo 

puB  aDua^n 

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ivSoioqdJOK 

•;soH 

puB  aoaainjjA 

'ifSoioqdJOK  0^ 

SB  ;aB;suooni     | 

>  0    ; 

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J 

II 

dnoJO 

<^2 

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dnojo 

TRYPANOSOMIASIS. 


673 


TRYPANOSOMIASIS    IN   MAN. 

Nepveu   in   1898   first   found  trypanosomes   in   Trypanoso- 

^  .  .  matic 

the  blood  of  man  in  Algiers  in  eight  cases.  His  ob-  Fever. 
servations  were  passed  over  temporarily.  The  para- 
site bears  his  name  {T.  nepveui).  Again  in  1901 
Forde  discovered  similar  parasites  in  Western 
Africa  (Gambia),  and  since  tJiat  time  a  numbej* 
of  cases  of  ^'Gambian  fever"  or  tr3^panosomatic 
fever  in  man  have  been  imported.  In  this  in- 
stance the  parasite  was  called  T.  gamhicnsc  by  But- 
ton and  T.  Iwminis  by  Manson.  The  disease  is 
said  to  follow  the  bite  of  a  tsetse-fly  (Glossina 
palpalis),  at  least  in  some  instances.  The  tissues 
around  the  bite  become  inflamed  and  in  from  a 
few  days  to  two  weeks  recurring  attacks  of  fever 
set  in,  and  a  patchy  and  ringed  erythematous  erup- 
tion appears  on  the  skin.  Forde  gives  as  the 
chief  clinical  findings  in  his  case:  (1)  the  "irregular 
intermittent  temperature;  (2)  the  edematous  con- 
dition of  the  face  and  lower  extremities;  (3)  the 
rapid  and  variable  pulse  and  respiration,  unac- 
companied by  any  evident  cause;  (4)  loss  of 
weight,  with  marked  debility,  wasting  and  lassi- 
tude; (5)  the  persistence  of  these  symptoms  and 
their  resistance  to  treatment.  The  parasites  are 
most  numerous  in  the  blood  at  the  time  of  the 
febrile  attacks.     Eecovery  has  not  been  reported. 

Sleeping  sickness  has  been  endemic  in  certain  sleeping 
districts  of  Africa  for  a  long  time,  and,  although 
confined  to  a  very  limited  district  at  one  time,  it  ap- 
pears now  to  have  extended  to  distant  parts.  Speak- 
ing of  trypanosomatic  fever  and  sleeping  sickness 
collectively,  Ruata  says  that  while  originally  con- 
fined to  a  small  district  in  Western  Africa  between 


Sickness. 


674 


INFECTION     AND     IMMUNITY. 


Octtnrreuce. 


Trypano- 
somes  in 
Sleeping^ 
Sickness. 


the  latitudes  15'  North  and  15'  South,  it  is  now 
found  one  thousand  miles  up  the  Congo  (Bangola, 
Stanley  Falls)  and  in  East-central  Africa  on  the 
shores  of  the  Victoria  Nyanza  Lake.  "Now  it  ex- 
tends from  the  mouth  of  the  Katonga  Kiver 
through  Uganda  (1901,  Cook),  Kome  Island, 
Busaga,  Buvuma,  Kavirondo,  Kisumu,  Lumbwa, 
Homa,  Kasagunga,  Lusinga  Island,  the  eastern 
sliores  of  the  lake,  joining  the  south  of  the  bound- 
ary river  Gori  in  the  Udemi  district  of  the  Sultina 
of  Obo"  (Euata). 

Its  extension  supposedly  has  been  facilitated  by 
rapid  transit.  "The  disease  is  most  prevalent 
amongst  the  inhabitants  of  low-lying  shambas  (ba- 
nana and  potato  plantations)  in  places  along  the 
shores  of  the  Victoria  Nyanza,  or  in  wooded  dis- 
tricts not  far  from  the  water"  (Christy).  Those 
living  on  high  ground  are  much  less  infected  than 
those  living  in  the  low  moist  places  near  water.  A 
great  deal  of  stress  is  laid  on  its  close  association 
with  inland  bodies  of  water. 

It  apparently  has  no  relation  to  sex,  age,  sea- 
sons, food  or  drinking  water,  and  is  related  to  oc- 
cupation only  in  so  far  as  the  occupation  carries 
one  into  the  low  places  mentioned. 

At  one  time  (1891)  Manson  advanced  the  idea 
that  sleeping  sickness  is  caused  by  the  minute 
Filaria  perstans.  It  has  since  developed  that  this 
parasite  occurs  in  70  per  cent,  of  the  natives  in 
certain  districts,  and  that  sleeping  sickness  may 
occur  in  areas  in  which  Filaria  perstans  does  not 
exist;  Manson  has  abandoned  this  view.  A  num- 
ber of  investigators  also  found  cocci  in  the  cerebro- 
spinal fluid,  but  this  occurred  very  rarely  during 
life  and  at  a  late  stage  of  the  disease ;  such  organ- 


TRANSMISSION.  675 

isms-  are  probably  secondary  or  agonal  invasions 
in  spite  of  their  rather  frequent  occurrence.  Fur- 
ther investigations  by  Castellani  disclosed  the  pres- 
ence of  a  trypanosome  (T,  castellani)  in  the  cere- 
brospinal fluid  of  a  large  percentage  of  the  cases, 
and  a  little  later  Bruce  found  this  organism  in  all 
the  cases  he  had  examined.  This  observation  has 
been  confirmed  so  many  times  that  the  trypan- 
osome is  now  generally  considered  as  the  cause  of 
the  disease. 

Sleeping  sickness  is  not  contagious  in  the  or-  tsetse 
dinary  sense,  and  Bruce  furnishes  very  strong 
evidence  that  it  is  transmitted  by  the  bite  of 
a  tsetse-fly  {Glossina  palpalis).  The  distribu- 
tion of  the  disease  corresponds  to  the  habitat  of 
this  fly,  and  Bruce  transferred  the  infection  to 
monkeys  by  means  of  flies  which  had  bitten  those 
suffering  from  sleeping  sickness.  Gray  and  Tul- 
lach  have  demonstrated  the  presence  of  trypano- 
somes  in  the  alimentary  canal  of  tsetse  flies  which 
were  allowed  to  feed  on  the  blood  of  patients  with 
sleeping  sickness. 

A  pronounced  lethargy  or  somnolence  is  the  symptomi*. 
most  striking  clinical  feature  of  the  disease.  "The 
appearance  of  the  somnolent  condition  is  preceded, 
often  for  a  long  time,  by  prodromal  signs,  which 
are  so  characteristic  that  the  patient's  neighbors 
cannot  possibly  be  deceived  as  to  the  fate  that 
awaits  him.  The  victim  complains  of  weakness, 
langour,  dejection,  disinclination  for  work,  head- 
aches, particularly  localized  over  the  occiput,  a 
sensation  of  weight  in  the  head  and  giddiness. 
His  eyelids  tend  continually  to  close  and  he  has  a 
tendency  to  go  to  rest  at  unusual  hours  of  the  day; 
for  this  purpose  he  seeks  out  lonely  quiet  spots> 


67G  INFECTION     AND     IMMUNITY. 

where  he  spends  a  long  time  in  dozing"  (Scheube). 
For  some  time  he  is  able  to  resist  the  somnolence, 
and  when  aroused  gives  intelligent  answers.  He 
.  eventually  acquires  an  unsteady  gait  and  walks 
about  like  a  drunken  man.  The  temperature  of 
the  body  appears  to  be  lowered,  although  irregular 
attacks  of  fever  occur.  The  somnolence  gradually 
becomes  more  intense,  the  patient  grows  very  weak, 
the  pulse  small  and  thready,  respiration  difficult, 
the  edema  seen  in  trypanosomatic  fever  is  rather 
constant,  incontinence  of  the  urine  and  feces  may 
develop;  the  patient  commonly  dies  after  passing 
into  a  state  of  deep  stupor.  Convulsions  and  pa- 
ralyses are  noted;  the  mind  usually  is  clear  when 
the  patient  is  conscious,  although  maniacal  at- 
tacks and  delusions  are  occasionally  noted.  The 
cervical  and  superficial  lymphatics  are  frequently 
but  not  constantly  enlarged.  A  papulo-vesicular 
eruption  is  quite  characteristic  and  persistent  and 
the  skin  becomes  very  dry.  The  incubation  period 
varies  from  six  to  eighteen  months,  and  the  som- 
nolent state  from  three  to  twelve  months.  Recov- 
ery rarely  occurs. 

Meninso-       The  csscntial   anatomic  change  is  meningo-en- 
E:ncepiiaiiti8.  cephalitis,   the   soft   membranes   being   thickened, 
containing  a  milky  fluid  and  the  vessels  of  the  pia 
and  brain  being  surrounded  by  an  extensive  infil- 
tration of  mononuclear  leucocytes. 
Identity  of       The  discovcry  of  trypanosomes  in  sleeping  sick- 

'^^Homa'tic  ^^ss    suggcstcd    that    trypanosomatic    fever    may 
'^Vieepine  really  represent  the  long  prodromal  stage  of  sleep- 

sicknens.  i^g  sickucss.  This  vicw  has  been  greatly  strength- 
ened by  a  case  reported  by  Manson  in  which  a 
typical  case  of  trypanosomatic  fever  was  seen  to 
pass  into  typical  and  fatal  sleeping  sickness.    The 


SLEEPING    SICKNESS.  677 

wife  of  a  missionary  in  upper  Congo  was  bitten 
by  a  tsetse-fly,  and  following  an  inflammatory  re- 
action at  the  seat  of  the  bite,  she  developed  and  ran 
a  long  course  of  trypanosomatic  fever.  After  from  a 
year  and  a  half  to  two  years  of  remittent  attacks 
of  fever,  the  organisms  being  found  in  the  blood 
repeatedl}',  she  grew  weaker,  became  somnolent 
and  died  in  a  comatose  condition.  The  anatomic 
changes 'at  autopsy  were  t^^pical  of  sleeping  sick- 
ness. Some  who  are  not  quite  willing  to  accept  the 
unity  of  the  two  diseases  suggest  that  the  sleeping 
siclvness  may  have  been  superimposed  on  trypano- 
somatic fever. 

Assuming  that  the  two  conditions  represent  dif- 
ferent stages  of  the  same  disease,  we  would  have 
to  recognize  trypanosomatic  fever  as  the  first  stage 
and  the  lethargy  of  sleeping  siclaiess  as  the  second. 
If  this  proves  to  be  correct  the  name  of  T.  nepveui 
should  be  retained  for  the  organism  and  the  other 
names  dropped  {T.  gamhiensc,  T.  liominis,  T. 
castellani) . 

It  is  believed  that  T.  castellani  is  a  distinct  Tiie 
species  of  trypanosome.  It  is  hardly  possible  to  as- 
sociate it  with  nagana,  since  sleeping  sickness  and 
nagana  do  not  coincide  in  their  distribution,  and, 
moreover,  the  morphology  and  pathogenicity  of 
T.  castellani  differ  from  that  of  T.  brucei.  The 
former  is  not  infectious  for  the  "donkey,  ox, 
guinea-pig,  dog,  pup,  goat  and  sheep"  (Euata). 
T.  castellani  is  from  IS  to  25  microns  long  and 
from  2  to  2.5  broad.  Its  morphology  in  general 
is  like  that  of  other  trypanosomes,  although  there 
are  suflicient  differences  to  establish  its  independ- 
ence. Its  motility  is  rather  slow^  and  in  contrast 
to  other  trypanosomes  it  moves  in  the  direction  of 


678  INFECTION     AND     IMMUNITY. 

its  non-flagellated  end.  The  failure  to  find  any 
distinctive  difl:erence  between  this  organism  and 
T.  neprevi  {T.  gamhiense)  is  an  additional  point 
in  favor  of  the  unity  of  trypanosomatic  fever  and 
sleeping  sickness. 

TRYPANOSOMIASIS    IN   ANIMALS. 
On  account  of  the  prevailing  general  interest  in  the 
subject,   the  more   important  trypanosomatic   infections 
in    animals    and    the    corresponding    parasites    v/ill    be 
sketched  briefly. 
General       Musgrave  and   Clegg  speak  of  certain  general   symp- 
Symptomat-    toms  which  are  common  to  surra,  nagana,  mal  de  caderas 
olosy.    j^j^(j  dourine,  as   follows:     "After  an   incubation  period, 
which  varies  in  the  same  class  of  animals  and  in  those  of 
different  species  as  well  as  with  the  conditions  of  infec- 
tion,   and    during   which   the    animal    remains    perfectly 
well,  the  first  sjTiiptom  to  be  noticed  is  a  rise  of  tem- 
perature, and  for  some  days  a  remittent  or  intermittent 
fever  may  be  the  only  evidence  of  illness.     Later,    the 
animal  becomes  somewhat  stupid;   watery  catarrhal  dis- 
charges from  the  nose  and  eyes  appear;  the  hair  becomes 
somewhat   roughened  and  falls  out  in  places.     Finally, 
the  catarrhal  discharges  become  more   profuse  and  the 
secretion  more   tenacious   and   even  purulent;    edema  of 
the  genitals  and  dependant  parts  appears;   a  staggering 
gait,  particularly  of  the  hind  parts,  comes  on  and  is  fol- 
lowed by  death." 
Infections-        The   incubation   period   varies   from   a   few   to   several 

"«i'''  **i^    days.     Pronounced  anemia  develops,  the  method  of  de- 
Blood.  "^  ,     .  ,  T  ^      !_' 

struction  of  the  erythrocytes  being  unknown.  Lymphatic 
enlargement  is  the  rule,  and  during  the  incubation  period 
the  parasites  probably  undergo  great  proliferation  in  the 
l.\nTiph  glands.  It  is  somewhat  characteristic  that  mas- 
sive invasion  of  the  blood  streams  occurs  periodically. 
With  a  paroxysm  of  fever  their  numbers  increase  in  the 
blood,  and  during  the  intermission  they  decrease  and 
may  be  so  few  as  not  to  be  found  microscopically.  Even 
when  few  or  no  parasites  are  found  in  the  circulation, 
however,  the  blood  usually  is  infectious  for  other  ani- 
mals.    During  the  intermissions  it  is  possible  that  they 


CULTIVATION    OF    TRYPANOSOMES.         679 

are  largely  within  the  lymph  glands  or  other  internal 
organs.  The  cause  of  these  variations  is  not  known,  and 
it  can  not  be  said  now  that  they  are  related  to  cycles  of 
development  like  those  of  the  malarial  parasites.  Voges 
suggests  that  they  may  represent  the  establishment  of 
successive  periods  of  temporary  immunity  {mal  de 
caderas).  These  are  only  general  features,  and  varia- 
tions occur  in  infections  in  different  animals  and  by  dif- 
ferent parasites. 

Trypanosoma  lewisi,  recognized  in  the  blood  of  the  rat  Tryi)anoso- 
by  Lewis  in  1879,  and  given  its  present  name  by  Kent  Rats.*"  *** 
in  1882,  infects  wild  rats  throughout  the  world,  and  in 
some  localities  a  very  high  percentage  of  the  animals  are 
infected.  The  parasite  is  readily  found  in  the  peripheral 
blood  (as  from  the  tail),  where  a  large  number  may  be 
present  in  a  single  field  of  the  microscope;  sometimes, 
however,  prolonged  search  is  necessary  for  their  discov- 
ery. Its  dimensions  vary:  from  1.4  to  3  microns  in  diam- 
eter, and  from  10  to  25  microns  in  length,  according 
to  different  observers.  It  is  of  lancet-form,  pos- 
sesses a  finely  granular  endoplasm  and  a  clear 
ectoplasm,  and  from  the  latter  spring  the  fiagel- 
lum  and  the  undulating  membrane.  "The  for- 
mer (flagellum)  is  about  as  long  as  the  body  itself; 
it  originates  at  the  posterior  end  of  the  animal  in  a 
granule-like  structure,  called  the  flagellar  root,  extends 
forward  as  a  marginal  thickening  of  the  undulating 
membrane  and  becomes  free  only  at  the  anterior  end  of 
the  animal  from  which  it  extends  into  the  surrounding 
endomedium  as  a  flagellum"  (Doflein).  At  its  posterior 
extremity  the  parasite  ends  in  a  sharp  point.  In  its  an- 
terior portion  it  contains  a  strongly  staining  nucleus;  a 
contractile  vacuole  is  not  described.  Its  motility  is,  per- 
haps, more  active  than  that  of  any  other  trypanosome, 
and  in  a  fresh  mount  of  rat's  blood  it  may  move  across 
the  field  so  rapidly  as  to  be  followed  with  difficulty. 

Division  takes  place  by  longitudinal  fission  (rarely 
transverse),  and  by  repeated  division  rosettes  are 
formed. 

Novy  and  McNeal  succeeded  in  cultivating  this  organ-    Cnltlvatios 
ism  artificially  on  a  medium  consisting  of  rabbit's  blood, 
2  parts,  agar,   1   part.     The  growth  occurs   in  the  con- 


680  IXFECTIOy     AiYD     IMMU^NITY. 

densation  fluid,  and  the  organisms  were  carried  through 
many  generations.  In  cultures  they  vary  greatly  in  size 
(from  1  to  60  microns  in  length).  "The  existence  of  the 
small  forms  accounts  for  the  fact  that  we  have  repeat- 
edly been  able  to  infect  rats  with  Berkefeld  filtrates  of 
such  cultures."  It  is  remarkable  that  so  many  of  the 
rats  which  harbor  the  parasites  appear  to  be  perfectly 
healthy.  However,  the  animals  not  infrequently  die 
from  the  infection,  and  in  some  instances  fairly  severe 
epidemics  have  been  noted.  The  infection  is  found  also 
in  the  hamster,  a  European  rodent,  and  in  white  rats. 
White  mice  are  susceptible  to  inoculation  (Doflein). 
>'agann.  Trypanosoma  brucei,  found  by  Bruce  in  1894  in  the 
blood  of  animals  suffering  from  nagana  or  the  tsetse-fly 
disease  in  Zululand  is  somewhat  different  morphologi- 
cally from  T.  lewisi,  being  more  worm-like  in  form,  hav- 
ing a  blunt  posterior  extremity,  less  motility  and  greater 
pathogenicity.  "The  undulating  membrane  is  broader 
and  more  plicate,  the  protoplasm  colors  more  easily  and 
more  deeply"  than  in  T.  lewisi.  Its  length  is  said  to 
vary,  depending  on  the  animal  which  harbors  it,  being 
largest  in  the  rat  and  shorter  and  thicker  in  the  dog. 
Its  dimensions  as  given  by  Laveran  and  Mesnil  are  1  to 
1.5  by  26  to  27  microns.  Its  structure  is  similar  to  that 
of  T.  lewisi,  containing  a  nucleus  near  the  middle  of  the 
body  and  a  deeply  staining  centrosome  in  the  posterior 
portion  in  or  near  which  the  flagellum  has  its  origin. 
A  contractile  vacuole  lies  anterior  to  the  centrosome. 

Natural  infection  (nagana)  with  this  organism  occurs 
in  horses,  cattle,  mules,  and  also  in  some  wild  animals, 
as  camels,  buffaloes  and  hyenas.  It  is,  however,  a  tropi- 
cal disease,  occurring  chiefly  in  various  parts  of  South 
Africa.  Nearly  all  animals  are  susceptible  to  artifi- 
cial infection  by  the  injection  of  diseased  blood. 
TsetNc  "^^^  distribution  of  nagana  corresponds  with  the  dis- 
F^Jy-  tribution  of  the  tsetse-fiy,  and  Bruce  discovered  that  this 
fly,  after  feeding  on  the  blood  of  an  infected  animal, 
transfers  the  disease  to  others  by  biting.  Horses,  asses, 
cattle  and  hogs  were  infected  artificially  in  this  way,  but 
man  appears  not  to  be  susceptible.  It  is  assumed,  but 
perhaps  not  definitely  proved,  that  no  other  fly  or  insect 
transmits  the  disease.     Immediately  after  it  has  fed  on 


CULTIVATION    OF    TRYPANOf^OMES,         681 

infected  blood  it  is  capable  of  transferring  the  disease  j 
hence,  further  development  of  the  parasite  in  the  tsetse- 
fly  is  not  essential  for  its  continued  infectiousness,  and, 
indeed,  it  is  not  certain  that  any  further  development 
occurs. 

Nagana  presents  a  remittent  or  intermittent  type  of 
fever,  catarrhal  secretion  from  the  nose  and  eyes,  sub- 
cutaneous edema,  particularly  of  the  abdominal  region, 
prepuce  and  posterior  extremities,  roughening  and  shed- 
ding of  the  hair,  marked  emaciation,  weakness  and  ane- 
mia develop,  and  the  animal  dies  in  a  state  of  exhaus- 
tion. The  spleen  is  greatly  swollen,  the  red  corpuscles 
are  diminished  in  number,  and  the  urine  may  be  blood 
stained.  The  parasites  are  found  in  enormous  numbers 
in  the  blood. 

The  disease  is  almost  invariably  fatal.  It  may  last 
for  weeks  or  months  in  horses,  and  even  much  longer  in 
cattle.      It    occurs    not    infrequently    in    epidemic    form,  « 

wiping  out  the  horses  and  cattle  of  infected  regions.  In 
wild  animals  it  is  suggested  that  the  disease  may  be 
more  chronic,  and  the  shifting  of  such  animals  may 
serve  to  introduce  the  infection  to  new  regions,  but  only 
to  such  regions  as  harbor  the  tsetse-fly. 

Novy  and  McNeal  cultivate  T.  hrucei  on  a  medium  Cultivation. 
similar  to  that  used  for  T.  lewisi.  The  former  is  more 
exacting  in  its  conditions  for  growth,  preferring  a  me- 
dium containing  blood  and  agar  in  a  ratio  of  two  to  one 
or  three  to  one.  Cultures  were  kept  alive  for  at  least 
one  hundred  days  through  eight  generations,  although 
virulence  was  soon  lost. 

Trypanosoma  evansi  is  the  name  given  by  Steele  to  a  ji-^j^.^.^^ 
parasite  discovered  by  Evans  (1880),  in  India,  in  the 
blood  of  horses  suffering  from  surra.  It  has  the  same 
general  morphologic  features  as  T.  hrucei,  with  dimen- 
sions from  1  to  3.5  or  4  microns  by  20  to  35  microns,  in- 
cluding the  flagellum  (Musgrave  and  Clegg).  It  con- 
tains a  nucleus  and  possibly  a  contractile  vacuole.  The 
whole  posterior  extremity  is  contractile,  according  to 
Musgrave  and  Clegg,  and  this  may  also  be  true  of  other 
trypanosomes.  Its  motility  is  moderate  and  eel-like.  It 
differs  from  the  trypanosome  of  rats  {T.  lewisi)  in  its 
larger '  diameter    and    in    its    greater    pathogenicity ;    T. 


682 


INFECTION     AND     IMMUNITY. 


Donriiie. 


Mai   de 
Caderas. 


InfectioiiH 
of  Other 
AninialH. 


evansi  is    pathogenic   for   "nearly   all    animals."     It   is 
longer  than  T.  brucei. 

Surra  affects  horses  chiefly,  and  has  caused  immense 
losses  in  India  and  in  the  Philippine  Islands.  In  India 
it  is  certainly  transmitted  by  certain  flies,  and  the  same 
probably  is  true  in  the  Philippines.  Musgrave  and  Clegg 
demonstrated  also  that  fleas  may  be  of  great  importance 
as  carriers.  By  this  means  they  were  able  to  transfer 
the  disease  from  dog  to  dog,  rat  to  rat,  and  rat  to  dog. 
They  frequently  found  the  parasites  in  native  rats  and 
believe  that  this  animal  may  serve  as  a  host  in  which  the 
disease  is  maintained.  Cattle  are  susceptible  to  infec- 
tion, but  the  disease  is  less  malignant  in  them  and  runs 
a  long  course;  hence,  they  may  be  an  important  factor 
in  maintaining  an  epidemic.  The  disease  is  also  trans- 
mitted from  horse  to  horse.  In  India,  camels,  elephants 
and  buffaloes  also  suffer  from  the  disease.  Surra  resem- 
bles nagana  in  its  clinical  and  anatomic  aspects. 

Doflein  gave  the  name  of  Trypanosoma  equiperdum  to 
an  organism  described  by  Rouget  in  horses  and  asses 
suffering  from  dourine.  Laveran  and  Mesnil  call  it  T. 
rougetii.  According  to  Rouget,  the  parasite  resembles 
T.  Irucei  closely.  Doflein  (1901)  states  that  a  nucleus 
and  vacuole  have  not  been  seen.  Dourine  occurs  in 
Algiers,  southern  France,  Navarre  and  in  the  Pyrenees 
districts  of  France  and  Spain.  The  infection  is  trans- 
mitted by  coitus  and  is  limited  largely  to  animals  which 
are  used  for  breeding.  Ulcerations,  particularly  of  the 
genitals,  are  characteristic.  That  it  is  not  transmitted 
by  insects  may  be  due  to  the  absence  of  suitable  insects 
from  these  localities.  The  identity  of  dourine  with 
surra  or  nagana  is  not  yet  determined.  It  is  said  to  be 
more  chronic  than  surra.  Doflein  recognizes  the  organ- 
ism as  an  independent  parasite.  Infection  may  be  trans- 
ferred to  dogs,  white  mice  and  other  animals. 

Trypanosoma  equinam  (Voges)  or  T.  elmassianii  is 
the  parasite  found  in  mal  de  cacleras,  a  disease  of  horses 
in  South  America,  resembling  surra,  nagana  and  dourine. 

Two  different  species  have  been  found  in  the  blood  of 
South  African  cattle:  T.  theileri  (Bruce,  1902)  and  T. 
transvaaliense  (Laveran  and  Mesnil,  1902).  The  char- 
acteristic  feature   of   the   latter   is   the   location   of   the 


CULTIVATION    OF    TRYPANOSOMES. 


683 


centrosome  near  the  nucleus  near  the  center  of  the  para- 
site. The  following  trypanosomes  are  found  in  fish: 
T.  colitis,  T.  carassii,  T.  remakii,  T.  solece,  T.  horrellii; 
the  following  in  birds :  T.  avium,  T.  eberthii.  T.  balbianii 
occurs  in  oysters,  T.  rotatorium  in  frogs. 

Between  various  animals  and  the  different  try- 
panosomes a  number  of  examples  of  natural  im- 
munity are  known.  The  extent  to  which  man  is 
susceptible  to  sleeping  sickness  is  not  known,  but 
since  the  disease  may  occur  in  Europeans  as  well 
as  in  native  Africans,  it  is  probable  that  suscepti- 
bility is  general.  Laveran  and  Mesnil  state  that 
sheep,  deer  and  cattle  which  have  recovered  from 
nagana  have  an  active  immunity  to  the  disease, 
and  it  is  thought  that  the  immunity  of  some  ani- 
mals (e.  g.,  cow)  may  be  increased  by  injecting 
infected  blood.  Koch,  and  also  Schilling,  have  at- 
tempted to  render  trypanosomas  suitable  for  vacci- 
nation by  passing  them  through  asses,  and  a  cer- 
tain degree  of  success  was  reported.  The  serums 
of  actively  immunized  animals  do  not  exert  a  pro- 
nounced protective  or  curative  action,  although 
they  may  in  some  instances  prolong  the  incubation 
period.  Human  serum  has  a  certain  protective 
and  curative  power  for  rats  and  mice  which  have 
been  inoculated  with  the  parasite  of  nagana.  In 
some  instances  immime  and  normal  serums  kill 
trypanosomes,  as  shown  by  rapid  loss  of  mobility. 

A  most  interesting  bit  of  experimental  therapy 
is  that  of  Ehrlich  and  SaclTs  in  curing  and  pro- 
tecting mice  against  mal  de  caderas  by  injecting 
and  feeding  "trypanroth,"  a  S3mthetic  dye.  The 
dye  was  less  efficient  in  experimental  nagana  and 
in  trypanosomatic  infections  of  rats,  guinea-pigs 
and  doos.     The  immunitv  and  cure  established  in 


Iiitninnity 


"Trypan- 
rotli." 


G84  IXFECTIOX     AND     IMMU:^ITY. 

this  way  is  ven-  temporary  and  is  to  be  referred 
to  a  reaction  caused  in  the  body  rather  than  to  a 
direct  effect  on  the  parasites.  The  latter  are  not 
killed  by  the  dye  in  test-tube  experiments.  ^^One 
may  conceive  of  the  action  of  a  trypanroth  in  this 
way,  that  as  a  result  of  a  fresh  injection  of  the 
d3'e  a  reaction  takes  place  in  the  animaPs  body, 
which  leads  to  the  death  of  the  trypanosomes ;  the 
reaction  products  possess  only  a  temporary  char- 
acter and  cease  to  be  formed  as  soon  as  the  dye 
is  disposed  of.^' 

Laveran  reports  a  favorable  influence  on  try- 
panosomiasis in  mice  and  rats  by  a  combined  treat- 
ment with  sodium  arsenite  and  "trypanroth. '^ 

When  a  dose  of  trypanroth  which  is  insufficient 
to  cause  complete  disappearance  of  trypanosomes 
is  given,  the  remaining  organisms  become  immune 
to  the  further  action  of  the  drug.  It  is  of  impor- 
tance, therefore,  to  give  the  largest  dose  which  is 
non-toxic  for  the  patient.  At  present,  two  new 
preparations  of  Ehrlich,  trypanosan  and  agridi- 
num,  which  are  highly  trypanocidal,  are  being 
tried  in  combiuation  with  arsenophenylglycin. 

III.  TEXAS   FEVER. 

Texas  fever  of  cattle  may  be  considered  briefly  as  a 
well-established   example  of  piroplasmosis, 

Th.  Smith  and  Kilbourne  (1893)  discovered  a  pear- 
Parasite,  shaped  protozoon  {Pyroplasma  hovis) ,  which  occurs  in 
pairs  in  the  erythrocytes  of  infected  cattle.  The  para- 
site measures  from  2  to  4  microns  long  by  1.5  to  2 
microns  broad,  the  smaller  ends  of  the  pairs  lying  in 
apposition.  The  organisms  have  a  rapid  but  rather  coarse 
ameboid  movement.  About  1  per  cent  of  the  corpuscles 
are  invaded  ordinarily,  but  in  fatal  cases  the  proportion 
may  rise  from  5  to  10  per  cent.  The  method  of  prolifera- 
tion of  the  parasite  has  not  been  followed  out  definitely. 


The 


riJXAS    FEVER.  085 

According  to  Smith  and  Kilboiirne,  numerous  minute 
motile  forms  (coccus-like  bodies)  penetrate  the  corpus- 
cles and  eventually  reach  the  pear-shaped  form.  The 
breaking  up  of  the  adult  pear-shaped  parasites  into  such 
small  forms  has  not  been  observed. 

A  characteristic  symptom  of  Texas  fever  is  the  pro- 
nounced hemoglobinuria  which  has  given  to  the  disease 
the  additional  name  of  hemoglobinuric  fever. 

The  disease  is  transmitted  by  means  of  a  tick  {Boophi- 
lus  bovis ) .  The  six-legged  larvae  fill  themselves  with 
blood,  and  in  about  eight  days  have  been  changed  into 
eight-legged  nymphse.  In  eight  days  more  they  have 
changed  into  fully-formed  sexual  animals,  and,  after 
filling  themselves  with  blood  and  after  having  been  im- 
pregnated, they  drop  off  the  cattle  and  lay  their  eggs. 
Larva)  hatch  from  the  eggs  in  from  3  td  4  weeks,  and 
the  former  arc  again  i-eady  to  attacli  tliemselves  to 
cattle  ( cited  from  Kossel ) .  Inasmuch  as  infected  ticks 
transmit  the  parasites  to  their  offspring,  the  bites  of  the 
larvae  are  able  to  give  rise  to  the  disease  in  cattle.  A 
mature  tick  may  deposit  from  2,000  to  4,000  eggs.  It 
has  not  been  possible  to  transmit  the  disease  to  otlier 
species. 

The  disease  is  endemic  in  the  southwestern  states.  Transmission. 
and  the  cattle  in  that  region  are  supposed  to  acquire  an 
immunity  similar  to  that  described  by  Koch  in  relation 
to  malaria.  Presumably  the  cattle  first  acquire  the  dis- 
ease when  they  are  young,  and  those  which  withstand  it 
show  resistance  to  the  infection  in  later  life.  Cattle 
from  uninfected  districts  are  more  susceptible  than  those 
coming  from  localities  in  which  the  disease  is  endemic, 
and  the  latter  even  when  apparently  healthy  may  intro- 
duce the  disease  into  new  herds.  This  is  done  through 
transportation  of  the  ticks. 

Partially  successful  attempts  at  active  immunization 
have  been  made,  and  in  Australia  this  is  practiced  on 
a  fairly  extensive  scale.  Five  to  ten  cubic  centimer?  of 
blood,  taken  from  an  infected  animal,  during  the  course 
of  the  disease  or  after  recovery  has  been  established,  are 
injected  into  non-immune  cattle.  The  disease  is  thereby 
reproduced  in  the  latter  with  typical  parasites  in  the 
blood.     If  the  blood  is  taken  from  animals  which  have 


686 


INFECTION     AND     IMMUNITY 


recovered,  a  milder  infection  results  than  when  the  blood 
of  an  actively  infected  animal  is  used  (Pound,  cited  by 
Kossel ) .  The  resulting  immunity  is  not  an  absolute  one, 
however,  and  the  percentage  of  mortality  is  fairly  high. 
According  to  Dodson,  the  serum  of  animals  which  have 
completely  recovered  has  no  protective  power  for  other 
animals. 

For  prophylaxis  it  is  important  to  free  the  cattle 
from  ticks  (as  by  an  oil  bath)  and  to  avoid  infected 
fields.  If  cattle  are  kept  from  an  infected  pasture  for 
two  years,  the  ticks  die  out  very  largely  ( Morgan ) . 

IV.    AMEBIC   DYSENTERY. 

Ameba.  Amebas  are  unicellular  animal  organisms  which 
contain  one  or  more  nuclei,  a  "contractile"  vacuole, 
a  granular  endoplasm  and  a  tougher  more  hyaline 
ectoplasm,  having  the  power  of  locomotion  by 
means  of  pseudopodia  or  by  a  gradual  flowing  for- 
ward of  the  cytoplasm.  They  nourish  themselves 
by  digesting  bacteria  and  other  lower  organisms  or 
solid  particles  of  decaying  matter,  which  they  in- 
gest after  the  manner  of  phagocytes.  They  pro- 
liferate by  division  of  an  adult  cell  into  two  daugh- 
ter cells,  and  certain  of  them  reach  a  cystic  stage 
in  which  hundreds  of  endospores  are  formed 
{Amodba  proteus).  Some  of  them  utilize  higher 
animals  as  hosts  only  occasionally,  while  others 
are  known  only  as  parasites.  They  frequently  are 
encountered  in  the  intestines  of  mice,  frogs  and 
other  animals. 
DiBtribution.  AmobsB  are  widely  distributed  in  nature,  exist- 
ing to  the  depth  of  2  meters  in  tropical  soils,  in 
the  water  of  springs  and  wells  and  practically  all 
surface  waters  (hot  countries) ,  and  in  stagnant  or 
sluggish  waters  in  higher  altitudes.  They  exist  on 
hay,  fruits  and  vegetables  of  all  kinds,  especially 


AMEBIC   DYSENTERY.  G87 

those  grown  on  or  near  the  earth;  e.  g.^  beets  and 
lettuce. 

Encystation  takes  place  under  certain  unfavor-  Resistance. 
able  conditions^  and  in  this  condition  the  parasites 
withstand  a  temperature  of  — 15°  C.  for  twenty- 
five  days  (Musgrave  and  Clegg),  and  desiccation 
for  from  ten  to  fifteen  months.  A  temperature  of 
50°  C.  kills  the  vegetable  and  encysted  forms. 
Sunlight  for  three  hours  and  the  a;-ray  kill  them 
readily  in  the  vegetable  form,  but  not  so  readily 
when  they  are  encysted.  Most  chemical  bacteri- 
cides destroy  them,  although  they  show  a  particu- 
lar resistance  to  alkalies,  even  20  per  cent,  sodium 
hydrate  (Frosch),  and  strong  acids.  They  resist 
the  action  of  0.2  per  cent,  hydrochloric  acid,  i.  e., 
the  acidity  of  the  stomach  contents.  Quinin 
(1/2500  of  the  hydrochlorate)  is  strongly  germi- 
cidal for  Amoeba  coli. 

Under  artificial  conditions  amebae  proliferate  cultivation. 
in  the  presence  of  other  micro-organisms,  and 
suitable  mixtures  they  may  be  kept  alive  in- 
definitely on  slightly  alkaline  bouillon  agar. 
The  only  condition  in  which  amebse  are  found 
unassociated  with  bacteria  is  in  the  liver  ab- 
scesses which  occur  as  a  complication  of  amebic 
dysentery.  It  is  true  that  the  bacteria  may  have 
been  present  originally,  but  in  their  absence  it  is 
supposed  that  enzymes  normally  present  in  the 
liver  stimulate  the  growth  and  proliferation  of  the 
parasites.  Amebse  show  a  peculiar  selective  property 
for  certain  bacteria,  although  their  affinities  may 
be  gradually  modified.  Amoeba  coli  apparently  pre- 
fers those  organisms  which  flourish  in  the  human 
intestines  (B.  coli,  B.  typhosus,  Sp.  cholerce.  Staph, 
pyog.  aureus).     Almost  any  strain  will,  however, 


688 


IM'ECTIOX     AXD     IMMUNITY. 


Anieba 
Coli. 


grow  with  a  variety  of  bacteria.  Growth  occurs 
only  on  the  surface  of  the  agar  plates.  When  a 
pure  strain  of  ameba  is  grown  with  a  single  species 
of  bacterium  the  culture  is  spoken  of  as  a  "pure 
mixed  culture." 

Amebic  dysentery  is  primarily  a  disease  of  the 
tropics,  where  the  natural  conditions  are  favorable 
for  the  growth  of  the  amebae  and  their  conveyance 
to  man. 

First  found  by  Lambl  (1860),  then  by  Cunning- 
ham and  Lewis  (1870),  the  organisms  were  de- 
scribed more  accurately  and  given  the  name  of 
Amoeba  coli  by  Losch  (1875).  Losch  recognized 
them  as  the  cause  of  a  chronic  form  of  dysentery, 
but  it  was  Kartulis,  in  particular,  who  found  the 
ameba3  constantly  in  the  discharges  and  ulcers  of 
the  disease,  and  also  in  the  liver  abscesses  which 
accompany  the  infection.  Since  amebae  demand 
the  presence  of  living  bacteria  for  their  growth, 
their  independent  pathogenic  nature  has  been  ques- 
Pathoge-  tioned  by  many  who  assume  that  the  bacteria  are 
the  primary  agents  in  causing  the  intestinal  lesions 
and  that  the  amebse  are  only  incidental  or  second- 
ary factors.  Many  others,  and  particularly  Mus- 
grave  and  Clegg,  consider  that  amebae  have  essen- 
tial pathogenic  properties  and  are  the  primary 
agents  in  producing  amebic  dysentery.  By  the 
feeding  of  encysted  cultures  grown  with  other  or- 
ganisms, Musgrave  and  Clegg  reproduced  the  dis- 
ease typically  in  many  monkeyj.  In  one  instance 
the  amebae  were  fed  in  conjunction  with  cholera 
vibrios;  typical  dysentery  developed  and  during 
the  course  of  the  disease  the  vibrios  disappeared 
from  the  stools.  The  vibrio  alone  proved  to  be 
non-pathogenic  when  fed  to  monke3^s,  and  on  this 


nicity. 


AMEIiW   DYSENTERY.  089 

account  they  held  the  amebse  to  be  the  sole  cause 
of  the  dysentery. 

According  to  Schaudinn  and  Craig,  ameboe  are 
of  two  types.  One  of  non-pathogenic  character 
(Eniamwba  coli)  found  by  Craig  in  50  per  cent, 
of  normal  stools;  the  other  pathogenic  (Entamceba 
liistolyiica) . 

According  to  Schaudinn,  the  two  organisms  di!'-   i.esions. 
fer  in  morphology  and  method  of  reproduction. 
Walker  fails  to  confirm  these  observations. 

The  principal  lesions  occur  in  the  large  intes- 
tine, in  which  are  found  round  or  oval  ulcers  with 
infiltrated  or  undermined  edges.  The  ulcers  may 
increase  in  size,  or  coalesce  with  others,  and  cause 
the  sloughing  of  large  areas  of  the  mucosa  or  even 
of  the  muscular  coats.  The  organisms  are  found 
in  the  intestinal  contents,  on  the  surface  of  the 
ulcers,  in  the  infiltrated  base  and  edges,  and  in  the 
underlying  tissues.  They  have  been  found  as- 
sociated with  both  chronic  and  acute  appendi- 
citis. Amebic  liver  abscesses  are  not  infrequent 
in  those  regions  in  which  the  disease  is  endemic. 
The  organisms  probably  extend  to  the  liver  from 
the  intestines  through  the  lymphatic  or  portal 
vessels.  Not  infrequently  the  association  of  the 
amebse  with  bacteria  is  missed  in  the  abscesses, 
and  in  these  instances  a  "cold"  abscess  containing 
much  necrotic  material  and  detritus  is  produced. 
If  contaminated  with  bacteria  the  abscesses  have 
a  more  purulent  character. 

Suitable  prophylaxis  against  amebic  infection  i?    Prophylaxis. 
suggested  by  the  known  distribution  of  these  or- 
ganisms.   Of  principal  importance  is  the  use  of  fil- 
tered or  boiled  waters  and  the  avoidance  of  un- 


690  IXFEGTIOX     AJD     IMMUNITY. 

cooked  vegetables  in  regions  in  which  the  disease 
is  endemic,  as  in  the  Philippine  Islands. 
immnnity.  From  the  fact  that  foreigners  going  into  tropical 
countries  are  more  susceptible  to  infection  than  the 
natives,  it  is  concluded  that  the  latter  have  some 
natural  (or  acquired)  immunity  to  the  disease. 
Children  are  said  to  be  less  susceptible  than  adults 
and  in  them  the  disease  yields  to  treatment  more 
easily.  There  is  no  serum  therapy  for  the  infec- 
tions. The  salts  of  quinin  in  strengths  of  from 
1-1500  to  1-750  are  amebicidal  when  injected  into 
the  colon. 

V.    SARCOSPORIDIA. 

Morpboiogry.  Sarcosporidia  are  unicellular  parasites  which  are 
found  within  the  muscle  cells  of  some  animals,  but 
very  rarely  in  man.  They  are  more  or  less  tubular 
or  oval  in  shape  and  are  frequently  referred  to  as 
Miescher's  tubules.  Their  size  varies  greatly  and 
certain  species  may  reach  a  length  of  two  centi- 
meters. When  well  developed  they  possess  two 
capsules — a  dense  outer  capsule,  which  is  perfor- 
ated with  minute  canals  ( ?)  directed  toward  the 
center  of  the  parasite,  and  an  inner  thin  hyalin 
membrane.  Both  represent  differentiated  ecto- 
plasm (Doflein).  The  endoplasm,  even  in  young 
cells,  gives  rise  to  numerous  small  nucleated 
spheres  (pansporoblasts),  which  increase  in  size 
and  each  of  which  eventually  becomes  multinu- 
cleated and  forms  numerous  kidney  or  sickle- 
shaped,  nucleated  sporoblasts.  Each  sporoblast 
finally  gives  rise  or  is  changed  into  a  well-charac- 
terized spore  with  a  membrane  and  a  nucleus. 
This  process  takes  place  first  in  the  central  part 
of  the  parasite,  but  eventually  extends  to  the  ends 


BALANTIDWM    COLL  691 

as  well.    The  central  part  of  the  old  parasites  con 
tains  only  the  empty  network  of  endoplasm,  the 
spores  having  disappeared,  and  a  section  at  this 
point  strongly  resembles  that  of  a  tubule. 

The  parasites  are  nourished  through  osmosis. 
None  of  the  forms  have  definite  motility.  When 
the  parasite  outgrows  the  muscle  cell  which  con- 
tains it,  it  is  freed  and  becomes  an  intercellular 
parasite.  Eather  vague  references  are  made  to 
tumor-like  formation  as  a  consequence. 

Sarcosporidia  have  been  found  only  in  verte-  occurrence. 
brates,  particularly  in  mammals;  most  often  in 
sheep  and  hogs,  but  also  in  the  horse,  ox,  mouse, 
rat.  The  muscles  adjacent  to  the  alimentary  tract 
are  involved  principally  (esophagus,  intestines, 
diaphragm  and  abdominal  muscles)  and  on  this 
account  it  is  supposed  that  infection  takes  place 
through  the  intestines.  The  exact  method  of  in- 
oculation is  not  known. 

Sarcocystis  lindemanni  (Sarcocystis  hominis  or 
Gregarina  lindemanni)  is  the  only  sarcosporidium 
definitely  identified  in  man.  The  parasites  were 
as  large  as  1.6  millimeters  long  and  170  microns 
broad.  They  possessed  a  thin  capsule,  thickened 
at  the  ends.  The  spores  were  banana-shaped  and 
from  8  to  9  microns  long.  The  organisms  were 
found  in  the  muscles  of  the  larynx. 

VI.    BALANTIDIUM  COLI. 

B.  GoU  is  an  infusorian  (ciliate),  with  a  more 
or  less  oval  body,  mouth  opening  and  a  short 
pharynx,  is  covered  rather  uniformly  with  short 
cilia,  and  presents  longitudinal  striations.  It  con- 
tains a  bean-shaped  chief  nucleus  and  a  secondary 
nucleus  and  two  vacuoles  on  the  right  side.  It  meas- 


692  INFECTlOy     AND     IMMUNITY. 

ures  from  70  to  100  microns  in  lengths  and  from 
50  to  70  in  breadth.  Proliferation  is  through  sim- 
ple division.  Conjugation  has  been  noted.  Invo- 
lution cysts  are  sypherical  and  surrounded  by  a 
dense  membrane. 
patiiogenic  The  parasite  is  found  in  the  intestines  of  the  hog 
as  well  as  m  man^  and  the  lormer  may  be  its  nor- 
mal host.  It  occurs  also  in  sewage  waters  and  has 
been  found  in  drinking  water.  Infections  have 
been  noted  in  those  having  nothing  to  do  with  hogs. 
The  organisms  may  reach  the  intestines  of  man  in 
an  encapsulated  state  (?).  It  is  found  in  diar- 
rheal conditions  in  man  rarely,  and  the  question 
is  still  open  as  to  whether  the  parasite  is  able  to 
cause  enteritis  independently  or  whether  it  merely 
aggravates  and  prolongs  an  enteritis  due  to  other 
causes. 

The  cecum  and  colon  show  the  principal  changes 
at  autopsy,  and  are  of  an  inflammatory  and  ulcera- 
tive nature. 

A  smaller  species,  B.  minutum,  has  also  been 
observed  in  the  intestines  of  man. 

VII.     CERCOMONAS  INTESTINALIS. 

Morphology.  This  Organism  is  small  and  colorless,  the  form 
spherical  or  oval.  The  single  flagellum  is  for  the 
most  part  very  large  and  is  situated  at  the  anterior 
end  (in  the  direction  in  which  the  parasite 
moves)  ;  the  posterior  end  is  long  drawTi  out  and 
is  subject  to  changes  in  form.  Sharp  pseudopodia 
are  sometimes  formed.  The  nucleus  lies  in  the 
anterior  half  of  the  body,  and  either  here  or  on  the 
sides  are  one  or  more  vacuoles.  A  mouth  opening 
is  not  differentiated,  but  at  the  base  of  the  flagel- 
lum food  is  taken  in  at  a  particular  point  through 


TRICHOMONAS.  093 

a  vacuole.  Proliferation  takes  place  through  con- 
jugation, binary  division  and  the  formation  of 
swarm  spores  ( ?)  within  encysted  forms.  They 
abound  in  fresh  water  and  in  infusions  of  grasses. 

They  are  not  of  great  parasitic  importance,  al-  significance. 
though  cercomonas  has  been  found  in  the  intes- 
tines, especially  in  inflammatory  conditions  (chol- 
era, typhoid),  in  pulmonary  gangrene,  putrid  plu- 
ritis,  and  several  forms  have  been  observed  in  other 
animals. 

It  is  not  yet  certain  that  cercomonas  may  be  an 
independent  cause  of  enteritis. 

VIII.     TRICHOMONAS. 

Eather  small,  of  a  general  pear-shape,  rounded  Morpuoiosy. 
or  pointed  anterior  end,  and  possessing  three  or 
four  long  flagella.  When  only  three  flagella  are 
present  an  undulating  membrane  surrounds  the 
body  like  a  spiral  beginning  at  the  base  of  the 
flagella  and  may  prolong  itself  into  a  flagellum. 
The  posterior  extremity  is  moderately  pointed,  a 
nucleus  lies  in  the  anterior  end,  and  toward  the 
posterior  are  several  non-contractile  vacuoles. 
Methods  of  proliferation  unknown  (Doflein). 

Two  species  are  found  in  man.  Trichomonas 
vaginalis:  possesses  three  flagella  and  an  undu- 
lating membrane,  and  is  of  large  size  (from  15  to 
25  microns  in  length).  It  is  found  in  the  vaginal 
mucus,  when  of  acid  reaction,  in  a  large  percent- 
age of  women  (Dolflein),  particularly  in  vaginal 
catarrhs.     It  disappears  in  an  alkaline  reaction. 

Trichomonas  hominis  s.  intestinalis :  also  pos- 
sesses three  flagella  and  an  undulating  membrane, 
but  is  smaller  than  T.  vaginalis.  It  is  found  as  a 
parasite  in  the  human  intestines,  particularly  in 


694  INFECTION     AND     IMMUNITY. 

diarrheas  (typhoid,  cholera,  mucous  colitis,  etc.,) 
and  inhabits  especially  the  upper  and  middle  por- 
tions of  the  intestines.  It  is  evacuated  in  consid- 
eral  numbers  following  administration  of  cathar- 
tics. It  appears  not  to  be  of  much  pathogenic  sig- 
nificance, but  finds  in  the  liquid  stools  and  in  an 
alkaline  reaction  conditions  which  favor  its  prolif- 
eration. It  may  be  transmitted  as  a  contagion 
(Epstein). 

Other  species  of  trichomonas  occur  in  the  intes- 
tines of  different  animals. 
other  other  less  important  flagellates  are:  Lamhlia 
aee  a  es.  ^^^^^^{^^1^^^  fouud  in  the  intestines  of  many  ani- 
mals and  in  man  in  Germany,  Italy,  Eussia  and 
Sweden;  Bodo  urinarius  (Cystomonas  urinarius, 
Flagiomonas  urinaria),  found  in  the  urine  in  cys- 
titis (Kiinstler). 

IX.    COGCIDIOSIS. 

Coccidia  are  essentially  cell  parasites,  preferring 
the  epithelial  cells  of  the  intestines  and  liver,  al- 
though they  may  be  carried  to  other  organs.  They 
have  an  alternating  asexual  and  sexual  cycle  of 
development.  The  young  sickle-shaped  and  nu- 
Life  Cycles,  clcated  sporozoitc  penetrates  an  epithelial  cell, 
grows  in  size,  and  the  nucleus  subdivides  many 
times  to  form  new  young  cells,  which  eventually 
escape  again  as  sickle-shaped  sporozoites.  This 
asexual  process  is  called  schizogony.  Several  stages 
of  schizogony  may  follow  successively,  but  event- 
ually the  organisms  lose  their  proliferative  power 
unless  they  are  fortified  by  a  sexual  cycle.  In  the 
sexual  cycle  (sporogony)  some  of  the  sporozoites 
become  differentiated  into  larger  granular  cells 
(female)    and   others   into   smaller   cells    (male). 


COCGIDIOSIS. 


695 


Of  these  two  cells  the  male  eventually  divides  into 
many  flagellated  microgametes,  each  of  vi^hich  is 
able  to  penetrate  and  fertilize  a  female  cell  (macro- 
gamete).  The  female  cell  then  forms  a  capsule, 
becomes  an  oocyst,  divides  into  sporoblasts,  each 
of  which  eventually  forms  sickle-shaped  spores,  species. 
which  when  liberated  are  again  called  sporozoites. 
Several  species  are  recognized,  depending  on  the 
number  of  spores  formed  by  the  oocyst.  In  some 
instances  the  spore  formation  takes  place  in  the 
outer  world,  and  when  the  oocysts  are  ingested  the 
sporozoites  are  liberated. 

Coccidium  cuniculi  s.  oviforme  is  a  frequent 
parasite  in  the  intestines  and  liver  of  the  rabbit, 
occurs  occasionally  in  the  same  organs  in  man  from 
association  with  rabbits  (?),  and  causes  a  hemor- 
rhagic dysentery  in  the  cattle  of  some  countries 
(Switzerland).  Horses,  goats  and  swine  may  also 
be  infected. 

Spore  formation  takes  place  outside  the  host. 
The  oocyst  is  discharged  in  the  feces  and  produces 
four  spores,  each  of  which  forms  two  sporozoites. 
A  new  host  is  infected  by  the  ingestion  of  spores. 

Diarrhea  and  emaciation  result  from  infection 
of  the  intestines,  and  in  the  liver  cheesy  nodules 
(coccidia  nodules)  are  formed,  containing  para- 
sites, degenerated  cells  and  proliferated  epithe- 
lium. A  papillomatous  proliferation  of  the  epi- 
thelium of  the  bile  passages  and  intestines  may  be 
produced. 

Coccidium  'bigeminum,  a  coccidium  in  which 
the  oocyst  divides  into  two  spore-containing  cysts, 
has  been  found  in  man  several  times. 


Results   of 
Infection. 


696  INFECTION     AND     IMMUNITY. 

X.     KALA-AZAR. 

Kala-azar,  or  febrile  splenomegaly,  is  a  tropical 
disease,  especially  of  India  and  China,  associated 
with  great  enlargement  of  the  spleen,  often  of  the 
liver,  extreme  cachexia  and  anemia.  The  disease 
was  formerly  looked  on  as  a  malarial  cachexia. 

Both  Leischman  and  Donovan  described  bodies 
in  stained  preparations  of  splenic  pulp  and 
ascribed  to  them  an  etiological  significance.  These 
observations  have  l^een  confirmed  repeatedly.  The 
bodies  are  small  round  mass  of  cytoplasm,  which 
with  the  Eomanowski  stain  is  colorless.  Two 
masses  of  chromatin^  one  much  smaller  than  the 
other,  take  a  purplish  stain.  The  whole  body  is 
from  2  to  3  microns  in  diameter.  Eogers  suc- 
ceeded in  cultivating  the  organisms  in  blood 
slightly  acidified  with  citric  acid  and  incubated  at 
22°  C.  In  this  way  a  flagellated  form  was  ob- 
tained which  is  similar  to  trypanosomes  in  mor- 
phology. The  classification,  however,  is  not  yet 
certain.  The  organism  is  distributed  throughout 
the  body,  but  is  most  numerous  in  the  spleen,  bone 
marrow,  and  liver. 

Patton  succeeded  in  obtaining  growth  of  the 
parasite  in  tlie  stomach  of  the  bed  bug,  and  it 
seems  probable  that  transmission  occurs  in  this 
way.  Eogers,  acting  on  this  supposition,  was  able 
to  reduce  the  number  of  cases  by  ridding  the 
houses  of  bed  bugs. 


CHAPTEK  XXX 
GROUP  VII 

DISEASES   OF  DOUBTFUL  OK  UNKNOWN   ETIOLOC.Y. 


I.     HYDROPHOBIA. 

Following  the  investigations  of  Pasteur,  in 
which  it  was  found  that  the  virus  of  hydrophobia 
exists  in  the  central  nervous  system  in  pure  cul- 
ture, the  conditions  seemed  favorable  for  the  dis- 
covery of  the  specific  agent.  As  in  the  case  of 
many  other  diseases,  various  bacilli,  cocci,  yeasts 
and  so-called  protozoa  have  been  described  as  the 
cause,  but  satisfactory  proof  of  their  etiologic  role 
has  not  been  provided. 

Certain  protozoon-like  bodies  (Negri  bodies)  Bodies  of 
found  by  Negri  in  the  ganglionic  cells,  are  of  a 
suggestive  nature.  Their  average  diameter  is 
about  five  microns,  but  it  varies  between  one  and 
twenty-seven  microns.  They  possess  a  "round, 
oval,  elliptical,  or  coarse  triangular  form"  (Marx), 
are  differentiated  into  a  central  granular  and  a 
peripheral  structure  and  may  be  surrounded  by  a 
doubly-contoured  membrane.  Negri  considers  these 
bodies  specific  for  hydrophobia  and  reliable  as  a 
basis  for  anatomic  diagnosis.  They  are  found  par- 
ticularly in  the  pyramidal  cells  in  the  cornu  Am- 
monis,  the  cells  of  Purkinje  in  the  cerebellum, 
and  the  large  cells  of  the  cerebral  convolutions. 
Many  others  have  confirmed  the  findings  of  Negri, 
and  it  is  now  generally  conceded  that  the  bodies 


698  INFECTION     AND     IMMUNITY. 

are  specific  for  rabies,  and  of  great  diagnostic 
value.  Against  the  hypothesis  that  these  bodies 
are  the  cause  of  hydrophobia,  the  following  points 
are  cited:  The  distribution  of  the  Negri  bodies 
does  not  correspond  with  the  greatest  concentra- 
tion of  the  virus  in  the  nervous  tissue,  the  latter 
being  most  abundant  in  the  medulla  and  pons 
where  the  Kegri  bodies  are  encountered  rarely.  They 
present  certain  analogies  with  "protoplasmic  in- 
clusions" seen  in  other  conditions,  as  in  carcinoma, 
variola,  etc.  Eemlinger  found  that  the  virus 
passes  through  appropriate  Berkefeld  filters,  and 
for  this  reason  Schiider  holds  that  the  bodies  of 
Negri,  being  too  large  for  filtration,  can  not  be 
considered  as  the  specific  organism.  The  view  of 
Schiider  may  be  criticized,  since  the  smallest 
Negri  bodies  are  so  minute  that  their  filtration 
would  seem  to  be  possible.  Nevertheless,  it  must 
remain  doubtful  whether  bodies  one  micron  in  di- 
ameter, the  proliferation  of  which  has  not  been 
proved,  may  be  considered  as  parasites.  The  hy- 
pothesis of  Negri  is  hardly  on  a  satisfactory  basis 
at  present.  Eemlinger  considers  the  bodies  as 
"involution  forms"  of  the  tissue  cells  which  have 
been  invaded  by  the  true  parasite. 
PiiteraMiity  The  filtcrabilitv  of  the  virus  ars^ues  for  its  ultra- 
microscopic  size.  By  means  oi  nitration  one  may 
isolate  it  even  from  brains  which  are  badly  decom- 
posed, and  the  method  renders  it  possible  to  ob- 
tain pure  cultures  for  purposes  of  immunization. 
Inoculation  with  filtered  virus  is  sometimes  fol- 
lowed by  a  prolonged  incubation  period  which  may 
depend  on  the  retention  of  many  of  the  organisms 
by  the  filter.  A  similar  effect  was  produced  by 
Hogyes  by  inoculating  with  diluted  virus. 


HYDROPHOBIA.  699 

By  prolonged  centrifugation  of  an  emulsion  of 
infected  nervous  tissue  the  overlying  fluid  loses  its 
infectiousness. 

The  possibility  that  tlie  organism  secretes  a  sol-  Toxin. 
uble  toxin  is  important  from  the  standpoint  of  im- 
munization. A  number  of  ol)sei'vers,  particularly 
Babes^  and  Heller  and  Bertarelli,  noted  that  fil- 
trates of  infected  nervous  tissue  sometimes  cause 
emaciation,  paralyses  and  eventual  death  without 
producing  a  disease  which  is  transmissible  to  other 
animals.  The  organism  is  without  doubt  toxic, 
but  these  results  give  us  no  idea  of  the  nature  of 
the  toxin. 

The  nrus  of  hydrophobia  as  contained  in  the  Resistance 
central  nervous  system  of  infected  animals  exhib- 
its strong  resistance  to  chemical  germicides.  Five 
per  cent,  carbolic  acid  destroys  it  in  fifty  minutes, 
1  per  cent,  in  three  hours,  and  1-1000  corrosive 
sublimate  in  three  hours  (Marx).  It  resists  the 
action  of  putrefactive  bacteria,  and  has  been  found 
virulent  in  animals  which  had  been  buried  for  two 
to  four  weeks,  even  when  the  brain  was  putrid.  Di- 
rect sunlight  destroys  it,  however,  in  a  very  short 
time.  According  to  Tizzoni  and  Bongiovanni,  the 
rays  of  radium  have  a  destructive  action  on  the 
virus.  It  is  less  resistant  to  heat,  being  destroyed  in 
one-half  hour  at  a  temperature  of  52-58°  C. 
(Hogyes)^  but  is  not  affected  by  the  temperature 
of  liquid  air  for  three  months.  Chlorin  destroys 
it  very  rapidly.  It  is  gradually  weakened  by 
desiccation,  as  first  shown  by  Pasteur,  the  virus 
probably  undergoing  gradual  death  rather  than 
mere  attenaation.  It  is  said  to  be  attenuated  by 
the  action  of  the  gastric  juice  and  by  the  bile. 
When  the  nervous  tissue  is  emulsified  in  glycerin, 


700  INFECTIOy     A^W     IMMUNITY. 

virulence  is  retained  for  months  (Roux).  On  the 
other  hand,  glycerin  appears  to  destroy  the  viru- 
lence of  filtrates  (Di  Vestea). 

street  Virus       Pastcur  gave  the  name  of  street  v-^us    (virui 
Virus,   de  rue)  to  that  obtained  from  the  nervous  tissue  of 
dogs  in  which  the  disease  develops  spontaneously. 
When  the  street  virus  is  injected  subdurally  into 
the  rabbit  the  latter   develops  hydrophobia   only 
after  an  incubation  period  of  from  two  to  three 
weeks.     If,  however,  this  virus  is  passed  from  one 
rabbit  to  another,  its  virulence  gradually  increases 
until  the  incubation  period  decreases  to  six  days. 
At  this  point  it  is  called  fixed  virus  {virus  fixe), 
and  its   virulence   can   not  be   further  increased. 
Passage   through  the  cat,  fox  and  wolf  also  in- 
creases virulence.     On  the  other  hand,  by  passing 
it  repeatedly  through  the  monkey  (Pasteur),  the 
•    chicken  (Kraus)  or  the  dog  it  becomes  attenuated 
for  the  rabbit  and  virulence  may  be  lost  entirely. 
Low  viru-        Although  virus  fixe  represents  its  highest  degree 

Fixed  Vims,  of  virulcncc  for  rabbits,  there  is  good  reason  for 
believing  that  repeated  passage  through  the  rab- 
bit decreases  the  virulence  of  the  virus  for  man. 
In  other  words,  street  virus  is  more  infectious  for 
man  than  fixed  virus.  This  may  to  some  extent  ac- 
count for  the  success  of  the  Pasteur  treatment. 
Ferran,  indeed,  uses  unaltered  virus  fixe  for  the 
protective  inoculation  of  man. 

uistribntion  By  mcaus  of  iuoculatiou  experiments  the  virus 
the  n«dy.  may  be  •demonstrated  invariably  in  the  brain, 
spinal  cord,  and  usually  in  the  salivary  glands  and 
saliva  of  animals  which  have  died  of  the  disease. 
These  tissues  are  specifically  affected,  and  the  virus 
probably  proliferates  in  them.  By  one  or  another 
observer  its  presence  in  the  following  organs  and 


TRANSMISSION.  701 

excretions  has  been  demonstrated :  Suprarenal 
gland,  lachrymal  gland,  vitreous  humor,  urine,  tes- 
ticular secretion,  lymph,  milk,  in  the  peripheral 
nerves  and  cerbrospinal  fluid.  Marx  states  that 
it  has  not  been  found  in  the  liver,  spleen,  blood  and 
aqueous  humor.  Courmont  and  Nicolas  found  it, 
however,  in  the  aqueous  humor  of  rabbits  after 
death.  The  possibility  of  postmortem  invasion  of 
this  fluid  has  been  suggested.  It  has  been  found 
occasionally  in  human  saliva  during  life,  and  at 
the  site  of  the  wound  following  death  (Pace). 

Hydrophobia  is  transmitted  almost  exclusively  Means  of 
by  the  bites  of  infected  animals,  the  virus  being 
conveyed  in  the  saliva.  Accidental  inoculation  may 
occur  in  handling  infected  tissues.  The  virus  does 
not  penetrate  the  intact  skin,  and  it  is  customary  to 
consider  a  bite  as  harmless  unless  the  continuity 
of  the  skin  is  broken.  Experimentally,  infection 
has  been  caused  by  placing  the  virus  on  the  mu- 
cous membranes  of  the  conjunctiva,  nose  and 
mouth,  in  the  absence  of  discernible  lesions.  Pace 
mentions  a  man  who  contracted  the  disease  after 
his  rabid  dog  had  inserted  the  tip  of  its  tongue  in 
his  (the  patient's)  nose.  But  one  authentic  ex- 
ample of  transmission  from  man  to  man  is  found 
in  medical  literature.  This  occurred  through  kiss- 
ing or  biting,  during  coitus.  In  rare  instances  it 
seems  to  have  been  transmitted  from  the  mother 
to  the  fetus  in  rabbits. 

The  dog  is  the  most  common  carrier  of  hydro- 
phobia. In  some  countries  (Russia,  Hungary)  rabid 
wolves  cause  many  infections.  The  disease  has  been 
conveyed  by  the  bite  of  the  cat,  mouse  and  horse 
and  possibly  by  the  skunk  in  some  of  our  western 
states.     The  dog  is,  however,  the  natural  host  of 


702  I^U^ECTIOIS     A^D     IMMUNITY. 

the  parasite,  and  either  by  his  bite  or  by  experi- 
mental inoculation  practically  all  animals,  at  least 
mammalians,  may  be  infected. 

Incubation  The  incubation  period  in  animals  varies  from 
two  weeks  to  several  months.  In  man  it  varies 
between  twenty  and  sixty  days  usually,  but  may  be 
as  short  as  seven  or  ten  days,  or  as  long  as  twenty 
months  (rare).  In  children  it  is  shorter  than  in 
adults.  The  location  of  the  bite  is  also  of  impor- 
tance in  determining  the  length  of  incubation.  It 
is  shortest  following  wounds  of  the  head  and  neck, 
somewhat  longer  when  the  injury  is  in  the  hand  or 
arm,  and  still  longer  when  in  other  parts  of  the 
body.  The  degree  of  laceration  is  also  a  factor,  de- 
pending possibly  on  the  introduction  of  large;* 
quantities  of  virus,  and  on  larger  surfaces  for  its 
absorption.  The  bite  of  the  wolf  is  said  to  be  most 
virulent,  and  next  in  virulence  is  the  bite  of  the 
cat  and  dog. 

Not  all  who  are  bitten  by  rabid  animals  develop 
hydrophobia.  Correct  figures  on  this  point  are  dif- 
ficult to  obtain,  since  in  many  instances  the  ani- 
mals are  only  suspected  of  being  rabid.  According 
to  Hogyes,  from  15  to  16  per  cent,  of  those  who 
are  bitten  contract  hydrophobia.  The  percentage 
is  much  higher  following  bites  by  the  wolf.  The 
disease  is  invariably  fatal  to  man. 

The  symptoms  of  hydrophobia  in  man  differ  in 
no  essential  respects  from  those  seen  in  animals. 

DiagjrvoMis  The  immediate  determination  of  hydrophobia 
in  dogs  which  have  bitten  man  is  of  the  greatest 
importance.  In  many  instances  the  behavior  of  the 
animal  is  sufficiently  characteristic  to  justify  clin- 
ical diagnosis  of  the  disease.  The  disposition  of 
the  animal  changes  suddenly,  it  ceases  to  play,  eats 


in    Do^M. 


PATHOLOGY.  703 

various  indigestible  substances,  as  glass,  iron  and 
wood,  utters  pathognomonic  (?)  long-drawn-oat 
howls,  may  become  ferocious,  or,  on  the  other 
hand,  quiet  and  sullen.  At  autopsy  the  meninges 
and  nervous  tissue  are  congested  if  the  disease  is 
advanced,  and  the  indigestible  substances  men- 
tioned may  be  found  in  the  stomach,  although  the 
latter  finding  has  little  or  no  diagnostic  importance. 

A  number  of  histologic  changes  have  been  de-  So-caiieti 
scribed  as  characteristic.  Among  these  are  the  Le»fons. 
bodies  of  ISTegri,  described  above.  Eemlinger  at- 
taches a  great  deal  of  importance  to  them  as  a 
means  of  diagnosis.  Babes  describes  perivascular 
nodules  of  lymphoid  cells  (Wutknotchen)  in  the 
medulla  and  cord.  The  lesion  of  Van  Gehuchten 
consists  of  a  proliferation  of  the  endothelial  cells 
(neuronophages)  surrounding  the  ganglionic  cells, 
the  latter  at  the  same  time  undergoing  atrophic 
and  degenerative  changes.  This  change  is  most 
marked  in  the  cervical  ganglia.  One  group  of  ob- 
servers finds  these  lesions  constant  in  animals 
which  have  died  of  hydrophobia,  but  they  may  be 
absent  if  the  animal  is  killed  during  the  course  of 
the  disease;  hence  their  absence  does  not  exclude 
the  diagnosis  of  hydrophobia.  Others  have  found 
similar  changes  in  other  diseases.  Metchnikoff, 
it  will  be  remembered,  observed  the  destruction  of 
ganglionic  cells,  by  neuronophages  in  aged  dogs 
(page  309). 

We  are  hardly  able  at  present  to  consider  these 
changes  as  pathognomonic.  Particularly  in  early 
stages  of  the  disease  they  may  be  absent.  The  bite 
of  a  rabid  dog  is  infectious  in  from  two  to  four 
days  in  advance  of  the  development  of  symptoms, 
and  autopsy  performed   at  this  time  may  show 


N 


704  INFECTION     AND     IMMUNITY. 

neither  gross  nor  microscopic  changes  which  are 
characteristic. 
Extension  A  great  deal  of  experimental  work  which  can  not 
Nerves!  bc  given  in  detail  shows  conclusively  that  the  virus 
is  conveyed  to  the  central  nervous  system  by  means 
of  the  peripheral  nerves.  The  conditions  then  are 
similar  to  those  in  tetanus  with  this  exception:  In 
hydrophobia  the  living  virus  reaches  the  central 
nervous  system,  whereas  in  tetanus  the  bacilli  re- 
main at  the  site  of  the  wound.  This  condition  ex- 
plains the  shorter  incubation  period  in  hydropho- 
bia, as  in  tetanus,  when  the  infection  atrium  is 
near  the  central  nervous  system  (e.  g.,  face).  When 
the  infection  is  introduced  into  any  particular 
part  of  the  body  surface,  the  virus  is  first  demon- 
strable in  the  corresponding  segment  of  the  cen- 
tral nervous  system.  Although  transmission  by 
the  nerves  is  the  rule,  infection  may  be  accom- 
plished in  rabbits  by  intravascular  injection.  On 
the  whole,  however,  infection  is  closely  associated 
with  the  wounding  of  nerves.  It  has  indeed 
been  shown  that  if  wounding  of  nerves  is  entirely 
avoided,  as  in  intraperitoneal  injections  into  rab- 
bits (Marx)  the  full  virulent  nervous  tissue  may 
be  used  for  immunization.  A  single  injection  of  a 
large  quantity  brought  about  immunity  in  twelve 
days. 

The  muzzling  of  dogs  is  a  general  prophylactic 
measure,  which  should  be  enforced  in  communities 
in  which  hydrophobia  is  known  to  occur.  No  mat- 
ter how  thoroughly  the  cauterization  and  antisep- 
tic treatment  of  wounds  is  carried  out  it  can  in  no 
case  be  depended  on  to  destroy  the  virus.  Even 
within  five  minutes  the  virus  may  be  carried  to  a 
point  which  is  beyond  the  reach  of  the  cautery.    In 


PASTEUR     TREATMENT. 


706 


spite  of  this  fact,  however,  cauterization  should 
not  be  neglected,  even  when  the  Pasteur  treatment 
can  be  instituted  at  once.  The  greater  the  quantity 
of  virus  introduced  by  the  bite  the  shorter  will  be 
the  incubation  period,  and  there  is  good  reason  to 
believe  that  cauterization  (actual  cautery)  prop- 
erly carried  out  destroys  a  sufficient  amount  of 
virus  to  prolong  the  incubation  period.  A  long 
incubation  period  is  greatly  in  favor  of  the  success 
of  the  Pasteur  treatment. 

In  communities  in  which  hydrophobia  is  known 
to  be  endemic,  in  all  cases  of  dog  bite  accompanied 
by  penetration  of  the  skin,  the  patient  should  re- 
ceive the  Pasteur  treatment. 

Pasteur's  first  protective  inoculations  were  car- 
ried out  with  virus  which  had  been  attenuated  by 
passage  through  the  monkey.  The  virus  fixe  ob- 
tained from  the  rabbit,  as  described  above,  was 
soon  substituted  for  that  of  the  monkey.  In  order 
that  an  antirabic  institute  may  continuously  have 
on  hand  a  sufficient  amount  of  vaccine,  it  is  neces- 
sary to  inoculate  two  or  three  rabbits  daily.  For 
this  purpose  an  emulsion  of  the  medulla  of  a  rab- 
bit which  has  died  of  hydrophobia  is  inoculated  be- 
neath the  dura  mater.  A  short  time  before  the 
animals  would  die  of  the  disease,  they  are  killed 
by  bleeding,  and  the  spinal  cords  removed  with  all 
possible  precautions  for  asepsis.  Each  cord  is  cut 
into  two  parts  and  each  part  suspended  in  a  prop- 
erly constructed  jar  which  contains  solid  potas- 
sium hydrate.  After  the  jar  is  sealed  desiccation 
is  allowed  to  proceed  for  fourteen  days,  at  the  end 
of  which  time  the  infectiousness  of  the  tissue  has 
so  decreased  that  it  is  suitable  for  the  first  injec- 
tion.    The  vaccine  should  be  free  from  bacteria. 


Preparation 
of  Virus  for 
Pasteur 
Treatment. 


706  INFECTION     AND     IMMUNITY. 

According  to  Haryey  and  McKendrick,  the  degree 
of  infectivity  of  dried  rabic  yirus  is  a  "function 
of  the  loss  of  weight  in  water  caused  by  the  dry- 
ing/' 
Technic  of       As    is    wcll    known,    the    Pasteur    prophylactic 

Treatment  .  . 

treatment  consists  of  the  subcutaneous  injection 
on  successive  days,  of  suitable  quantities  of  virus 
fixe,  prepared  as  described  above^  beginning  with 
the  cord  which  has  been  desiccated  for  fourteen 
days  and  gradually  using  fresher  cords  until  viru- 
lent virus  has  been  inoculated.  The  vaccine  is  pre- 
pared for  use  by  emulsifying  one  centimeter  of  a 
cord  in  5  c.c.  of  salt  solution  or  some  "artificial 
serum/'  and  in  a  single  treatment  from  1  to  3  c.c. 
of  this  emulsion  is  injected,  usually  into  the  sub- 
cutaneous tissue  of  the  anterior  abdominal  wall. 
In  this  region  there  is  less  likelihood  of  injuring 
large  nerves,  and  local  complications,  which,  how- 
ever, occur  rarely,  are  of  less  consequence. 

The  rapidity  with  which  one  should  pass  from 
the  fourteen-day  cord  to  fresh  virus  depends  on  the 
urgency  of  the  case.  When  there  is  good  reason  to 
suspect  a  short  incubation  period,  or  when  some 
days  have  followed  the  bite  an  "intensive"  treat- 
ment should  be  used ;  in  other  cases  the  progression 
may  be  slower.  The  following  conditions  augur 
a  short  incubation  period :  Bites  of  children,  who 
are  more  susceptible  than  adults,  and  in  whom 
the  injuries  usually  are  on  the  face;  bites  on  the 
face  and  neck  in  all  cases;  lacerated  wounds  in 
which  there  is  a  larger  surface  for  absorption  of 
the  virus.  The  influence  which  proper  cauteriza- 
tion exerts  on  the  incubation  period  was  mentioned 
above. 


PASTEUR     TREATMENT.  707 

The  table  on  page  708,  taken  from  Marx,  illus- 
trates a  "light"  and  an  '^^intensive"  treatment. 

This  scheme  is  variously  modified  in  different 
institutes,  especially  in  the  direction  of  a  more 
rapid  progression  to  virulent  material. 

Other  methods  of  attenuation  are  also  used,  as  S,*^**^     . 

.  Means  of 

the  following:  Heating  emulsions  of  fresh  virus  Attennation. 
at  58°  C.  for  different  lengths  of  time,  or  at  dif- 
ferent temperatures  (80°  to  30°  C.)  for  ten  min- 
utes (Babes-Puscari)  ;  digestion  of  virus  with  nat- 
ural or  artificial  gastric  juice  (Tizzoni  and  Cen- 
tanni)  ;  the  use  of  fresh  but  very  dilute  virus 
(Hogyes).  Ferran,  in  Barcelona,  inoculates  man 
with  the  fresh  unaltered  virus  fixe,  and  in  nearly 
2,000  cases  but  two  cases  of  hydrophobia  devel- 
oped. This  indicates  clearly  the  low  infectious- 
ness of  virus  fixe  for  man. 

The  tendency  at  present  is  toward  the  use  of 
fresh  rabic  virus  for  the  prophylactic  treatment  of 
hydrophobia.  This  is  the  method  of  Hogyes,  and 
also  of  Ferran.  Hogyes'  first  injection  consists  of 
3  c.c.  of  a  1  to  10,000  or  1  to  8,000  dilution  of 
the  fresh  rabic  cord,  and  gradually  within  the  next 
fourteen  days  the  concentration  is  increased  until 
1  c.c.  of  a  dilution  of  1  to  100  is  given. 

In  order  to  obtain  a  basis  of  comparison  for 
the  different  methods  of  treatment  Harvey  and 
McKendrick  have  proposed  an  arbitrary  unit  of 
standardization  for  rabic  virus.  For  this  purpose 
they  agreed  to  consider  that  0.2  c.c.  of  a  1  per 
cent,  emulsion  of  the  fresh  virus  fixe  contains 
1,000  units.  From  this  it  follows  that  0.2  c.c. 
of  a  1  to  1,000  emulsion  would  contain  100  units, 
and  0.2  c.c.  of  a  1  to  1,000  dilution,  10  units. 


708 


INFECTION     AND     IMMUNITY. 


The  first  dose  in  the  Hogyes  method  according  to 
this  scale  represents  150  units.  Naturally  those 
methods  in  which  dried  virus  is  used  for  at  least 
part  of  the  treatment  can  not  be  expressed  in  units 
until  the  infective  value  of  the  cords  dried  for  dif- 
ferent periods  is  determined.     This  was  investi- 


Light. 

Intensive. 

Day  of 

Age  of 

Amount  of 

Day  of 

Age  of 

Amount  of 

Treat- 

Dried Cord 

Emulsion 

Treat- 

Dried Cord 

Emulsion 

ment. 

in  Days. 
1X3 

Injected. 
3 

ment. 

in  Days. 

Injected. 

1 

ru 

3 

3 

1 

Il3 

3 

2 

U2 

hi 

3 

1l2 

3 

3 

111 

3 

3 

i  10 

(    9 

3 

no 

3 

3 

9 

8 
7 

3 

4 

5    8 

/    7 

3 
3 

3 
3 

5 

'    6 

;  6 

2 

9 

3 

5    6 

i  6 

2 
2 

6 

5 

2 

4 

5 

2 

7 

5 

2 

5 

5 

2 

8 

4 

2 

6 

4 

2 

9 

3 

1 

7 

3 

1 

10 

5 

2 

8 

4 

2 

11 

5 

2 

9 

3 

1 

12 

4 

2 

10 

5 

2 

13 

4 

2 

11 

5 

2 

U 

3 

2 

12 

4 

0 

15 

3 

2 

13 

4 

2 

16 

5 

2 

14 

3 

9 

17 

4 

2 

15 

3 

2 

18 

3 

2 

16 

5 

2 

17 

4 

2 

18 

3 

2 

19 

5 

2 

20 

4 

2 

21 

3 

2 

gated  by  Harvey  and  McKendrick  and  their  con- 
clusions were  as  follows:  "(1)  Emulsion  of  the 
nine-day  cord  is  little  if  at  all  infective  in  a  dose 
of  0.2  c.c.  of  a  1  in  5  emulsion.  (2)  Emulsion 
of  five-day  cord  is  infective  in  minimal  time  in  a 
dose  of  0.2  c.c.  of  a  1  in  100  emulsion,  but  be- 
come less  so  or  not  at  all  in  a  dose  of  0.2  c.c.  of 


PASTEUR     TREATMENT.  709 

a  1  in  200  emulsion.  (3)  In  the  same  way  the 
M.  I.  D.  (minimum  infective  dose)  for  an  emul- 
sion of  three-day  cord  is  0.2  c.c.  of  a  1  in  200 
'emulsion.  (4)  The  M.  I.  D.  of  two-day  cord  is 
not  greater  than  0.2  c.c.  of  a  1  in  1,000  emulsion 
and  probably  not  less  than  0.2  c.c.  of  a  1  in  2,000 
emulsion.  (5)  The  M.  I.  D.  of  one-day  cord  is 
not  greater  than  0.2  c.c.  of  a  1  in  4,000  emulsion 
and  almost  certainly  not  less  than  0.2  c.c  of  a 
1  in  8,000  emulsion  (the  lower  accepted  limit  of 
fresh  material).  (6)  Fresh  material  is  infective 
(M.  I.  D.)  in  a  dose  of  0.2  c.c.  of  a  1  in  8,000 
dilution  and  may  be  so  in  considerably  higher 
dilutions  even  up  to  1  in  40,000,  but  with  such 
high  dilutions  the  experimental  errors  become  so 
great  as  to  preclude  any  more  exact  fixation  of 
the  M.  I.  D." 

Although  these  results  are  not  mathematically 
exact,  it  is  probable  that  they  may  be  used  as  a 
working  basis,  and  from  them  it  is  possible  to 
calculate  the  number  of  units  in  a  given  amount 
of  rabic  cord  dried  for  different  periods.  Harvey 
and  McKendrick  estimate  that  in  both  the  Pas- 
teurian  method  and  that  of  Hogyes  little  more 
than  25,000  units  are  administered  during  the 
course  of  treatment. 

It  seems  unnecessary  at  this  date  to  quote  sta- 
tistics to  show  the  value  of  the  Pasteur  treatment. 
Observations  indicate  that  immunity  is  not  fully 
established  until  about  fourteen  days  after  the 
completion  of  the  treatment,  and  in  a  certain  num- 
ber of  cases  the  disease  develops  before  this  time 
has  passed.  The  number  of  deaths  after  this  pe- 
riod is  exceedingly  small  and  has  grown  less  with 


710  INFECTION     AND     IMMUNITY. 

improved  technic.  In  1886  the  number  of  deaths 
which  occurred  after  fifteen  days  had  passed 
amounted  to  0.94  per  cent.;  in  1902  to  0.18  per 
cent. 

immunitF  The  immunity  established  by  the  Pasteur  treat- 
properties.  mcut  is,  in  all  probability,  antimicrobic  in  nature. 
The  serum  of  both  man  and  animals,  after  immun- 
ization, is  able  to  destroy  the  infectiousness  of  rabic 
nervous  tissue,  i.  e.,  the  serum  is  rabicidal  (Babes 
and  Lepp,  1889).  The  technic  of  Kraus  and 
his  co-laborers  is  well  adapted  to  show  the  rabi- 
cidal properties  of  the  immune  serum.  Eabid  ner- 
vous tissue  is  made  into  an  emulsion  witli  salt 
solution  in  a  dilution  of  1  to  100,  and  then  filtered 
through  paper  to  remove  coarse  particles  of  tissue. 
To  quantities  of  0.5  to  1.0  c.c.  of  this  emulsion 
varying  amounts  of  fresh  immune  serum  are  added, 
and  after  eighteen  hours'  contact  the  mixtures  are 
injected  into  rabbits  to  determine  the  degree  of 
infectiousness.  Small  quantities  of  rabicidal  sub- 
stance may  be  detected  in  this  way. 

Natural  resistance  to  hydrophobia  does  not  go 
hand  in  hand  with  the  antirabic  power  of  an  ani- 
mal's serum.  Old  pigeons,  for  example,  develop  the 
disease  following  intracerebral  injection  of  the 
virus,  although  their  serum  is  not  rabicidal. 

Babes  and  Lepp  also  showed  that  the  immune 
serum  has  protective  powers  which  are  analogous 
in  their  efficiency  with  those  of  bactericidal  serums. 
Babes  advocates  and  practices  the  mixed  method 
of  immunization  in  severe  cases,  immune  serum  be- 
ing injected  in  addition  to  the  virus.  The  serum 
has  little  or  no  curative  value. 


YELLOW    FEVER.  711 


II.     YELLOW  FEVER. 


Yellow  fever  is  peculiarly  an  American  disease, 
and  it  has  reached  other  continents  (e.  g.,  Spain) 
only  in  accidental  ways  and  for  brief  periods.  It 
is  possibly  endemic  in  certain  portions  of  West 
Africa  (Sierra  Leone),  to  which  it  was  probably 
carried  from  the  Antilles  (Scheube).  Schenbe 
regards  the  Antilles  as  the  birthplace  of  yellow 
fever.  Knowledge  of  it  extends  only  to  the  middle 
of  the  seventeenth  century,  at  which  time  it 
surely  existed  in  the  West  Indies.  The  dis- 
ease has  on  several  occasions  been  carried  to 
Spain  by  vessels  returning  from  Cuban  ports. 
Until  very  recent  times  it  was  endemic  in 
Cuba,  especially  Havana,  and  in  Vera  Cruz 
and  other  Spanish- American  ports  it  has  prevailed 
extensively.  From  such  points  extension  frequent- 
ly takes  place  into  adjacent  tropical  or  subtropical 
regions,  or  even  into  temperate  localities  during 
the  summer  months.  In  the  latter  part  of  the 
eighteenth  century  Philadelphia  suffered  very  se- 
verely. Baltimore  was  attacked  similarly  and  Bos- 
ton to  a  less  degree.  Other  northern  ports,  e.  g., 
New  York,  have  experienced  attacks  of  limited 
duration,  the  disease,  presumably,  being  intro- 
duced by  means  of  infected  ships. 

In  addition  to  our  southern  coasts  and  that  of 
Mexico,  the  Atlantic  coast  of  South  America  has 
been  infected  as  far  south  as  Buenos  Ayres,  and 
likewise  the  western  coast  of  Mexico  and  Peru.  In 
the  eighteenth  century  the  coast  of  Spain  and 
Portugal  suffered  severely,  but  since  that  time 
only  minor  epidemics  have  occurred  in  these  coun- 
tries. Epidemics  frequently  have  appeared  on 
ships  after  they  had  left  infected  ports. 


712 


INFECTION     AND     IMMUNITY. 


Bacillus 
Icteroides. 


The  Mosqnito 
Theory. 


The  Southern  States  were  invaded  repeatedly  in 
the  last  decade  of  the  eighteenth  century,  in  1803, 
1805,  1853,  1867,  1873,  1878,  1905,  and  in  lesser 
degrees  at  other  times,  in  all  ninety-six  times.  The 
severest  epidemics  were  those  of  1853  and  1878. 

The  many  microbes  which  have  been  cited  as  the 
cause  of  yellow  fever  need  not  be  described.  The 
Bacillus  ideroides  of  Sanarelli,  which  had  at- 
tained more  prominence  than  any  other,  was  shown 
by  Sternberg,  by  Eeed  and  Carroll  and  by  the  more 
recent  work  on  the  mosquito  theor}^,  to  bear  no 
causal  relationship  to  the  disease.  According  to 
Eeed  and  Carroll  it  is  identical  with  the  hog-chol- 
era bacillus. 

The  monumental  work  of  Eeed,  Carroll,  Agra- 
monte  and  Lazear  (1900),  the  last  of  whom  lost 
his  life  from  yellow  fever,  has  made  it  possible 
to  replace  accurate  knowledge  of  the  epidemiolog}* 
and  prophylaxis  of  yellow  fever  and,  to  a  certain 
extent,  of  its  etiology,  for  many  incorrect  ideas 
which  had  prevailed  up  to  that  time. 

The  conception  that  yellow  fever  is  transferred 
from  one  person  to  another  by  mosquitoes  was 
first  advanced  positively  by  Carlos  Finlay,  a 
Cuban  physician,  in  1881,  although  several  Ameri- 
can physicians  had  long  before  noted  the  preva- 
lence of  mosquitoes  during  yellow  fever  outbreaks 
(Eush,  1793;  Weightman,  1839 ;  Wood,  1853; 
Barton,  1853).  Finlay  reported  the  transmission 
of  the  disease,  experimentally,  by  the  bites  of  mos- 
quitoes which  had  fed  on  yellow-fever  patients, 
and  stated  that  light  attacks  which  followed  the 
bites  resulted  in  the  establishment  of  immunity. 
The  subsequent  observations  of  Eeed  and  his  co- 
workers indicate,  however,  that  Finlay's  technic 


STEGOMYIA     FASCIATA. 


713 


Stegromyia 
Fasciata. 


was  such  that  he  could  not  possibly  have  produced 
experimental  fever,  and  that  the  development  of 
the  disease  in  his  subjects  was  purely  a  coincidence. 
The  reason  for  this  will  appear  below. 

Having  satisfied  themselves  that  Bacillus  icte-  Tiie  "Work  of 
roides  is  but  an  accidental  organism  in  yellow  Etc.f  with***** 
fever,  and  that  it  is  found  under  normal  condi- 
tions as  well,  Eeed  and  his  associates  began  work 
on  the  mosquito  hypothesis  of  Finlay.  The  first 
positive  result  was  obtained  in  the  case  of  Dr.  Car- 
roll. Carroll  "was  bitten  at  2  p.  m.,  Aug.  27,  1900, 
by  Stegomyia  fasciata.  This  particular  mosquito 
had  bitten  a  severe  case  of  yellow  fever  on  the 
second  day  of  the  disease,  twelve  days  before;  a 
mild  case  of  yellow  fever  on  the  first  day  of  the 
attack,  six  days  preceding;  a  severe  case  of  yellow 
fever  on  the  second  day  of  the  attack,  four  days 
before ;  a.  mild  case  of  yellow  fever  on  the  second 
day  of  attack,  two  days  before  inoculation."  After 
an  incubation  period  of  three  days,  Carroll  devel- 
oped typical  and  severe  yellow  fever,  from  which 
he  recovered.  A  similar  result  in  one  other  case 
was  reported  at  this  time,  and  later  Camp  Lazear, 
with  mosquito-proof  houses,  was  established  for  the 
continuation  of  the  study.  The  experiments  of 
Reed  and  his  co-workers,  and  confirmatory  work  by 
Guiteras  and  the  French  commission,  can  not  be 
described  in  this  place.  We  may  feel  sure,  how- 
ever, that  with  all  the  conditions  of  experimenta-  J^^f'^^-J^icii 
tion  under  absolute  control  the  following  points  Have  Been 
have  been  determined  with  scientific  certainty:  1. 
Yellow  fever  may  be  transferred  from  a  patient  to 
a  non-immune  by  the  bite  of  a  mosquito — Stego- 
myia fasciata — which  has  previously  fed  on  a 
3'ellow-fever  patient.     2.  In  order  that  the  mos- 


714  INFECTION     AND     IMMUNITY. 

quito  become  infected  it  is  necessary  for  him  to 
feed  on  yellow-fever  blood  within  the  first  few 
days  (three  days)  of  the  fever.  3.  The  mosquito 
can  not  transfer  yellow  fever  directly  and  imme- 
diately from  the  patient  to  a  non-immune,  but  it 
is  necessary  for  a  period  of  not  less  than  twelve 
days  to  elapse  before  he  becomes  infectious.  When 
this  time  has  been  reached  the  insect  continues  in- 
fectious for  at  least  fifty-seven  days  and  probably 
throughout  his  life.  4.  Yellow  fever  can  not  be 
transferred  by  ^^fomites."  5.  The  subcutaneous  in- 
jection of  yellow  fever  blood  into  a  non-immune 
produces  yellow  fever,  hence  the  infecting  agent 
exists  in  the  circulation.  6.  The  serum  of  a  yel- 
low fever  patient,  after  being  diluted  and  filtered 
through  a  Berkefeld  filter  (Eeed  and  Carroll)  or 
Chamberland  B  porcelain  filter  (Rosenau,  Parker, 
Francis  and  Beyer)  is  infectious,  hence  the  in- 
fecting agent  at  some  stage  of  its  development  is 
very  minute,  possibly  ultramicroscopic.  7.  "An 
attack  of  yellow  fever  produced  by  the  bite  of  a 
mosquito  confers  immunity  against  the  subsequent 
injection  of  the  blood  of  an  individual  suffering 
from  the  non-experimental  form  of  this  disease" 
(Reed,  Carroll  and  Agramonte).  8,  The  period  of 
incubation  usually  is  three  days,  but  may  vary 
within  the  limits  of  from  two  to  six  days.  9.  "A 
house  may  be  said  to  be  infected  with  yellow  fever 
only  when  there  are  present  within  its  walls  con- 
taminated mosquitoes  capable  of  conveying  the 
parasite  of  the  disease.'^  10.  "The  spread  of  yel- 
low fever  can  be  most  effectually  controlled  by 
measures  directed  to  the  destruction  of  mosquitoes 
and  the  protection  of  the  sick  against  the  bites  of 
these  insects."    11.  jSTo  mosquito  other  than  Stego- 


STEGOMYIA     FASGIATA.  715 

mijia  fasciata  has  been  found  capable  of  transmit- 
ting the  diseasCj  and  analogies  suggest  the  proba- 
bility that  no  other  insect  is  concerned. 

These  discoveries  explain  many  facts  in  rela-  Epidemiology 
tion  to  yellow  fever  which  had  been  obscure  hither-  SJyia. 
to.  For  example,  yellow  fever  is  a  tropical  and 
subtropical  disease  only  because  Stegomyia  fas- 
ciata breeds  in  tropical  and  subtropical  climates. 
The  disease  is  found  in  low,  moist  localities  rather 
than  in  the  high  and  dry,  because  the  mosquito  in- 
habits the  former  and  not  the  latter.  Yellow 
fever  dies  out  with  the  first  severe  frost  or  on  the 
advent  of  cool  weather  because  these  conditions 
either  kill  the  mosquito  or  cause  him  to  hibernate. 
The  advent  of  an  initial  case  of  yellow  fever  in  a 
suitable  region  is  followed  by  the  appearance  of  the 
disease  in  epidemic  form  only  after  a  period  of  two 
or  three  weeks,  because  the  mosquito  first  becomes 
infectious  in  about  two  weeks  after  it  has  fed  on 
yellow  fever  blood;  this  may  correspond  with  a 
certain  stage  of  development  of  the  as  j-et  unrecog- 
nized parasite.  The  observation  often  made  that 
yellow  fever,  like  malaria,  is  not  contagious  in  the 
ordinary  sense,  in  spite  of  its  rapid  extension,  is 
readily  understood,  as  is  the  irregular  method  in 
which  the  disease  spreads.  It  is  now  clear  why  the 
disinfection  of  fomites  has  never  been  able  to 
check  the  advance  of  an  epidemic,  and  why  the 
ordinary  quarantine  measures  which  did  not  take 
the  mosquito  into  consideration  were  not  effective 
in  keeping  the  disease  out  of  a  favorable  port ;  and 
by  a  favorable  port  is  meant  one  which  can  harbor 
Stegomyia  fasciata.  These  discoveries  also  ex- 
plain how  yellow  fever  could  be  stamped  out  of 
Havana,  Texas  and  New  Orleans  by  prophylactic, 


716  INFECTION     AND     IMMUNITY. 

hygienic  and  quarantine  measures,  which  had  a^ 
their  objects  the  destruction  of  the  mosquito  and 
its  breeding  places  and  prevention  of  the  infection 
of  the  mosquitoes  by  suitably  screening  the  pa- 
tients. 
Distribution       j^  is  thus  sccn  that  the  epidemic  occurrence  of 

of  StegroniT'ia.  ^  . 

yellow  fever  is  strictly  associated  with  the  distribu- 
tion of  Stegomyia  fasciata.  Howard,  in  Bulletin 
No.  46  of  the  Public  Health  Eeports,  gives  this 
distribution  as  known  on  Sept.  10,  1905,  and  pub- 
lishes a  map  showing  the  region  which  the  insect 
may  be  expected  to  inhabit. 

Stegomyia  fasciata  has   been   found   in   the   following 
localities  in  the  United  States   (Howard)  : 

Virginia:    Virginia  Beach,  Norfolk,  Lynchburg,  Dan- 
ville,   Richmond.      Kentucky:     Lexington,    Middlesboro, 
Louisville,     Richmond.       Illinois:      Cairo.       Tennessee: 
Nashville,  Knoxville,  Clarksville,  Chattanooga,  Memphis, 
Columbia,    Decherd,    Athens,    Bristol.     Arkansas:     Hot 
Springs,    Helena.     Louisiana:    Ruddock,    New    Orleans, 
Baton     Rouge,     Napoleonville,     Covington,     Hammond, 
Shreveport,  Franklin,  Morgan  City,  New  Iberia,  Patter- 
son.   Mississippi:    Pass  Christian,  Summit,  Quarantine 
Station,  Vicksburg,  Clarksdale,  Tutwiler,  Belzoni,  Holly 
Springs,  Jackson,  Wonona,  West  Point,  Tupelo,  Corinth 
Agricultural  College,  Biloxi.   Alabama:  Mobile,  Decatur 
Auburn,   Tuscumbia,   Huntsville,  Yazoo   City.    Georgia 
Atlanta,      Pelham,      Augusta,      Savannah,      Brunswick 
Florida:     Barrancas,     Key     West.     Texas:     Galveston 
Houston,   Victoria,    San    Diego,    Tyler,   Laredo,    Austin 
San   Antonio,    Corsicana,    Brownsville,    Alice,    Colorado 
Dallas,  Paris,  Edna,  Fort  Bliss    (El  Paso),  Fort  Ring 
gold    (Rio  Grande-Ludlow).    South  Carolina:    Charles 
ton,    Columbia,   Fort   Fremont,    Sullivan's   Island.    Ari 
zona:    Nogales.    Maryland:    Baltimore   (Carter) — breed 
ing  in  fresh  water  on  fruit  wharf.  North  Carolina:  Beau 
fort,  Winston,  Raleigh,  Greensboro,  Charlotte,  Salisbury 
Indiana:    JeflFersonville.    Missouri:    St.  Louis. 


8TEG0MYIA     FA8CIATA.  717 

Eeed  and  Carroll  found  the  larvae  of  stegorayia  Breeding 

1  1  /^\     •       J-  j_i     J.    PlaceH  and 

"(1)  m  ram-water  barrels;    (2)  m  tm  cans  that  Life  cycic. 
had  been  used  for  removing  excreta  and  which 
still  contained  a  small  amount  of  fecal  matter; 

(3)  in   sagging   gutters   containing   rain   water; 

(4)  in  cesspools;  (5)  in  tin  cans  placed  about 
table  legs  to  prevent  the  inroads  of  red  ants;  (6) 
in  the  collection  of  water  at  the  base  of  the  leaves 
of  the  agave  americana;  (7)  in  one  end  of  a 
horse  trough  that  was  in  daily  use."  These  in- 
stances are  cited  to  show  the  general  character  of 
the  places  in  which  the  eggs  and  larvae  of  stegomyia 
may  be  found.  The  eggs  are  deposited  during  the 
night,  in  about  seven  days  after  the  ingestion  of 
blood,  and  "in  pairs,  in  groups  of  three  or  more 
or  singly,"  to  the  number  of  forty-seven  on  the 
average  (Eeed  and  Carroll).  The  eggs  are  very 
resistant  to  drying  and  extreme  cold  ( — 17°  C). 
^Yith  a  favoraljle  temperature  they  hatch  in  from 
three  to  seven  days ;  the  larval  stage  lasts  for  seven 
days,  'the  pupal  two  days,  the  total  cycle  being 
completed  in  about  twelve  days.  As  in  the  case  of 
anopheles,  only  the  female  stegomyia  sucks  blood. 
The  insect  prefers  the  hours  from  3  p.  m.  to  9  a. 
m.  for  feeding,  but  is  most  active  from  4  p.  m. 
to  midnight.  "In  captivity  the  hungry  impreg- 
nated female  will  bite  at  any  hour  of  the  day  or 
night."  In  a  state  of  freedom  it  will  not  bite  a  Biting? ^ 
second  time  for  from  five  to  seven  days.  It  ap- 
pears not  to  bite  when  the  temperature  is  lower 

than  62°  F.,  another  factor  in  the  subsidence 
of  yellow  fever  with  the  advent  of  cool  weather. 
For  further  details  concerning  the  morphology, 
biology  and  habits  of  stegomyia  consult  Howard 
on  "The  Mosquito" ;  Eeed  and  Carroll,  "The  Pre- 


718  INFECTION     AND     IMMUNITY. 

vention  of  Yellow  Fever,"  Medical  Record,  Oct. 
26,   1901;    Parker,  Beyer   and   Pothier,  "Report 
of  Working  Party  No.  1,"  Yellow  Fever  Institute 
Bulletin  No.  13,  1903,  Washington. 
Importation       Yellow  fever  cases  and  stegomyia  work  together 
y     lips.  .^  ^^^^  extension  of  the  disease  just  as  malarial 
cases  and  anopheles  do  in  the  extension  of  ma- 
laria;   for  the  principles  involved  the  chapter  on 
malaria  may  be  consulted.     Of  particular  interest 
is  the  importation  of  the  disease  by  means  of  ships, 
since  the  invasion  of  the  United  States  usually 
comes  about  in  this  way.     It  is  frequently  stated 
that  ships  lying  one-half  mile  from  shore  are  safe 
from  yellow  fever;   Grubbs,  however,  believes  that 
stegomyia  may  reach  vessels  lying  within  fifteen 
miles  of  the  shore  if  the  wind  is  favorable.     The 
insect  readily  boards  a  vessel  lying  in  an  infected 
port  and  may  remain  there  at  least  during  a  sev- 
enteen days'  voyage.    It  may  also  breed  in  suitable 
barrels  or  tanks  of  water  on  the  ship.    Under  these 
conditions  it  is  readily  understood  how  a   ship, 
leaving  a  harbor  with  a  healthy  crew,  may  be  at- 
tacked by  yellow  fever  a  few  days  after  leaving 
port;   and  how  any  quarantine  measure  at  a  new 
port  which  does  not  involve  the  destruction  of  the 
mosquitoes  on  the  boat  and  the  protection  of  the 
patients  from  the  bites  of  mosquitoes  is  inadequate. 
Resistance       As  statcd,  the  nature  of  the  virus  is  unknown. 
of  \iras.  j^^   fiiterability   was   mentioned.     A  temperature 
of   55°    C.   for    ten    minutes   renders   innocuous 
the  defibrinated  blood  of  the  infected ;  according  to 
the    French    Commission    (Marchoux,    Salimbeni 
and  Simond)  the  virus  is  destroyed  in  five  minutes 
at  this  temperature.     The  latter  also  found  that 
defibrinated  blood  when  sealed  under  vaselin  re- 
tained its  virulence  for  five,  but  not  for  eight  days. 


PROPHYLAXIS. 


719 


The  toxic  substance  appears  to  have  a  strong  af- 
finity for  the  parenchymatous  organs,  particularly 
the  liver  and  kidney. 

The  essential  principles  of  prophylaxis  have  Propiiyiaxi*. 
been  alluded  to :  1,  the  destruction  of  breeding 
places  for  the  mosquito  as  described  in  the  section 
on  malaria;  2,  the  isolation  of  patients,  screened, 
to  exclude  mosquitoes;  3,  the  destruction  of  mos- 
quitoes found  in  infected  houses  or  ships;  4,  the 
individual  factor  of  avoiding  the  bites  of  mos- 
quitoes, which  involves  the  screening  of  houses, 
and  individual  care.  One  may  go  about  more 
safely  in  the  middle  of  the  day  than  before  9  a. 
m.  and  after  3  p.  m.  For  the  disinfection  of 
houses,  i.  e.,  for  the  destruction  of  mosquitoes,  two 
pounds  of  tobacco  or  two  pounds  of  pyrethrum 
powder  per  1,000  cubic  feet  of  space  may  be  burned 
after  the  rooms  are  sealed.  When  smaller  quan- 
tities are  used  the  insects  may  be  only  stupified, 
and  should  be  collected  and  burned  (Rosenau,  Par- 
ker, Beyer  and  Pothier).  Sulphur  dioxid  is  highly 
efficient,  but  formaldehyd  is  valueless  as  an  in- 
secticide (Rosenau). 

The  negro  is  less  susceptible  to  yellow,  fever  than  sascepti- 
the  white  man  and  in  him  the  mortality  is  lower. 
Among  the  natives  the  mortality  is  from  7  to  10 
per  cent.,  among  the  whites  from  20  to  80  per  cent. 
(Scheube).  The  statement  that  Caucasians  may 
become  "acclimated"  so  that  they  are  less  suscep- 
tible needs  additional  investigation.  It  seems  im- 
possible that  acclimatization  could  mean  anything 
else  than  active  immunization.  Children  and  the 
aged  are  attacked  less  frequently  than  those  be- 
tween the  ages  of  ten  and  thirty. 

An  attack  of  yellow  fever,  whether  experimental 
or  natural,  confers  immunity  of  long  or  lasting  du- 


720  INFECTION     AND     IMMUNITY. 

Immunity  ration.  According  to  the  French  Commission,  a 
p?opert'iis*  certain  degree  of  immunity  could  be  conferred  by 
the  injection  of  infected  serum  which  had  been 
heated  to  55°  C.  for  five  minutes,  or  of  defibri- 
nated  blood  which  had  been  kept  under  vaselin 
oil  at  room  temperature  for  eight  days.  They  also 
claimed  that  the  serum  of  convalescents  has  pro- 
phylactic and  curative  properties  to  a  certain  de- 
gree. 

HI.    ^'spotted  fever''  of  the  rocky  mountain 

STATES. 

In  the  valley  of  the  Bitter  Eoot  Eiver  of  Mon- 
tana, and  in  certain  sections  of  Idaho,  Wyoming 
and  Washington  an  acute  febrile  disease,  known 
in  these  localities  as  spotted  fever,  is  encountered 
in  the  months  of  spring.  The  disease  is  defined  by 
Maxey  as  ^^an  acute,  endemic,  non-contagious,  but 
probably  infectious,  febrile  disease,  characterized 
clinically  by  a  continuous  moderately  high  fever, 
severe  arthritic  and  muscular  pains,  and  a  pro- 
fuse petechial  or  purpural  eruption  in  the  skin, 
appearing  first  on  the  ankles,  wrists  and  forehead, 
but  rapidly  spreading  to  all  parts  of  the  body.'' 

In  1902-03,  Wilson  and  Chowning  studied  many 
cases  of  the  disease  in  Montana,  and  described  as 
the  cause  a  protozoon  organism  which  they  con- 
sider as  a  piroplasma  {PiropJasma  liominis).  The 
organism  is  a  hematozoon,  occurring  within  the 
erythrocytes.  Young  cells  resemble  the  "hyaline 
bodies"  of  malaria,  are  of  ovoid  shape,  1  micron 
thick  and  1  to  2  microns  long,  and  usually  occur  in 
pairs,  but  sometimes  in  numbers  of  4  to  16,  within 
an  erythrocyte.  The  smaller  ends  of  pairs  often 
are  directed  toward  each  other,  and  they  may  be 


SPOTTED     FEVER.  721 

connected  by  a  fine  filament.  They  occur  both  in 
the  red  corpuscles  and  in  the  plasma.  As  they 
grow  larger,  two  to  three  by  three  to  five  microns, 
only  one  parasite  usually  is  found  within  an  ery- 
throcyte, and  in  this  stage  they  show  active  ame- 
boid movement  with  the  formation  of  pseudopodia. 
Eventually  they  assume  a  spherical  form  in  fresh 
preparations.  They  were  able  to  transfer  the  in- 
fection to  rabbits  by  the  inoculation  of  infected 
blood. 

After  identifying  the  organism  as  a  piroplasma 
and  having  in  mind  the  part  that  ticks  play  in  the 
transmission  of  Texas  fever,  and  perhaps  piroplas- 
mosis  in  other  animals  (horse,  sheep,  dog),  Wilson 
and  Chowning  directed  their  attention  to  the  ques- 
tion of  tick  bites  in  those  who  become  infected. 
It  developed  that  of  the  twenty-three  cases  exam- 
ined in  1903  all  had  been  bitten  by  ticks,  and 
fourteen  had  been  bitten  in  from  two  to  eight 
days  before  the  onset  of  the  disease.  They  con- 
cluded that  the  disease  is  transmitted  in  this 
manner. 

They  also  searched  for  some  other  host  than 
man,  in  which  the  parasites  might  flourish  contin- 
uously and  constitute  a  source  of  infection  for  the 
ticks.  This  they  believe  was  found  in  a  certain 
gopher  (Spermopliilus  columhianus) .  On  the  west 
side  of  the  river — that  side  in  which  the  disease 
attacks  man — they  found  the  erythrocytes  of  about 
20  per  cent,  of  the  gophers  infected  with  a  parasite 
similar  to  that  found  in  man.  On  the  other  hand, 
the  blood  of  sixty-two  gophers  from  the  uninfected 
side  of  the  river  showed  no  parasites.  "Early  in 
the  spring  the  spermophile  is  said  to  harbor  great 


Animals. 


722  INFECTION     AND     IMMUNITY. 

numbers  of  ticks/^     Similar  parasites  were  found 
in  no  other  species  of  animals. 

Stiles,  in  later  investigations,  could  not  confirm 
the  results  of  AVilson  and  Chowning,  being  unable 
either  to  find  the  parasites  which  they  described  in 
man,  or  to  accept  the  tick-gopher  hypothesis. 
infectiveness  McCalla  and  Brcrcton  infected  two  individuals 
other  successively  by  the  bite  of  a  tick  which  they  had 
removed  from  one  of  their  patients. 

Eicketts  and  his  collaborators  have  shown  that 
spotted  fever  can  be  reproduced  with  great  con- 
stancy in  the  guinea-pig  by  the  injection  of  in- 
fected blood  or  the  organs  or  eggs  of  infected 
ticks.  The  symptoms  of  spotted  fever  in  the 
guinea-pig  appear  after  an  incubation  period  of 
from  two  to  five  days.  There  is  a  sudden  rise  in 
temperature  to  105°  or  106°  F.,  with  a  general- 
ized roseolar  eruption.  Swelling  and  hemorrhage 
of  the  scrotum  or  vnlva  occurs.  The  symptoms  are 
diagnostic  when  they  occur  typically.  The  mon- 
key, rabbit,  horse  and  at  least  five  species  of  small 
wild  animals  have  a  greater  or  less  degree  of  sus- 
ceptibility. 

Eicketts  and  King,  working  independently,  were 
able  to  transmit  spotted  fever  from  diseased  to 
normal  guinea-pigs  by  allowing  ticks  which  had 
fed  on  diseased  pigs  to  bite  normal  pigs.  Eicketts 
and  Wilder  were  able  to  show  that  up  to  50  per 
cent,  of  infected  ticks  transmitted  the  infection  to 
their  young.  It  was  found  that  nymphs  develop- 
ing from  infected  larvae  were  infectious  for  guinea- 
pigs,  and  that  in  a  similar  way  adult  ticks  devel- 
oping from  nymphs  were  able  to  transmit  spotted 
fever.    Naturally  infected  ticks  were  discoveerd  in 


SPOTTED     FEVER.  723 

1907.  In  order  to  ascertain  the  probable  source 
of   the   virus   as   occurring  in  the   tick,   Eicketts  * 

showed  that  ground  squirrels,  rock  squirrels,  chip- 
munks and  ground-hogs  were  susceptible  to  the 
disease. 

Eicketts  concludes  as  follows  as  to  the  mainte-  Maintenance. 
nance  of  spotted  fever:  ^'In  accordance  with  the 
results  and  deductions  which  have  been  outlined, 
it  is  conceived  that  spotted  fever  is  maintained  as 
follows :  A  certain  percentage  of  the  female  ticks 
which  have  acquired  the  disease  as  a  consequence 
of  feeding  on  animals,  the  latter  having  been  in- 
fected by  other  ticks,  transmit  the  disease  to  their 
offspring  through  the  Qgg.  The  new  generation, 
during  the  process  of  feeding,  transfer  the  virus 
to  certain  of  the  susceptible  small  wild  animals 
(ground  scjuirrels^  rock  squirrels,  chipmunks, 
ground  hogs,  and  perhaps  others),  and  this  may 
take  place  during  either  the  larval,  nymphal  or 
adult  stage,  hence  at  various  times  of  the  year. 
During  the  infection  of  the  wild  animal  it  is  re- 
quired that  hitherto  normal  ticks,  either  as  larvae, 
nymphs  or  adults,  acquire  the  disease  by  feeding 
simultaneously  with-,  or  shortly  after,  the  feeding 
of  the  infected  ticks.  Eegardless  of  the  tick's 
stage  of  development  at  the  time  it  acquired  the 
disease,  the  virus  is  retained  into  the  adult  period, 
and  in  certain  of  the  females  reaches  the  germ 
cells  and  again  appears  in  the  next  generation. 
The  infection  of  man  is  an  unessential  incident 
for  maintenance,  and  depends  on  the  occasional 
and  accidental  bite  of  the  infected  adult  tick." 

The    virus    of    spotted    fever    is    not   filterable 
through   Berkefeld   candles.     The   eggs   of   infec- 


724 


INFECTION     AND     IMMUNITY. 


Microbic  tious  ticks  were  found  b}^  Eicketts  to  contain  a 
Etioiofiry.  jg-pgg  number  of  small  polar  staining  bacilli. 
These  organisms  were  agglutinated  in  high  dilu- 
tion by  the  serum  of  spotted  fever  cases,  but  are 
also  found  in  the  eggs  of  non-virulent  ticks.  At- 
tempts at  cultivation  by  Eicketts  and  Heinemann 
have  been  negative. 
Immunity.  No  authoritative  report  of  a  second  attack  of 
spotted  fever  is  on  record.  According  to  Eicketts 
and  Gomez,  an  attack  of  spotted  fever  in  the 
guinea-pig  and  monkey  produces  a  strong  active 
immunity  of  long  duration.  This  immunity  is 
characterized  by  the  presence  of  protective  anti- 
bodies in  the  serum  which  may  be  demonstrated 
by  injecting  mixtures  of  virus  and  immune  serum. 
The  concentration  of  the  antibodies  in  the  blood 
of  the  immune  animal  undergoes  a  decrease  in  the 
course  of  several  weeks. 

The  female  that  has  recovered  from  spotted 
fever  transmits  immunity  to  her  young.  The 
young  are  immune  even  when  the  female  acquired 
her  immunity  several  months  before  impregna- 
tion. The  immunity  of  the  young  does  not  de- 
pend on  the  ingestion  of  milk  from  the  immune 
mother.  The  character  of  the  inherited  immunity 
has  not  yet  been  determined,  although  it  is  pre- 
sumptively a  passive  immunity  that  differs  from 
the  passive  immunity  conferred  by  the  injection 
of  immune  serum  by  its  longer  duration.  The 
long  duration  of  the  inherited  immunity  may 
depend  on  the  longer  time  required  for  the  elimi- 
nation of  large  quantities  of  protective  substances. 

Passive  immunity  may  be  established  in  the 
healthy  guinea-pig  by  the  injection  of  blood   or 


TYPHUS     FEVER. 


725 


serum  from  the  immune  guinea-pig.  The  immune 
defibrinated  blood  contains  antibodies  in  such  con- 
centration that  0.1  c.  c.  often  protects  against  1 
c.  c.  of  third-day  virus,  representing  anywhere 
from  30  to  100  minimum  pathogenic  doses.  In 
other  instances  0.3  or  0.4  c.  c.  of  immune  blood 
are  required  for  this  degree  of  protection.  When 
1  c.  c.  of  strong  immune  blood  is  injected  subcu- 
taneously  into  healthy  guinea-pigs,  the  passive 
immunity  is  still  present  in  marked  degree  after 
twenty  days;  after  thirty-eight  days  it  is  present 
only  in  such  degree  that  a  mild  course  of  spotted 
fever  results  when  virus  is  injected;  after  forty- 
five  days  it  is  no  longer  manifest.  It  is  possible 
that  passive  immunity  would  not  last  so  long  if 
the  immune  blood  is  injected  into  a  foreign 
species. 

The  guinea-pig  xxijy  be  protected  against  spotted 
fever  f ollowino-  its  inoculation  with  infected  blood, 
provided  the  immune  blood  is  administered  on 
the  second  or  third  day  after  inoculation. 

The  work  of  Eicketts  indicates  that  efforts  at 
prophylaxis  are  to  be  directed  toward  the  exter- 
mination of  ticks  and  the  wild  animals  which 
harbor  them. 

Serotherapy  will  probably  depend  on  the  culti- 
vation of  the  microbic  cause  of  the  disease. 


Propliylaxis 
aad.  Sero- 
tlierapT. 


IV.   TYPHUS  FEVER.    - 

Typhus  is  now  a  rare  disease.    It  is  endemic  on   occarrence 
a  small  scale  in  London,  Glasgow  and  Liverpool,  Jfoi-^n^s*" 
and  cases  occur  in  the  larger  cities  of  Ireland.    In 
epidemic  form  it  attacks  localities  in  which  the 
hygienic  conditions  are  bad.    The  contagion  seems 


726  INFECTION     AND     IMMUNITY. 

to  fasten  itself  in  such  localities  and  does  not  ex- 
tend with  rapidity  to  neighboring  communities  in 
which  good  hygiene  and  cleanliness  prevail;  it  is 
particularly  a  disease  of  the  poor,  the  filthy  and 
the  underfed.  Healthy,  clean  and  well-nour- 
ished persons  who  enter  an  infected  district  and 
come  in  contact  with  the  patients  are  subject  to 
attack.  Typhus  has  always  been  considered  a  very 
contagious  disease.  It  has  been  noted  repeatedly, 
however,  that  when  patients  are  removed  to  a  hos- 
pital and  kept  under  clean  and  hygienic  conditions 
with  plenty  of  fresh  air  that  infection  of  attend- 
ants and  ph3^sicians  is  relatively  infrequent. 

Mexican  typhus,  or  tabardilli,  resembles  Euro- 
pean t3^phus  closely,  but  has  a  longer  incubation 
period  and  reaches  the  crisis  a  few  days  before 
the  European  typhus  does.  There  is  less  tendency 
to  confluent  eruption  and  hemorrhage. 
Pathose-  Nicolle  and  his  associates  were  able  to  produce 
"Animals^  typhus  in  the  chimpanzee  by  the  injection  of 
blood  from  European  typhus  patients  and  in  a 
similar  way  in  the  Macacus  monkey  with  blood 
from  infected  chimpanzees.  Direct  transmission 
from  man  to  the  macacus  was  not  accomplished. 
Anderson  and  Goldberger  were  able  to  transmit 
tabardillo  directly  to  the  monkey  by  inoculations 
with  the  blood  of  typhus  patients.  Their  results 
were  confirmed  by  Eicketts  and  Wilder,  who  deter- 
mined the  following  points:  "1.  Macacus  rhesis 
can  be  infected  with  tabardillo  invariably  by  the 
injection  of  virulent  blood  from  man  taken  on 
the  eighth  to  tenth  day  of  fever.  2.  Attempts  to 
maintain  typhus  in  the  monkey  by  passage  through 
other   monkeys   were   unsuccessful.     3.   Monkeys 


TYPHUS    FEVER.  727 

may  pass  through  an  attack  of  typhus  so  mild 
that  it  can  not  be  recognized  clinically.  Vaccina- 
tion results/' 

Nicolle  succeeded  in  transmitting  the  typhus  Transmission. 
fever  of  Tunis  from  chimpanzees  to  monkeys  by 
means  of  the  common  body  louse.  Anderson  and 
Goldberger  and  Ricketts  and  Wilder  succeeded  in 
producing  tabardillo  in  the  monkey  through  the 
bite  of  the  louse.  The  lice  were  allowed  to  feed 
on  the  blood  of  patients  with  tabardillo  and  sub- 
sequently permitted  to  bite  the  monkeys.  Eicketts 
and  Wilder  also  demonstrated  that  infected  lice 
transmitted  the  infection  to  their  eggs^  which  gave 
rise  to  lice  capable  of  infecting  monkeys.  Their 
observations  of  the  spread  of  the  disease  render  it 
reasonably  certain  that  lice  are  the  ordinary  means 
of  transmission.  Studies  on  the  bed  bug  and  flea 
indicate  that  they  play  no  part  in  the  spread  of 
this  infection. 

The    virus    of   typhus    fever    is    not    filterable.   Microbic 

,  1      T      •         IT         Etiology. 

Various  organisms  have  been  described  m  the 
blood.  Eicketts  and  Wilder  describe  a  small  bac- 
illus in  stained  blood  preparations.  The  organism 
resembles  the  plague  bacillus  and  those  organisms 
described  in  spotted  fever.  The  organism  was 
also  found  in  the  intestinal  tract  of  infected  lice. 
Cultivation  was  unsuccessful.  Further  studies 
are  necessary  to  establish  the  etiologic  relation- 
ship to  typhus. 

The  production   of  immunity  through   a  light  immnnitF. 
attack  of  typhus  in  the  monkey  has  already  been 
mentioned.    The  serum  of  convalescents  is  said  to 
be  curative  in  a  moderate  degree  (Legrain), 


TransBilssioii. 


728  INFECTION'     AND     IMMUNITY. 

V.    DENGUE   FEVEPi. 

Dengue  occurs  in  numerous  countries  which  af- 
ford a  warm  climate.  It  is  endemic  in  Egypt, 
Arabia,  Senegambia,  Honduras,  the  Bermudas, 
and  the  Sandwich  Islands.  Important  centers  for 
the  origin  of  epidemics  are  the  lesser  Antilles  of 
the  Western  Hemisphere,  the  Red  Sea  Coast, 
and  Senegambia  (de  Brun,  cited  by  Scheube).  It 
occurs  in  our  southern  states  and  in  Mexico.  It 
may  be  introduced  into  new  regions  by  means  of 
infected  ships. 

"Dengue  fever  is'  an  acute  infectious  disease, 
distinguished  by  the  appearance  of  an  initial  and 
terminal  polymorphous  eruption  and  accompanied 
by  severe  articular  and  muscular  pains.'^  Corre- 
sponding with  the  two  eruptions,  there  are  charac- 
teristically two  periods  of  temperature  separated 
by  a  short  period  of  apyrexia.  The  intense  muscu- 
lar pains  and  asthenia  resemble  those  of  influenza, 
the  respiratory  affections  of  the  latter  being  absent, 
however.  The  incubation  period  varies  from  a  few 
hours  to  four  or  five  days,  usually  one  or  two,  and 
the  entire  duration  from  six  to  seven  days. 

Eberle,  in  1904,  advanced  the  hypothesis  that 
dengue  is  transmitted  by  a  mosquito  (Culcx  fati- 
gans).  He  described  a  "plasmeba'^  in  the  blood 
of  patients  with  the  disease.  Other  observers  have 
failed  to  find  protozoa  in  the  blood.  Ashburn  and 
Craig  (1907)  were  able  to  transmit  the  disease  to 
healthy  men  by  injecting  the  blood  of  infected 
individuals.  They  were  able  to  produce  the  dis- 
ease by  allowing  mosquitoes,  which  had  fed  on 
dengue  patients,  to  bite  healthy  men.  Their 
studies  also  showed  that  the  distribution  of  the 
Culex  fatagans  corresponded  with  that  of  dengue, 


ACUTE    ARTICULAR    RHEUMATISM.         720 

thus  putting  tlie  liypothesis  of  Eberle  on  a  firm 
basis. 

Ashburn  and  Craig  were  unable  to  find  the  or-  Fiiterabiiity 
ganism  responsible  for  the  disease,  but  demon- 
strated that  the  filtered  blood  of  infected  persons 
can  produce  the  disease  in  healthy  subjects.  They 
were  unable  to  cultivate  or  detect  in  other  ways 
any  micro-organisms. 

According  to  Ashburn  and  Craig,  an  attack  of 
dengue  confers  immunity.  They  were  unable  to 
produce  a  second  attack  by  the  injection  of  infec- 
tious blood  in  individuals  who  had  recovered  from 
the  disease. 

VI.    ACUTE   ARTICULAR   RHEUMATISM. 

(See  p.  525.) 

VII.     SMALLPOX    AND    VACCINIA. 

Vaccinia  and  smallpox  may  be  considered  to-  Relation  of 
gether,  having  in  mind  the  likelihood  or,  indeed,  smaiipox. 
the  certainty,  that  they  have  a  common  etiology. 
This  view  seems  the  only  possible  one,  in  spite  of 
our  uncertainty  as  to  the  exact  nature  of  the  cause. 
To  hold  a  different  view  would  be  to  acknowledge 
that  immunization  with  one  kind  of  microbe  may 
confer  immunity  of  the  strongest  and  most  spe- 
cific character  against  another,  a  condition  for 
which  we  could  find  no  parallel. 

More    satisfactory    knowledere,    however,    comes   inoculation  of 

.  <.  ?i  .     .  *^^    Cal'    with 

from  actual  conversion  oi  smallpox  virus  into  vac-  smaiipox. 
cine  virus  by  passing  the  former  through  cows. 
Abbot  quotes  W.  J.  Simpson  as  follows :  "In  No- 
vember, 1885,  with  smallpox  lymph  from  an  nn- 
vaccinated  patient,  1  inoculated  a  cow  with  fifth- 
day  lymph  and  a  ewe  with  eight-day  lymph  from 


730  INFECTION    AND     IMMUNITY. 

the  same  patient.  Both  presented  vesicles  on  the 
seventh  da}^,  the  lymph  of  which  I  sent  to  London 
to  be  used  by  Dr.  Cory,  the  director  of  the  Animal 
Vaccine  Institute  of  London.  This  calf  lymph, 
which  Dr.  Cory  passed  through  a  second  calf  before 
using  it  on  children,  was  the  starting  point  of  a 
new  vaccine  at  the  institute.  Between  Nov.  21, 
1885,  and  May  6,  1886,  1,247  children  had  been 
vaccinated  with  this  lymph  and  gave  98.4  per 
cent,  insertions  of  success." 

Concerning  the  changes  which  smallpox  virus 
undergoes  in  the  cow,  as  a  result  of  which  it  loses 
permanently  the"  power  of  causing  smallpox  in 
man,  we  have  no  knowledge,  aside  from  the  hy- 
pothesis of  Councilman  and  others  mentioned  below. 

Etiology.  We  may  pass  over  the  various  bacilli  and  cocci 
which  have  been  described  as  causing  vaccinia  and 
smallpox  with  the  remark  that  none  of  them  are 
of  primary  significance,  but  that  they  have  been 
either  accidental  contaminations  or  the  causes  of 
secondary  infections  during  the  course  of  the  dis- 
ease. 

Theories.  There  are  two  chief  theories  as  to  the  cause  of 
smallpox  (and  vaccinia)  to-day.  One,  that  the  virus 
is  an  ultra-microscopic  and  uncultivatable  organ- 
ism ;  and  a  second,  that  it  is  represented  by  certain 
protozoon-like  bodies  seen  in  the  specific  lesions 
(vesicles,  pustules)  of  both  vaccinia  and  smallpox. 
Concerning  the  first  theory  we  know  nothing  be- 
yond the  observation  of  Parke  that  the  virus  of  both 
vaccinia  and  variola  did  not  pass  through  Berke- 
feld  and  Chamberland  filters  under  the  conditions 
of  hi?  experiments.  Of  the  second  theory  a  brief 
review  may  be  given. 


CYTORYCTES    VARIOLA. 


731 


Protozoon-like  bodies  have  been  seen  by  many  cytoryctes 
observers  and  were  first  brought  into  causal  rela-  Protozoon.  c?) 
tion  with  smallpox  by  Van  der  Loeff  and  by  L. 
Pfieffer  (1887).  Guarnieri  (1892),  however,  gave 
the  subject  its  present  impetus  by  a  careful  study 
of  these  forms  as  seen  in  vaccinia  and  gave  to  the 
hypothetical  organism  the  name  of  Cytoryctes  vac- 
cinice,  s.  variolce.  The  bodies  were  found  within 
the  deep  epithelial  cells  in  the  pustules  of  vaccinia 
and  smallpox  and  in  the  lesions  produced  on  the 
cornea  of  the  rabbit  by  inoculation  with  the  viruses 
of  vaccinia  and  smallpox.  They  lie  within  clear 
spaces  in  the  protoplasm  of  the  cells,  vary  in  size 
from  that  of  a  micrococcus  to  that  of  an  epithelial 
nucleus  and  multiply,  it  was  supposed,  by  binary 
division.  When  mounted  in  hanging-drops  of  the 
vesicular  fluid  they  showed  ameboid  movements. 
Confirmatory  work  came  from  others,  and  partic- 
ularly Wasielewski,  who  concluded  that  the  "vac- 
cine bodies"  are  perfectly  characteristic,  that  they 
are  never  found  in  normal  or  other  pathological 
conditions  of  the  skin,  that  they  can  not  originate 
from  leucocytes  or  epithelial  cells,  and  hence  can 
not  be  accidental  "cell  inclusions."  Filtered  virus 
produced  no  lesions  in  the  cornea  of  the  rabbit. 

Eecently  Councilman,  Magrath  and  Brincker- 
hoff  have  studied  this  supposed  organism  in  great 
detail  and  find,  in  addition  to  the  forms  in  the  cy- 
toplasm (cytoplasmic  parasites),  still  others  within 
the  nucleus  of  the  epithelial  cells  of  the  vesicles 
and  pustules.  They  express  the  belief  that  the  or- 
ganism first  gains  entrance  to  the  cytoplasm  of  the 
cells,  and  after  a  period  of  "multiplicative  prolif- 
eration," the  products  of  the  latter  process  pene- 
trate the  nuclei  of  the  epithelial  cells  and  there 


Work  of 
Councilman 
and   Otliers. 


732  IXFECTION     AXD     IMMUNITY. 

undergo  another  type  of  proliferation.  Calkins, 
the  zoologist,  after  studying  the  material,  shares 
their  views  and  has  constructed  a  life  cycle  of  the 
parasite  from  the  various  forms  which  he  found  in 
fixed  and  stained  preparations. 

Life  History       The    smallest    recognizable    forms    in    the    cytoplasm 
of  Cytoryotes.    measure  about  0.7  of  a  micron  and  lie  in  a  vacuole  in 

the  cytoplasm  near  the  nucleus.  Calkins  interprets 
these  as  "gemmules"  and  as  products  of  the  prolifera- 
tion of  the  parasite  at  the  primary  point  of  infection 
( lungs  (  ? )  ) .  Somewhat  larger  forms  ( 3  microns )  con- 
taining a  vacuole  with  a  central  point  staining  with 
methylene  blue,  represent  "gemmules"  which  have  grown 
and  have  become  somewhat  differentiated.  The  periphery 
of  the  organism  becomes  differentiated  also  by  the  for- 
mation of  minute  dots  which  may  eventually  be  stained 
by  a  special  method.  During  this  stage  the  organism 
Cytoplasmic  "often  is  spherical,  but  may  be  fusiform,  pyriform  or 
stages,  ameboid,  while  pseudopodia  are  frequently  caught  in 
various  degrees  of  extension."  No  definite  nucleus  is 
discernible,  but  material  corresponding  to  nuclear  sub- 
stance is  distributed  somewhat  generally  through  the 
parasitic  cell.  Certain  granules  are  distributed  through- 
out the  body  of  the  organism,  and  these  granules  eventu- 
ally give  rise  to  the  "gemmules"  or  young  parasites 
which  become  free  by  the  disintegration  of  the  mother 
cell. 

Howard  and  Perkins  find,  in  addition  to  the  cyto- 
plasmic stage  of  Councilman  and  his  co-workers,  a  sec- 
ond cytoplasmic  stage,  the  products  of  which  penetrate 
the  nucleus  to  institute  the  intranuclear  stages.  Cal- 
kins speaks  of  the  fate  of  the  gemmules  as  follows: 
"The  germs  formed  by  the  multiplicative  reproduction 
of  the  cytoplasmic  ameboid  form  of  the  parasite  may 
develop  into  new  cytoplasmic  organisms  or  ultimately 
may  become  germ  cells  within  the  nucleus  of  the  epithe- 
lial cell.  In  the  latter  case  they  develop  into  struc- 
tures which  I  regard  as  gametocytes.  The  resulting 
zygote  (formed  by  conjugation  of  the  gametes)  is  the 
ameboid  pansporoblast  mother  organism." 


CYT0RYCTE8    VARIOLA. 


■33 


The  conclusion  that  conjugation  takes  place  is  based 
on  certain  analogies  with  other  micro-organisms,  rather 
than  on  observation  of  the  phenomenon.  This  intra- 
nuclear mother  organism,  the  product  of  conjugation, 
finally  grows  to  a  size  of  10  to  12  microns  and  forms 
within  it  from  eight  to  twenty  "primary  sporoblasts." 
The  young  sporoblasts  are  eventually  liberated  from  the 
mother  cell  and  are  at  first  solid  and  homogeneous,  like 
the  gemmules,  but  later  when  they  have  reached  a  size  of 
ll^  to  2  microns  small  vacuoles  appear  in  the  peripheral 
ring  of  substance  and  in  each  vacuole  a  young  spore  is 
formed.  The  formation  of  these  spores  terminates  the 
"primary  nuclear  phase"  of  the  organism.  These  spores, 
still  within  the  nucleus  of  the  epithelial  cell,  become, 
in  their  turn,  sporoblasts,  and  the  formation  of  a  large 
number  of  secondary  spores  within  them  constitutes  the 
secondary  nuclear  phase  of  a  parasite.  In  the  mean- 
time the  nucleus  of  the  epithelial  cell  has  degenerated, 
and  the  secondary  sporoblast  with  its  contained  spores 
escapes  first  into  the  cytoplasm  and  eventually  into  the 
pericellular  space.  In  accordance  with  this  conception 
the  intranuclear  process  is  well  calculated  to  give  rise 
to  a  massive  number  of  young  parasites  within  the  body. 
Councilman,  Magrath  and  Brinckerhoff  state  that  after 
the  tenth  day  of  the  disease  the  parasites  become  more 
and  more  difficult  of  recognition  by  microscopic  methods. 
However,  Brinckerhoff  found  that  even  the  desiccated 
crusts  of  pustules  and  vesicles  produce  typical  lesions 
on  the  cornea  of  the  rabbit.  These  forms  have  never 
been  recognized  positively  in  the  blood  of  patients,  and 
Magrath  and  Brinckerhoff  were  not  able  to  produce  le- 
sions in  the  rabbit's  cornea  by  inoculation  of  variolous 
blood.  The  general  distribution  of  the  lesions  in  the 
skin  and  the  occurrence  of  fetal  smallpox  gives  us  abun- 
dant reason  for  believing  that  the  blood  stream  is  in- 
vaded by  the   parasites. 

It  was  stated  above  that  bodies  of  the  general  nature 
of  those  described  are  found  in  vaccinia  as  well  as  in 
smallpox,  and  this  occurrence  is  some  added  reason  for 
believing  that  Cytoryctes  variolne,  s.  vacciniw,  is  the 
cause  of  these  processes.  It  is  a  most  interesting  and 
important   observation   by    the   American   authors   cited 


\uclear 
.Stages. 


Cytorycetes 
in   Vaccinia. 


734  INFECTION     AND     IMMUNITY. 

that  the  intranuclear  stage  of  the  parasite  does  not 
occur  in  vaccinia  (Tyzzer),  and  we  are  led  to  believe 
that  this  is  an  important  differential  point  between 
vaccinia  and  smallpox.  Assuming  that  the  bodies  in 
question  cause  the  disease,  the  thought  is  pertinent  that 
the  difference  in  virulence  between  vaccinia  and  variola 
inoeulata  may  depend  on  the  failure  of  the  intranuclear 
cycle  to  appear  in  vaccinia. 

The  work  of  Guarnieri,  and  particularly  that  of 
Councilman,  Magrath  and  Brinckerhoff,  is  most 
suggestive,  and  ardent  supporters  of  their  views 
have  appeared  with  corroborative  work  (e.  g.,  How- 
ard).    At  the  same  time  many  skilled  observers 
discredit  entirely  the  parasitic  nature  of  the  bodies 
described,   interpreting  them   rather   as   products 
of  degeneration  of  the  epithelial  cells  and  nuclei 
or  as  inclusions  of  other  tissue  cells  (e.  g.,  leuco- 
cytes, Borrel)  or  fragments  of  other  nuclei.  Ewing 
expresses  similar  views.    The  state  of  the  question 
is  such  that  further  study  is  urgently  called  for. 
Infection       ^^G  havc  uo  positivc  knowledge  as  to  infection 
Atrinm.   ^trium  iu  smallpox,  although  the  existence  of  a 
"contagious  zone"  of  atmosphere  about  the  patients 
is  good  ground  for  the  belief  that  invasion  takes 
place  through  the  respiratory  passages.  The  disease 
which  follows  introduction  of  the  virus  into  the 
skin  is  spoken  of  as  variola  inoeulata,  and  is  much 
less  severe  than  smallpox.    We  are  also  ignorant  to 
a  large  degree  of  the  means  of  excretion  or  dissem- 
mination  of  the  virus.     Osier  states  that  the  virus 
Dissemina-  "cxists  in  the  secrctious  and  excretions  and  in  the 
****"*  exhalations  from  the  lungs  and  skin.''    The  dried 
epithelial  cells  which  are  continuously  thrown  off 
are  no  doubt  a  most  important  means  of  dissemina- 
tion.    Infection  may  be  transmitted  by  means  of 
clothing  or  other  materials  which  have  been  in  con- 


GYT0RYCTE8    VARIOLA. 


736 


tact  with  patients,  and  the  disease  may  be  carried 
to  others  from  the  sickroom  by  a  healthy  person. 
Epidemiologic  experience  teaches  that  the  virus  is 
one  of  great  resistance  and  tenacity. 

The  incubation  period  in  variola  falls  within  the  cyciic 
extremes  of  eight  to  twenty  days,  most  commonly  symptoms. 
from  nine  to  fifteen  days.  The  stage  of  invasion, 
or  the  primary  fever,  terminates  the  incubation 
period,  and  during  this  time  the  initial  rash  ap- 
pears, accompanied  by  moderate  hyperleucocytosis. 
On  the  third  to  the  fourth  days  the  remission  sets 
in,  the  number  of  leucocytes  in  the  blood  decreases 
to  normal  or  below  normal,  and  cutaneous  lesions 
make  their  appearance,  and  in  the  course  of  forty- 
eight  hours  show  a  vesicular  nature.  When  the 
umbilicated  vesicles  are  changed  into  pustules  the 
temperature  again  rises  (secondary  fever)  and  hy- 
perleucocytosis again  develops.  This  much  only 
of  the  clinical  picture  is  mentioned  to  emphasize 
the  cyclic  nature  of  the  phenomena ;  one  may  well 
suspect  that  the  organism  causing  such  a  disease 
undergoes  particular  phases  of  development  which 
in  some  way  are  related  to  the  well-known  clinical 
cj^cle. 

Epidemics  are  sometimes  of  so  mild  a  charac- 
ter that  the  patients  are  not  bed-ridden  and  may 
be  found  in  the  pursuit  of  their  occupations  in 
spite  of  well-marked  eruptions.  Such  occurrences 
can  be  referred  only  to  a  virus  of  low  pathogeni- 
city. Even  mild  epidemics,  however,  may  be  ac- 
companied by  severe  and  fatal  cases.  Cases  of  am- 
bulatory smallpox  are  most  important  factors  in 
spreading  the  disease. 

We  have  nothing  more  than  presumptive  knowl- 
edge concerning  the  distribution  of  the  virus  in 


Variations 
in  Virulence. 


736 


INFECTION     AND     IMMUNITY. 


Secondary 
Infections. 


Distribution  the  body  aside  from  its  occurrence  in  the  skin  and 
*Body!  mucous  membranes.  We  may  feel  certain,  how- 
ever, that  the  infection  is  systemic.  The  lesions 
of  the  skin  are  of  such  a  nature  that  they  are 
generally  regarded  as  of  embolic  character,  which 
presupposes  blood  infection;  and  transmission  of 
the  disease  through  the  placenta  is  decisive  proof 
of  a  general  distribution  of  the  virus  at  some  stage 
of  the  process.  The  failure  to  cause  vaccinia  in 
the  cornea  of  the  rabbit  by  inoculating  the  blood 
of  patients  (cited  above)  may  indicate  that  the 
virus  is  present  in  the  blood  in  small  quantity  or 
that  circulating  organisms  are  eventually  de- 
stroyed. The  intoxication  of  smallpox  is  mani- 
festly general. 

In  few  diseases  does  secondary  infection  play  so 
important  a  role  as  in  smallpox.  When  the  cu- 
taneous lesions  have  become  pustular  they  usually 
contain  pyogenic  cocci,  although  they  may  be  ab- 
sent. It  is  somewhat  strange  that  streptococci  are 
more  often  encountered  than  staphylococci,  in 
view  of  the  normal  presence  of  the  latter  in  the 
epidermis.  Fatal  cases  are  almost  without  excep- 
tion accompanied  by  general  streptococcus  infec- 
tions, and  Councilman  believes  these  organisms 
are  more  important  as  a  cause  of  death  than  the 
specific  virus. 
Prophylaxis.  Succcssful  prophylaxJs  involves  universal  vac- 
cination, in  addition  to  special  measures  which  are 
demanded  in  the  presence  of  the  disease:  isola- 
tion of  the  sick  until  desquamation  is  complete, 
antiseptic  baths,  and  disinfection  and  fumigation 
as  currently  practiced. 

Interesting  matters  of  history  are  the  facts  that 
protective  inoculation  against  smallpox  was  prac- 


VACCINATION.  737 

ticed  in  fairly  ancient  times  by  rather  primitive   Discovery  ©f 

•^  J  r  vaccination. 

races,  and  that  Lady  Mary  Wortley  Montague 
introduced  this  method  into  Europe  in  1718. 
This  was  not  the  vaccination  in  vogue  to-day, 
however,  but  rather  the  inoculation  of  virulent 
virus  from  the  pustules  of  the  diseased  into  the 
healthy.  As  mentioned  in  one  of  the  earlier  chap- 
ters, this  procedure  commonly  produced  a  mild 
type  of  disease  (variola  inoculata)  which  ren- 
dered the  individual  immune  to  virulent  small- 
pox. 

Everyone  knows  that  the  vaccination  of  to-day,  .lenner. 
i.  e.,  the  substitution  of  the  virus  of  cowpox  for 
that  of  smallpox,  was  the  discovery  of  Jenner 
(1798),  and  we  need  offer  no  comments  concern- 
ing its  efficacy  nor  repeat  the  well-earned  epithets 
which  have  been  applied  to  the  rare  species  of  dis- 
believers. Nothing  is  more  certain  than  that 
smallpox  has  ceased  to  be  a  world  pest  only  be- 
cause of  the  continued  Jennerization  of  the  race. 

The  essential  points  established  by  Jenner  are 
the  following:  1.  That  the  vaccine  disease 
casually  communicated  to  man  has  the  power  of 
rendering  him  insusceptible  to  smallpox.  2.  That 
the  specific  cowpox  alone,  and  not  other  eruptions 
affecting  the  cow  which  might  be  confounded  with 
it,  has  this  protective  power.  3.  That  the  cow- 
pox  may  be  communicated  at  will  from  the  cow  to 
man,  by  the  hand  of  the  surgeon,  whenever  the 
requisite  opportunity  exists.  4.  That  the  cowpox, 
once  engrafted  on  the  human  subject,  may  be  con- 
tinued from  individual  to  individual  by  successive 
transmissions,  conferring  on  each  the  same  im- 
munity against  smallpox  as  was  produced  in  the 


738  INFECTION     AND     IMMUNITY. 

one   first   infected   directly   from   the   cow    (cited 
from  S.  W.  Abbott). 

Httmait^Kert  YoT  at  Icast  half  a  century  following  Jenner's 
discovery  humanized  lymph  was  used  for  vacci- 
nation, new  patients  being  inoculated  by  means 
of  points  prepared  from  vesicles  of  previous  cases, 
or  with  the  fresh  lymph  from  such  cases.  The  not 
infrequent  transmission  of  syphilis  by  this  means 
was  the  source  of  many  calamities.  Following  the 
precedent  of  Warlemont  in  1868,  the  lymph  of 
cowpox  is  now  the  universal  source  of  vaccina. 
cowpox.  Cowpox  probably  occurs  to  a  greater  or  less 
degree  in  all  countries,  especially  in  the  spring  and 
summer,  attacks  the  udder  and  teats  almost  ex- 
clusively, and  is  accompanied  by  very  mild  con- 
stitutional symptoms.  The  incubation  period  is 
from  three  to  eisjht  davs.  There  is  first  local 
heat,  swelling  and  tenderness,  followed  by  the  for- 
mation of  papules,  which  in  three  or  four  days 
after  their  appearance  are  transformed  into  vesi- 
cles. The  disease  reaches  its  maximum  develop- 
ment at  the  tenth  or  eleventh  day,  the  umbilicated 
vesicles  going  through  the  usual  course  to  crust 
formation. 

^of*  vkc^Vn  "  Calves  and  heifers  from  the  age  of  two  months 
to  two  years  are  best  suited  for  vaccination  in  the 
production  of  lymph  for  commercial  purposes. 
The  region  of  the  flank  or  the  whole  ventral  sur- 
face of  the  body  may  be  inoculated,  and  in  the  lat- 
ter instance  as  many  as  a  hundred  or  more  inser- 
tions may  be  made.  The  skin  is  first  shaved, 
cleansed  with  antiseptics,  and  the  lymph  from  an- 
other calf  is  introduced  by  means  of  a  syringe  or 
by  scarification.  In  some  institutions  long,  very 
superficial  parallel    incisions    are    made  and  the 


VACCINATION.  739 

virus  rubbed  in  witli  a  spatula.  Within  from  five 
(lays  to  a  week  the  vesicles  are  in  sucli  condition 
that  the  lymph  may  be  collected,  the  contents 
either  being  squeezed  out  with  suitably  formed 
forceps  or  scooped  out  with  a  sharp  spoon.  De- 
pending on  the  area  vaccinated,  the  lymph  col- 
lected from  a  single  calf  may  be  sufficient  f(jr 
from  2,000  to  15,000  vaccinations  in  man.  Be- 
cause of  the  immunity  which  is  conferred,  calves 
can  be  used  but  once  for  the  production  of  vaccine 
virus. 

All  other  methods  of  preserving  lymph  have  Giycerinixa- 
been  largely  abandoned  for  the  process  of 
glycerinization,  the  glycerin  being  very  inti- 
mately mixed  with  the  virus  by  mechanical 
means  and  allowed  to  remain  in  this  state  in 
a  cool  place  for  from  six  to  eight  weeks  before 
the  product  is  put  on  the  market.  Dried  vaccine 
on  ivory  points  is  still  used  to  some  extent,  the 
points  being  coated  directly  from  the  vesicles. 
Dried  vaccine  retains  its  power  for  from  two  to 
four  months  or  longer  when  kept  in  a  cool,  dark, 
dry  place.  Glycerin ated  lymph  has  many  advan- 
tages, the  most  important  of  which  relates  to  the  Effect  on 
bactericidal  action  of  the  glycerin  by  which  the  insr  Bacteria. 
lymph  is  freed  from  the  pathogenic  bacteria  (e.  g., 
staphylococci)  which  in  former  times  caused  ser- 
ious complications  in  vaccination.  The  glycerin 
is  supposed  to  destroy  such  organisms  to  a  large 
degree  without,  however,  injuring  the  vaccine 
virus  itself.  It  is  also  stated  that  glycerinated 
lymph  is  much  more  durable  than  the  dried  ;  that 
its  potency  may  be  retained  for  eight  months  or 
longer  under  suitable  conditions.  Eoscnau  has 
recently  called  attention  to  the  fact  that  the  bac- 


740  jxFEcrioy    A\D   7.1/1/ fw/rr. 

tericidal  power  of  olyeerin  has  heen  overestimated, 
and  that  while  it  kills  p3'ogenic  cocci  within  two 
weeks  when  at  the  body  temperature,  such  organ- 
isms may  live  for  months  in  glycerin  when  in  the 
ice  chest;  and,  of  course,  our  glycerinated  virus 
is  kept  in  the  ice  chest.  Tetanus  spores  live  for 
months  in  glycerin  and  glycerin  has  practically 
no  neutralizing  action  on  tetanus  toxin.  Glycerin 
does  have  the  power,  however,  of  attenuating  the 
tetanus  spores,  and  its  slow  bactericidal  action  is 
well  established.  As  stated  above,  the  vaccine 
should  be  glycerinized  for  some  weeks  before  it  is 
put  on  tlie  market.  Gh'cerin  has  the  added  ad- 
vantage for  the  manufacturer  of  enabling  him  to 
dilute  his  lymph  moderately  (from  50  to  60  per 
cent.)  without  impairing  the  virus. 

Of  much  more  importance  for  the  safety  of 
virus  than  glycerinization  are  proper  hygiene  and 
cleanliness  during  the  whole  process  of  prepara- 
tion. The  powers  recently  conferred  on  the  Sur- 
geon-General by  an  act  of  Congress  have  resulted 
in  a  great  improvement  in  the  purity  of  the  vac- 
cine now  on  the  market.^ 

While  it  can  not  be  expected  that  vaccine  will 
be  entirely  free  from  bacteria,  it  is  possible  to  re- 
duce their  number  to  a  low  minimum  and  to  elim- 
inate pathogenic  forms,  particularly  pathogenic 
cocci,  tetanus  and  tubercle  bacilli. 
Vaccination.  The  tcclinic  of  vacciuatiou  is  so  well  known 
that  no  description  is  needed.  It  need  only  be 
stated  that  in  scarifying  it  is  undesirable  to 
cause  hemorrhage  and  that  the  operation  is  a  sur- 
gical  procedure,    demanding   surgical   cleanliness 

1.  John  F.  Andorson  "Federal  Control  of  Vaccine  Virus," 
Jour,  of  the  Amer.  Med.  Assn.,  June  10.  1905. 


VACCINATION.  741 

and  surgical  care  of  the  wound.  As  a  rule  vac-  '^ 
cination  in  man  protects  against  smallpox  for  a 
period  of  six  to  ten  years,  after  which  revaccina- 
tion  is  necessary  for  continued  protection.  It 
shc^uld  not  be  concluded  from  the  negative  out- 
come of  a  single  vaccination  that  the  individual  is 
immune  to  vaccination  and  hence  immune  to 
smallpox,  but  rather,  repeated  attempts  should  be 
made  with  virus  known  to  be  fresh.  It  is  quite 
possible  that  certain  individuals  are  immune  to 
vaccinia,  as  often  stated,  but  they  are  very  rare, 
and  the  condition  should  not  be  recognized  hastily. 
Among  38,000  vaccinations  Dr.  Cory  encountered 
but  one  in  which  a  "take"  could  not  be  obtained 
on  second  trial  (Abbott). 

The  ideal  condition  is  that  all  children  should   when  to 

.  .  Vaccinate. 

be  vaccinated  at  an  early  age  by  requirement  of 
law  as  in  certain  European  countries,  where  it  is 
demanded  within  the  first  few  months  or  the  first 
year  or  two  of  life.  Some  countries  require  re- 
vaccination  before  the  children  are  admitted  to 
school  and  recommend  repetitions  at  suitable  in- 
tervals. 

We  have  no  national  law  on  the  subject  and  the 
state  laws  differ.  In  many  states  children  must 
be  vaccinated  before  they  are  admitted  to  the  pub- 
lic schools,  the  responsibility  sometimes  falling 
on  the  school  and  sometimes  on  the  city  or  town 
authorities.  A  number  of  states  have  no  laws  on 
the  subject,  although  vaccination  is  for  the  most 
part  assured  through  the  requirements  of  the 
state  boards  of  health  and  the  local  authorities. 

When  there  is  danger  of  an  epidemic,  and  in 
known  cases  of  exposure,  vaccination  should  be 
practiced  thoroughly.     Inasmuch   as  the   incuba- 


742 


IXFJX'TJOy     AXD     J]f]fr\ITY 


tion  period  of  vaccinia  is  about  three  days  less 
than  that  of  smallpox,  successful  vaccination  pro- 
tects within  a  limited  period  following  exposure. 
Immediate  vaccination  is  demanded  in  case  of 
exposure.  Healthy  infants  may  be  vaccinated 
within  the  first  six  weeks  or  two  months  of  life 
and  at  any  earlier  period  in  case  of  exposure. 
Immunity       An  attaclv  of  smallpox  confers  prolono^ed  and, 

and  Snscep-  ^  i  o  ^ 

tibiiity.  with  fcw  exccptious,  lasting  immunity.  Second 
and  even  third  attacks  have  been  described.  It  is 
known  that  those  who  have  had  smallpox  may  be- 
come susceptible  to  vaccination  after  a  period  of 
time.  Susceptibility  varies  a  good  deal  with  age. 
During  the  ages  of  from  two  to  fourteen  years 
the  disease  is  less  common  than  between  fifteen 
and  forty,  and  after  this  period  it  again  decreases 
in  frequency.  -Undoubted  instances  of  natural 
immunity  to  smallpox  occur,  but  they  are  very 
rare. 
Leucocytes.  Smallpox  is  accompauicd  b\  a  leucoc}i:osis 
which  is  peculiar  because  of  the  large  number  of 
mononuclears.  There  is  a  slight  rise  in  the 
number  of  leucocvtes  durinsj  the  first  febrile  on- 
set,  a  fall  to  almost  normal  during  the  remission, 
followed  by  a  second  rise,  which  may  be  as  high 
as  16,000  to  20,000.  Fatal  cases  show  a  terminal 
hypoleucocytosis  (Magrath,  Brinckerhoff  and  Ban- 
croft). Large  numbers  of  lymphocytes  are  also 
found  in  the  pustules  (Koger).  Nothing  of  a  sat- 
isfactory nature  is  known  concerning  the  relation- 
ship of  the  leucocytes  to  recovery  and  immunity. 
Serum.  There  is  no  serum  therapy  for  smallpox.  The 
interesting  observation  has  been  made,  however, 
that  the  serum  of  convalescents  or  of  vaccinated 


VARICELLA.  743 

man   or   animal   will,   when   mixed   with    vaccine 
virus,  prevent  its  action. 

Horsepox  is  identical  with  cowpox.  Sheeppox 
(clavel6e)  is  an  independent  disease.  The  virus  of  cow- 
pox  produces  a  local  lesion  in  the  sheep,  but  does  not 
cause  immunity  to  sheeppox.  The  virus  of  sheeppox,  on 
the  other  hand,  has  no  effect  on  horses  and  cattle 
(Nocard  and  Leclainche).  The  virus  of  sheeppox  is 
fi  1  terable    ( Borrel ) . 

VIII.    CHICKENPOX      (varicella). 

Although  the  skin  manifestations  of  varicella 
often  resemble  those  of  smallpox  to  such  an 
extent  that  differentiation  is  difficult,  the  two 
diseases  are  distinct.  Nothing  indicates  this  more 
clearly  than  the  fact  that  one  who  has  recovered 
from  varicella  is  susceptible  to  vaccination,  and  it 
is  Imov/n  further  that  an  attack  of  chickenpox 
does  not  protect  against  smallpox. 

The  etiology  is  unknown,  and  no  organism 
which  has  been  described  can  be  considered  the 
probable  cause. 

Varicella  occurs  epidemically  and  sporadically. 
The  virus  probably  exists  in  the  lesions  of  the 
skin  and  in  the  scales,  and  the  latter  may  be  the 
chief  source  of  contagion.  There  is  no  definite 
knowledge  concerning  the  resistance  of  the  virus, 
nor  its  distribution;  the  conclusion  is  justified, 
however,  that  it  exists  in  the  circulation  at  least 
in  an  early  stage  of  the  disease.  The  infection 
atrium  likewise  is  a  matter  of  conjecture,  but 
probably  is  to  be  found  in  the  lungs  or  upper 
respiratory  tract. 

The  patients  should  be  isolated  and  school  chil- 
dren should  not  be  allowed  to  return   to  school 


744  INFECTION     AND     IMMUNITY. 

until  desquamation  is  complete.  Disinfection 
should  be  practiced. 

Susceptibilit}^  and  virulence  would  seem  to  vary, 
since  the  severity  of  the  cutaneous  lesions  is  not 
constant.  In  delicate  and  tuberculous  children, 
the  lesions  may  become  gangrenous.  Hemorrhagic 
varicella  is  observed  occasionally.  Such  compli- 
cations as  nephritis  and  otitis  media  occur. 

Varicella  is  a  disease  of  childhood,  although  it 
may  occur  in  adults.  Infants  are  attacked  less 
frequently.  Second  or  even  third  attacks  occur, 
although  they  are  rare. 

There  is  no  serotherapy. 

IX.    SCARLET  FEVER. 

The  role  which  the  streptococcus  plays  in  scarlet 
fever  was  considered  on  page  527. 

The  "bodies"  recently  observed  by  Mallory  may 
be  referred  to  briefly. 
The  Proto-  In  1903  Mallory  described  certain  protozoon- 
^**>ikii*ory!  like  bodies  found  in  the  skin  of  four  cases.  They 
could  be  divided  into  two  groups,  one  of  which 
consisted  of  "round,  oval,  elongated,  lobulated 
bodies"  from  2  to  7  microns  in  diameter ;  the  indi- 
viduals of  the  second  group  "contain  a  central 
round  body,  around  which  are  grouped,  on  optical 
section,  from  10  to  18  narrow  segments,  which,  in 
some  cases,  are  united,  but  in  others  are  sharply 
separated  laterally  from  each  other."  They  occur 
within  and  between  the  epithelial  cells  and  in  the 
superficial  part  of  the  corium.  He  gives  the  name 
of  Cyclaster  scarlatinalis  to  these  bodies,  and,  al- 
though expressing  the  belief  that  they  are  protozoa 
and  have  a  causal  relation  to  scarlet  fever,  does  not 
claim  to  have  proved  such  a  relation. 


SCARLET     FEVER.  745 

Duval  corroborated  the  discovery  of  Mallory, 
and  demonstrated  the  bodies  in  five  out  of  eighteen 
cases  in  blisters  which  were  produced  artificially 
during  the  height  of  the  eruption.  Field  found 
them  not  only  in  the  skin  of  scarlet  fever^  but  also 
in  that  of  measles  and  concludes  that  many  of 
them  at  least  represent  artifacts  or  degeneration 
forms  of  tissue  cells.  More  extensive  observations 
seem  to  be  necessary  to  establish  the  nature  of 
these  supposed  parasites. 

Other  micro-organisms  which  have  been  de- 
scribed as  the  cause  of  scarlet  fever,  including  the 
Diplococcus  scarlatince  of  Class,  we  may  pass  over 
with  the  remark  that  the  claims  concerning  them 
have  not  been  upheld. 

The  contagiousness  of  scarlet  fever  is  extreme,  contagious- 
and  the  virus  undoubtedly  is  thrown  into  the  sur-  Transi^i^sion. 
rounding  air  from  the  skin  of  the  patient.  It  is 
highly  probable  that  the  virus  also  reaches  the  sur- 
rounding air  from  the  respiratory  passages  by 
means  of  "drop  infection,'^  since  transmission  may 
occur  before  the  skin  shows  involvement.  Patients 
continue  to  be  infectious  for  from  4  to  6  weeks  or 
longer  after  the  appearance  of  the  eruption.  The 
disease  may  be  transmitted  by  an  intermediate 
healthy  person,  or  by  contaminated  clothing  or 
furnishings.  The  origin  of  epidemics  from  milk 
which  has  in  some  way  been  contaminated  seems 
to  have  been  proved  in  a  number  of  instances. 

Of  great  importance  for  the  persistence  of  an 
epidemic  is  the  resistance  of  the  virus,  which  re- 
mains viable  and  virulent  for  months  and  possibly 
for  years,  when  under  suitable  conditions. 

Prophylaxis  demands  isolation  of  the  patients   Prophylaxis. 
until  desquamation  is  complete;  the  use  of  anti- 


740  INFECTION     AND     IMMUNITY. 

septic  baths  or  ointments,  or  vigorous  scrubbing 
with  soap  as  desquamation  proceeds;  antiseptic 
treatment  of  the  mouth  cavity;  disinfection  of  all 
utensils,  linen,  etc.,  with  which  the  patient  has 
been  in  contact ;  avoidance  of  stirring  up  the  dust 
in  the  room,  which  demands  moist  rather  than  dry 
cleansing;  the  disinfection  of  the  sputum  and 
other  discharges  of  the  patient;  an  abundance  of 
fresh  air  and  sunshine  in  the  sick  room;  the  final 
disinfection  of  the  room.  Physicians  and  nurses, 
when  in  the  presence  of  the  patient,  should  wear 
long  gowns,  which  can  be  discarded  on  leaving, 
and  other  well-known  precautions  should  be  ob- 
served to  avoid  spreading  of  the  disease.  The  pro- 
phylactic vaccination  by  means  of  streptococcus 
(Gabritchewsky)  is  deserving  of  further  trial. 
snscepti-       Scarlct  fcvcr  is  particularly  a  disease  of  child- 

toility   and    ,-,..-,  .  « 

immnnity.  hood,  'a  large  proportion  of  cases  occurring  before 
the  tenth  year"  (Osier).  Adults  are  attacked  not 
infrequently.  Infants  are  less  susceptible  than 
older  children.  Many  examples  of  family  immun- 
ity, which  probably  is  relative,  are  encountered, 
and  likewise  instances  in  which  there  is  a  family 
susceptibility.  In  a  given  family  examples  of  in- 
dividual immunity  and  susceptibility  are  fre- 
quently met  with.  One  attack  usually  confers  im- 
munity against  a  second,  but  not  invariably. 
Lencocytes.  Scarlatina  is  characterized  bv  a  leucocvtosis, 
the  degree  of  which  bears  some  relation  to  the 
severity  of  the  infection.  In  mild  cases  the  aver- 
age is  from  10,000  to  18,850  (Bowie),  in  moder- 
ately severe  cases  from  20,000  to  40,000,  or  even  as 
high  as  78,000  (Klotz)  ;  in  malignant  uncompli- 
cated cases  there  is  a  tendency  to  a  low  leucocyto- 


MEASLES.  747 

sis  (Klotz).  How  much  of  this  leucocytosis  de- 
pends on  co-existing  streptococcus  infection  re- 
mains uncertain. 

Treatment  with  antistreptococcus  eerum  is  the  seram 
only  serotherapeutic  measure  which  has  been  ad-  '*'*'«*'«>»'■• 
vocated  in  relation  to  scarlet  fever.  This  is  done 
either  on  the  assumption  that  the  disease  is  of 
streptococcus  etiology,  satisfactory  proof  of  which 
has  not  yet  been  obtained,  or  with  the  hope  that 
the  serum  will  influence  favorably  secondary  in- 
fections with  the  streptococcus.  The  serums  of 
A^ronson,  Moser  and  of  Menzer  have  been  tried 
more  than  others.  Moser  is  probably  more  enthu- 
siastic than  others,  and  he  claims  a  reduction  in 
the  mortality  from  an  average  of  13.08  per  cent, 
to  8.9  per  cent,  in  400  cases.  Others  have  observed 
a  favorable  influence  in  some  cases,  but  the  re- 
sults are  not  uniform.  The  development  of  sec- 
ondary streptococcus  infections  can  not  be  pre- 
vented by  the  use  of  the  serums,  although  it  is 
stated  that  their  severity  may  be  moderated. 

Of  theoretical  interest  is  the  report  by  Weiss- 
becker  and  by  v.  Leyden  that  the  serum  of  con- 
valescents causes  a  reduction  of  the  temperature 
and  a  shortening  of  the  course  of  the  disease. 

The  results  published  up  to  the  present  time 
indicate  that  we  have  not  as  yet  an  efficient  serum 
for  scarlet  fever  (see  also  p.  527). 

X.    MEASLES. 

Bacilli  which  have  been  recognized  in  the  con-  ^icro- 
junctiva,  sputum  and  nasal  passages  in  cases  of  «»-sranism«. 
measles  have,  for  the  most  part,  resembled  either 
the  diphtheria  or  the  influenza  bacillus.     Pseudo- 
diphtheria  bacilli  are  normal  residents  in  the  eye, 


748  IXFEGTION     AND     IMMUNITY. 

and  influenza-like  bacilli  are  found  in  the  sputum 
in  various  conditions;  hence,  there  is  insufficient 
reason  to  associate  such  organisms  with  the  etiol- 
ogy of  measles.  The  micrococci  found  by  Lasage 
(1900)  have  not  received  recognition  as  the  cause 
of  the  disease. 

Measles  is  highly  contagious,  even  during  the 
prodromal  stage.  The  contagion  doubtless  is  ex- 
creted from  the  lungs  as  well  as  the  skin,  and,  in 
view  of  the  early  bronchial  symptoms,  the  virus 
probably  gains  entrance  through  the  lungs.  Suc- 
cessful inoculation  into  man  with  blood  taken 
from  the  involved  skin  shows  that  the  virus  exists 
in  the  circulation  of  the  skin.  Hektoen  doubts 
the  decisiveness  of  a  number  of  these  experiments 
since  they  were  carried  out  in  the  presence  of 
epidemics  and  natural  infection  could  not  be  ex- 
cluded; at  the  same  time  he  does  not  question  the 
results  of  Mayr  (1852) .  In  two  experiments  on  man 
Hektoen  determined  the  presence  of  the  virus  in  the 
blood.  "The  results  of  these  two  experiments  per- 
mit the  conclusion  that  the  virus  of  measles  is 
present  in  the  blood  of  patients  with  typical 
measles  some  time  at  least  during  the  first  30 
hours  of  the  eruption ;  furthermore,  that  the  virus 
retains  its  virulence  for  at  least  24  hours  when 
such  blood  is  inoculated  into  ascites-broth  and  kept 
at  37°  C.  This  demonstration  shows  that  it  is 
not  difficult  to  obtain  the  virus  of  measles  unmixed 
with  other  microbes  and  in  such  form  that  it  may 
be  studied  by  various  methods."  The  virus  is 
much  less  resistant  than  that  of  scarlet  fever.  The 
varying  grades  of  severity  of  different  epidemics 
show  that  it  is  subject  to  alteration  in  its  virulence. 


MEASLES. 


749 


Although  measles  is  considered  somewhat  harm- 
less on  the  whole,  dangerous  complications,  such 
as  broncho-pneumonia  and  otitis  media,  are  suffi- 
ciently frequent.  The  development  of  tuberculosis 
following  measles,  an  event  which  is  not  uncom- 
mon, shows  that  measles  may  greatly  decrease  gen- 
eral resistance. 

The  prophjdaxis  of  measles  is  not  different  from 
that  of  other  exanthemata.  The  isolation  should 
continue  for  four  weeks  after  the  appearance  of  the 
exanthem  (Gotschlich).  The  sickroom  should  be 
disinfected  eventually.  The  view  not  uncommonly 
encountered  that  measles  is  a  good  thing-  for  a 
child  to  have  and  be  over  with  is  in  no  way  Justifi- 
able. The  development  of  serious  complications 
can  in  no  case  be  foreseen,  and  fatalities  may  occur 
even  in  mild  epidemics. 

Very  young  children,  the  rachitic  and  tubercu- 
lous, and  those  in  a  poor  state  of  nutrition  should 
be  guarded  against  exposure,  for  in  them  measles 
is  often  malignant.  Infants  are  less  susceptible 
than  older  children.  Measles  occurs  in  adults  more 
frequently  than  scarlet  fever.  Eecurrences,  on  the 
whole,  are  frequent,  as  many  as  four  attacks  hav- 
ing been  noted  in  an  individual.  Hence,  the  im- 
munity caused  by  infection  is  not  uniformly  of  a 
permanent  character. 

It  is  very  probable  that  the  inhabitants  of  a 
country  in  which  measles  is  endemic  gradually 
become  immunized,  with  the  result  that  the  disease 
prevails  in  a  mild  form.  On  the  contrary,  regions 
in  which  measles  has  hitherto  been  unknown,  or"' 
has  been  absent  for  many  decades,  are  susceptible' 
to    visitations    of   great    malignancy.      Such   epi*' 


Effect   on 
Resistance. 


Prophylaxis. 


Suscepti- 
bility  nnd 
Reenrrence. 


Racial 

Iiuninniza- 

tion. 


750  INFECTION     AND     IMMUNITY. 

demies  have  occurred  in  the  Faroe  Islands  and  in 
Iceland,  with  a  mortality  exceeded  by  few  epi- 
demic diseases. 
LeacocFtes.  A  moderate  leucocytosis  is  excited  in  measles, 
"which  begins  soon  after  infection,  reaches  its 
maximum  six  days  before  the  appearance  of  the 
eruption,  and  lasts  into  the  first  part  of  the  stage 
of  invasion"  (Tiliston).  We  are  ignorant  of  the 
significance  of  this  leucoovtosis. 

There  is  no  serum  therapy  for  measles.  Weiss- 
becker  states  that  the  serum  of  convalescents  in- 
fluences the  course  of  the  disease  favorably. 

XI.    GERMAN   MEASL'ES    (ROTHELN). 

Rotheln  is  considered  as  distinct  from  measles, 
in  spite  of  clinical  similarities.  It  is  recognized 
because  of  certain  peculiarities  in  the  eruption  and 
its  uniformly  mild  course.  Perhaps  the  strongest 
reason  for  believing  the  two  diseases  to  be  distinct 
lies  in  the  fact  that  an  attack  of  rotheln  does  not 
leave  an  immunity  against  measles. 

Eotheln  is  contagious.  Efforts  should  be  made 
to  prevent  extension,  as  in  measles,  the  methods  of 
transmission  being  the  same  in  the  two  diseases. 

XII.    WHOOPING  COUGH. 

Various  protozoa  (?)  and  bacteria  (cocci  and 
bacilli)  have  been  assigned  as  the  cause  of  whoop- 
ing cough.  Many  of  the  so-called  protozoa  found 
in  the  throat  were  undoubtedly  tissue  cells  (leuco- 
cytes, ciliated  epithelium).  Among  the  cocci,  the 
diplococcus  of  Ritter  (1892)  acquired  some  promi- 
nence. He  is  said  to  have  found  it  constantly  in 
146  cases.  Investigations  by  others  failed  to  jus- 
tify his  conclusions. 


PERTUSSIS. 


751 


Disregarding  some  other  bacilli  which  certain 
investigators  have  attempted  to  bring  into  rela- 
tion with  pertussis^  we  may  note  the  essential  facts 
concerning  an  influenza-like  bacillus  which  has 
been  found  with  great  constancy  and  by  many 
competent  investigators  in  the  sputum  of  patients. 
First  observed  by  Sprengler  (1897)  in  pertussis 
sputum,  this  organism  or  bacilli  similar  to  it  have 
been  found  by  Czaplewski  and  Hensel,  Zusch, 
Cavasse,  Vincenzi,  Elmassian,  Luzzatto,  Arnheim, 
Jochmann  and  Kruse,  Eeyher,  Smit.  Wollstein, 
and  Davis.  The  organism  is  said  to  be  somewhat 
larger  and  thicker  than  the  true  iniiuenza  bacillus, 
but  has  the  same  bipolar  staining  affinity  and  the 
same  demand  for  hemoglobin  for  its  growth  in 
pure  cultures.  There  is  some  difference  of  opinion 
as  to  whether  the  organisms  described  by  these 
different  observers  are  all  identical  and  as  to 
whether  all  have  worked  with  pure  cultures.  The 
conclusion  of  Davis  would  seem  to  sum  up  the 
situation:  ''With  the  exception  of  Manicatide, 
probably  all  of  the  investigators,  at  least  in  more 
recent  years,  have  been  dealing,  either  in  pure  or 
impure  cultures,  with  the  influenza-like  bacillus, 
first  described  by  Sprengler  and  later  by  Joch- 
mann." Culturally  they  are  not  to  be  differen- 
tiated from  the  influenza  bacillus.  When  in  pure 
culture  they  demand  hemoglobin  for  their  develop- 
ment, although  the  amount  of  hemoglobin  may  be 
so  small  as  not  to  color  the  medium.  When  in 
mixed  culture  with  the  streptococcus,  staphylo- 
coccus, pneumococcus  and  B.  xerosis,  they  grow 
abundantly  even  in  the  absence  of  hemoglobin. 
Hence,  in  relation  to  symbiosis,  also  they  resemble 
the  influenza  bacillus.    For  symbiotic  development 


The    Inila- 
enzu-lilve 
BiicillaM    of 
Sprengler 
uiid    of 
Jocliinaiiii. 


Heiuophllic 
Properties 
and   Sym- 
biosis. 


752  INFECTION     AND     IMMUNITY. 

it  is  necessary  that  the  secondary  organisms  be 
living;  when  killed  or  when  the  filtrates  of  bouil- 
lon cultures  are  used,  the  ^'pertussis  bacilli"  are 
not  stimulated  to  growth. 
Pathogen-  Inoculatiou  of  pure  cultures  on  the  mucous 
membrane  of  the  upper  respiratory  passages  in 
various  animals,  including  the  monkey,  does  not 
produce  a  pertussis-like  infection.  The  organisms 
have,  however,  a  low  degree  of  virulence  for  ani- 
mals, particularly  the  guinea-pig.  Davis  found 
that  three  blood-agar  cultures  injected  intraperi- 
toneally  killed  guinea-pigs  in  24  hours  or  less. 
The  virulence  of  the  organism  is  augmented  when 
mixed  with  certain  other  bacteria.  By  injecting  it, 
mixed  with  a  non-pathogenic  staphylococcus,  its 
virulence,  after  six  passages,  was  so  increased  that 
one  blood-agar  culture  killed  guinea-pigs  in  24 
hours  (Davis).  In  this  respect,  also,  it  resembles 
the  influenza  bacillus. 
sigrnificnni-e.  Inoculated  in  the  throat  of  an  adult,  who  pre- 
sumedly had  never  had  whooping  cough,  a  distinct 
febrile  reaction,  lasting  two  or  three  days,  devel- 
oped after  an  incubation  period  of  two  days 
(Davis).  Headache  and  pharyngitis  were  accom- 
paniments of  the  reaction  and  the  phar}Tigitis 
continued  for  at  least  four  weeks.  There  was  lit- 
tle cough,  and  it  was  concluded  that  the  micro- 
organism had  not  produced  whooping  cough, 
although  it  had  shown  toxic  and  infec- 
tious properties.  The  bacillus  proliferated  enor- 
mously in  the  pharynx  and  nose  and  was  still  to 
be  cultivated  after  four  weeks.  Such  an  organism 
may  well  be  an  important  factor  in  whooping 
cough,  even  though  it  is  not  the  essential  cause. 
Davis  is  inclined  to  regard  its  relation  to  whoop- 


PERTUSSIS.  763 

ing  cough  as  similar  to  that  of  the  streptococcus 
to  scarlet  fever — i.  e.,  a  very  important  compli- 
cating organism. 

Davis  finds  still  further  reason  for  doubting  its 
specific  relationship  to  whooping  cough  from  the 
fact  that  it  was  found  frequently  in  measles,  acute 
influenza,  epidemic  meningitis,  bronchitis,  vari- 
cella and  in  normal  throats. 

In  1906  Bordet  and  Gengou  isolated  a  bacillus  Baciiius  of 
from  cases  of  whooping  cough  and  gave  the  fol-  oeng-ou^"** 
lowing  reasons  for  believing  that  it  was  the  spe- 
cific etiologic  factor  in  this  disease:  1.  The  organ- 
ism is  found  in  overwhelming  numbers  during  the 
early  course  of  the  disease  and  in  almost  pure  cul- 
ture. 2.  The  bacilli  as  antigen  give  a  comple- 
ment-fixation reaction  with  the  serum  of  pertussis 
patients  and  this  reaction  does  not  occur  with 
other  bacteria  associated  with  the  disease. 

The  organism  is  a  short,  polar-staining  ovoid 
resembling  the  influenza  bacillus  but  slightly  lar- 
ger. Bordet  and  Gengou  grew  the  organisms  on  a 
culture  medium  made  up  of  a  glycerin-potatoe- 
blood-agar  mixture.  On  this  medium  the  organ- 
ism grows  in  the  form  of  a  delicate  film  made  up 
of  very  small  colonies  and  changes  the  medium  to 
a  dark  brownish  color. 

Wollstein  was  able  to  confirm  the  finding  of 
the  bacillus  in  the  early  stages  of  pertussis,  but 
failed  to  obtain  the  complement-deviation  reac- 
tion. Agglutination  was  very  irregular  and  no 
immune  opsonins  were  found.  The  etiologic  rela- 
tionship of  the  organism  to  whooping  cough  is  at 
present  uncertain. 

The   organism   is   disseminated    extensively   by 
coughing,  and  the  same  is  probably  true  of  the  es- 


754  INFECTION     AND     IMMUNITY. 

contag-ions-  sential  virus.  Close  contact,  as  by  kissing,  or  the 
"****  common  use  of  eating  utensils  is  a  means  of  trans- 
mission. The  opinion  has  been  advanced  by  Weill 
and  Pehn  that  pertussis  is  contagious  only  during 
the  catarrhal  stage  of  the  disease.  *'0f  ninety- 
three  non-immune  children  who  were  placed  with 
fifteen  children  who  were  in  the  convulsive  stage, 
none  became  sick^^  (cited  by  Gotschlich).  This 
point  is  not  sufficiently  established,  however,  to 
warrant  modifications  of  prophylactic  measures. 
Whooping  cough  is  often  epidemic  and  is  more 
common  in  cities  where  contact  with  the  infected 
is  more  likely  to  occur  than  in  the  country.  The 
incubation  period  is  from  seven  to  fourteen  days. 

Isolation  is  more  difficult  than  in  the  more  acute 
contagious  diseases,  yet  contact  with  other  chil- 
dren should  be  avoided  as  much  as  possible,  and 
the  patients  should  be  withdrawn  from  school 
until  recovery  is  complete. 

Pertussis  is  almost  exclusively  a  disease  of  chil- 
dren, although  older  people  may  be  attacked.  Sus- 
ceptibility is  not  general.  One  attack  usually  con- 
fers immunity.  A  varying  degree  of  leucocytosia 
is  excited  by  the  infection  (12,000  to  45,000).  the 
significance  of  which  is  not  known.  It  is  chiefly 
mononuclear. 

Serotherapy.  Serotherapy  for  whooping  cough  has  not  ad- 
vanced to  a  point  where  we  can  speak  with  as- 
surance concerning  it.  Manicatide  (1903)  im- 
munized horses  and  sheep  with  the  organism  which 
he  cultivated  from  a  large  number  of  cases.  He 
reports  that  cure  may  be  accomplished  in  from 
two  to  twelve  days  when  the  serum  is  used  within 
the  first  fifteen  days  of  the  disease.  The  bacillus  of 
Manicatide  differs  from  the  influenza-like  organ- 


MUMPi^.  755 

isni  of  other  observers,  hence,  his  antiserum  can 
not  be  accepted  unreservedly  as  a  specific  serum 
for  whooping  cough.  Smit  found  that  an  anti- 
serum for  the  influenza-like  organism  exerted  no 
influence  on  the  disease.  Bordet  found  the  serum 
of  a  horse  immunized  to  his  bacillus  of  question- 
able curative  value. 

XIII.    MUMPS    (epidemic  PAROTITIS). 

Mumps  occurs  epidemically  in  children,  particu- 
larly in  schools,  in  other  institutions,  and  in  sol- 
diers confined  to  barracks.  It  is  most  frequent  in 
the  spring  and  autumn  and  probably  is  endemic  in 
large  centers  of  population.  It  is  contagious,  the 
virus  probably  being  disseminated  from  the  upper 
respiratory  passages  with  infected  droplets  of  spu- 
tum and  saliva.  The  disease  has  an  incubation 
period  of  two  to  three  weeks  and  runs  its  course 
in  from  seven  to  ten  days. 

Involvement  of  the  testis,  ovary  or  female  breast 
are  complications  to  be  feared  in  adult  life ;  ^^orchi- 
tis,  albuminuria,  with  convulsions,  acute  uremia, 
endocarditis  and  peripheral  neuritis  are  occasional 
complications"  (Osier).  Fatal  meningitis  devel- 
ops rarely.  Very  young  infants  and  adults  are  at- 
tacked less  frequently  than  children  of  school  age. 

In  1893,  Laveran  and  Catrin  described  a  diplo-  Dipiococci 
coccus  obtained  by  aspiration  of  the  exudate  in  the  *"  ^i«mps. 
parotid  gland.  The  organism  was  also  isolated 
from  the  testicle  in  orchitis  cases  and  from  the 
circulating  blood.  Since  that  time,  diplococci 
have  been  isolated  from  cases  of  mumps  by  a  num- 
ber of  observers.  In  1909,  Herb  isolated  a  diplo- 
coccus  which  she  considers  as  probably  identical 
with  the  organisms  described  by  previous  writers. 


756 


INFECTION     AND     IMMUNITY. 


Patliosen- 
icity. 


Immunity. 


The  organism  was  cultivated  at  autopsy  from 
the  lung,  testicle,  cerebrospinal  fluid,  bile,  parotid 
gland  and  pericardial  fluid.  The  coccus  is  a 
Gram-positive  organism  occurring  mostly  in  pairs 
but  also  in  short  chains  and  small  groups.  It 
varies  from  0.5  to  0.8  microns  in  diameter  in 
twenty-four-hour  cultures.  It  is  non-motile,  has 
no  capsule,  and  forms  no  gas  or  indol.  It  grows 
slowly  on  ordinary  media  and  much  more  rapidly 
on  media  containing  saliva.  The  growth  on  saliva 
agar  appears  as  pearly  white  pin-point  discrete 
colonies. 

The  organism  is  fatal  to  white  mice,  w^hite  rats, 
guinea-pigs  and  rabbits  when  injected  subcutan- 
eousl}";  when  injected  into  Steno's  duct  in  mon- 
keys and  dogs  non-suppurative  parotitis  was  pro- 
duced and  occasionally  an  orchitis.  The  evidence 
indicates  strongly  that  the  diplococcus  described 
by  Herb  is  the  specific  etiologic  factor  in  mumps. 

One  attack  usually  establishes  protection.  Ac- 
cording to  Herb,  the  opsonins  would  seem  to  play 
an  important  part  in  the  protection  of  the  body 
against  mumps. 

Patients  should  be  isolated  for  three  weeks 
from  the  time  symptoms  appear. 


XIV.    EPIDEMIC  POLIOMYELITIS. 

Epidemic  poliomyelitis,  or  acute  anterior  mye- 
litis, is  an  acute  febrile  disease  of  children  and 
young  adults  accompanied  by  an  acute  inflamma- 
tion of  the  cord  and  brain.  Clinically,  it  is  char- 
acterized by  paralysis  of  various  muscles,  usually 
those  of  the  extremities.  The  paralysis  is  very 
rapid  in  onset  and  varies  in  tendency  to  recovery 
and  permanent  disability. 


rOLIOMYELIim. 


757 


Micro- 
oreanisnis. 


The  disease  has  been  known  for  over  half  a  cen- 
tury, but  it  has  been  recognized  as  an  infectious 
disease  for  only  a  few  years. 

Although  various  bacteria  have  been  described 
in  connection  with  the  disease,  there  has  been  little 
reason  for  considering  them  other  than  mixed  in- 
fections or  contaminations. 

Flexner  and  Lewis  found  that  the  virus  of 
poliomyelitis  is  filterable  and  describe  very  minute 
bodies  occurring  in  the  infectious  filtrate.  The 
bodies  can  be  stained  with  Loeffler's  flagella  stain 
and  cause  a  cloudiness  in  culture  media  after  suit- 
able incubation.  The  transfer  of  a  small  amount 
of  such  cloudy  media  to  a  second  clear  media  re- 
sults again  in  cloudiness  after  incubation.  The 
virus  loses  its  virulence  when  heated  to  from  45° 
to  50°  C.  for  half  an  hour,  but  resists  freezing. 

Landsteiner  and  Popper,  in  1909,  and  Knopf el- 
macher  a  little  later,  succeeded  in  producing  polio- 
myelitis in  monkeys  by  injection  of  emulsified 
cords  of  children  dying  of  the  disease.  They  were 
unable  to  infect  second  animals  with  material 
from  the  first.  Later,  in  1909,  Flexner  and  Lewis 
were  able  to  produce  poliomyelitis  in  monkeys  in 
a  way  similar  to  that  described  by  Landsteiner 
and  Popper,  and  succeeded  in  transmitting  the 
disease  from  one  monkey  to  another. 

Infection  may  be  produced  in  monkeys  by  in- 
jecting the  virus  into  the  brain,  spinal  canal  sub- 
cutaneous tissue,  peritoneal  cavity  or  into  the  large 
nerves. 

Experimental  poliomyelitis  can  be  produced  bv  Distribntion 

M         .     .        .  (,  „  *^     of  the  Vims 

XAQ  injection  of  material  from  the  blood  at  the 
beginning   of   the   infection   and  by   injection   of 


Experinieutal 
Poliomyelitis. 


758  INFECTION     AND     IMMUNITY. 

emulsions  from  the  nasopharyngeal  mucous  mem- 
brane. The  emulsions  of  central  nervous  tissues 
give  the  most  constant  results,  while  the  emul- 
sions of  other  organs  such  as  liver,  spleen  and 
bone  marrow  have  failed  to  give  results.  It  is 
possible  that  infection  takes  place  in  a  manner 
similar  to  the  process  in  epidemic  meningitis. 
That  is  by  dissemination  of  droplets  and  particles 
from  the  nasopharyngeal  membrane. 

In  a  reinoculation  of  ten  monkeys  which  had 
recovered  from  poliomyelitis,  Flexner  and  Lewis 
observed  no  instances  of  second  attacks.  In  nor- 
mal monkeys  72  per  cent,  of  those  inoculated  be- 
came infected  and  showed  paralysis.  Those  which 
did  not  become  paralyzed  were  suspected  of  mild 
attacks.  It  is  possible  that  vaccination  may  be 
successful. 

XV.    NOMA. 

Noma,  or  gangrenous  stomatitis,  is  a  somewhat 
rare  disease  of  children  whose  resistance  is  low- 
ered by  the  acute  infectious  diseases.  Among  these 
it  is  found  most  frequently  associated  with  meas- 
les. Next  to  measles,  it  is  oftenest  found  in 
typhoid,  intermittent  fever  mercurialism,  scarlet 
fever,  pertussis,  enteritis,  variola  and  many  other 
diseases. 
FnMifoi-m       Perthes,  Seiffert,  Matzenaur  and  others  found 

Bncilli    and  n       -n  ^^^^  t  •      n 

spiriiiii.  associated  with  noma,  fusiform  bacilli  and  spirilla. 
These  observations  have  since  been  confirmed  by 
many  others.  The  organisms  are  found  in  the 
necrotic  tissues  and  especially  at  the  line  of  ad- 
vancing necrosis.  Ellerman,  in  1904,  cultivated 
fusiform  bacilli  from  a  case  of  noma.  Weaver 
and  Tunnicliff  obtained  pure  cultures  of  fusiform 


NOMA.  75U 

bacilli  from  noma  in  1905.  'J'lic  organism  is  an 
obligative  anaerobe  requiring  a  temperature  of 
about  37°  C.  for  growth.  The  presence  of  blood 
serum  or  ascites  fluid  is  necessary  for  obtaining 
the  best  growth,  but  cultures  can  be  obtained  on 
glycerin  agar.    All  cultures  have  a  foul  odor. 

On  ascites  agar  the  bacilli  occur  as  delicate 
pointed  Gram-negative  rods.  In  ascites  broth  the 
organisms  are  more  slender,  not  so  pointed,  and 
tend  to  form  chains.  On  solid  media  wavy  fila- 
ments are  found.  In  old  cultures  forms  similar 
to  the  spirilla  found  in  the  tissues  were  found. 
Tunnicliff  isolated  from  the  gums  of  healthy  sub- 
jects, fusiform  bacilli  which  were  apparently  iden- 
tical in  cultural  characteristics  and  morphology 
with  those  found  in  noma.  In  pure  cultures 
grown  several  days  spirilla  were  found  rather  con- 
stantly and  it  would  seem  as  if  the  spirilla  were 
simply  a  stage  in  the  development  of  the  fusiform 
bacilli. 

The  number  of  cases  in  which  the  bacilli  and 
spirilla  have  been  found  associated  with  noma 
makes  it  strongly  probable  that  they  are  the  cause 
of  the  disease. 

Fusiform  bacilli  and  spirilla  similar  to  those 
isolated  from  noma  have  been  found  in  ulcero- 
membranous angina  and  stomatitis,  in  hospital 
gangrene  and  in  fetid  infections  in  various  parts 
of  the  bodv. 


INDEX 

PAGE 

Abrin     21,  218 

Achalme,   bacillus   of,    in   rheumatic   fever 525 

Acne,    staphylococcus    in 543 

Acquired  Immunity   (see  Immunity,  acquired). 
Active  immunity    (see   Immunity,  active). 

Actinomyces   hovis   ct  liominis    (ray   fungus) 25.  G29 

Classification  of,  630,  631  ;  cultivation  and  morphol- 
ogy of,  630 ;  lungs  in,  502 ;  occurrence  of,  in  Na- 
ture, 631  ;  resistance  of,  630  ;  species  of,  and  viru- 
lence  of,  631. 

Actinomycosis    25,    620,  633 

Animals,  susceptibility  of,  to,  629  ;  fibrous  tissue 
formation  in,  629,  632;  immunity  and  susceptibil- 
ity to,  632  ;  infection  atria,  631  ;  iodid  of  potassium 
in,  633  ;  lesions,  character  of,  632  ;  phagocytosis  in, 
632  ;  prophylaxis  of,  632  ;  transmission  of.  631. 
Acute   articular    rheumatism    (see    Rheumatic   fever)  . .-.    729 

Adrenal   gland,   cytotoxin   for 304 

Agglutination     206,  219 

Of  erythrocytes,  218  ;  of  erythrocytes  with  silicic  acid, 
244  ;  etiology,  determined  by,  23  ;  group  agglutina- 
tion, 224,  227 :  immunity,  relation  to,  207.  208  ; 
macroscopic  and  microscopic,  216,  217  ;  prognostic 
importance  of.  209 ;  sodium  chlorid,  influence  on, 
224 :  stages  in  the  reaction,  224 ;  substances  con- 
cerned, 216  :  serum  dilutions,  227  ;  specificity.  225  ; 
technic,  212 ;  theories  of  mechanism  of,  230 ;  see 
also  under  Agglutinins  and  under  different  diseases 
and  micro-organisms. 

Agglutinins     206-218 

Absorption  of  by  bacteria,  347 ;  agglutinophorous 
group,  222  ;  auto-agglutinins,  218  ;  chief  agglutinins, 
225  :  congenital,  207,  210 ;  definition.  219 ;  distri- 
bution of.  in  the  body,  210  ;  Ehrlich's  theory  of  the 
production  of,  228 ;  ferments,  action  of,  on,  210, 
221  ;  formation  of,  following  vaccination.  377  ; 
haptophorous  group  of,  222  ;  Uauptagglutinin,  225  ; 
immune,  174,  207  ;  isoagglutinins.  218  ;  mixed  infec- 
tions, influence  of,  on.  227  ;  Mitagfihitinin,  223 ; 
normal,  223 :  origin  of,  210 ;  precipitation  of,  by 
chemicals,  221  ;  production  of.  207 ;  receptors  of 
second  order,  222  ;  resistance  to  acids  and  alkalies, 
223  ;  resistance  to  heat,  211,  222.  223  ;  somatic  and 
flagellar,  221  ;  specificity  of,  200  ;  structure  of.  222  : 
union  with  cells,  character  of,  347,  348 ;  unit  of 
measure  of,  217;  variations  of.  in  animals,  228; 
variations  in  the  quantity  of,  209  ;  zvmotoxic  group 
of,  222 ;  see  Agglutination,  Agglutinogens,  Agglu- 
tinoids,  and  also  under  the  different  micro-organ- 
isms. 
Agglutinogcnic   power   of   bacteria 208 


762  1^'DEX. 

PAGE 

Agglutinogens,    or    agglutinable    substances 210 

Diffusibility  of,  221  ;  distribution  of.  220 ;  flagellar 
and  somatic,  221  ;  multiplicity  of.  221  ;  resistance 
of,  to  heat.  221  ;  structure  of.  222  ;  see  Agglutinins 
and  Agglutination. 

Agglutinoids    223 

Aggressins    122,  336 

Allergy    (see   Anaphylaxis). 

Alexins    150,   245 

Definition  of,  150  ;  identity  of.  with  complement.  249, 
250  ;  nature  and  .selective  action  of,  246  ;  see  Com- 
plement. 

Alkaloids. 

Failure  to  cause  formation  of  antibodies,  342  ;  state 
of,   within   the   cells.   342,   340. 

Amboceptoid    353 

Amboceptors     249,  256 

Absorption  of,  by  cells,  259.  261,  347;  bacteriolytic, 
258  ;  complementophilous  haptophore  of,  147  ;  cyto- 
philous  haptophore  of.  262 ;  formation  of.  264  ; 
formation  following  vaccination,  378 ;  hemolytic 
256 ;  influence  in  phagocytosis,  320 ;  isolation  of, 
260 ;   manner   of   action   of   with   complement.    260 ; 

262.  351,  352  ;  occurrence  of,  in  animal  secretions. 
274 ;  origin  from  leucocytes,  313.  320 ;  origin  in 
cholera.  320 ;  receptors  of  the  third  order.  351  ; 
sensitization  by.  256.  257,  259 ;  solutions  of,  258 ; 
specificity  of.  266,  267  ;  structure  of,  262  ;  svnonyms 
for,    262,    361  :    union    with    cells,    nature    of,    262, 

263.  347,  348:  see  Hemolysins  (serum).  Bacterio- 
lysins.  Cytotoxins  and   Venoms. 

Ameha  coU. 

Discovery  of.  686 ;  pathogenicity  of.  688  ;  symbiosis 
of,   687,   688  ;  see  Amebic  dysentery. 

Ameha    lyroteus     686 

Ameba. 

Cultivation  and  distribution  of.  687  ;  phagocytic 
action  of,  306  ;  resistance  of,  687 ;  symbiosis.  687, 
688. 

Amebic    dysentery    686 

Anatomic  changes  in.  680 :  immunity  to,  690  ;  liver 
abscess  in,  689 ;  occurrence  of,  689 ;  prophylaxis, 
689;  see  Amebae.  and  Ameha  colt. 

Amibodiasta.se     306 

Amyloid  degeneration,  production  of,  by  staphylococcus.    542 

Anaphylaxis. 

Acquired,  384;  active,  384;  anaphylactic  shock,  392; 
anaphylotoxin.  390 ;  antianaphylactic  state,  393 ; 
antibody  in,  388  ;  antigen  in,  385  ;  complement  in, 
390  ;  natural,  384  ;  passive,  384  ;  relation  to  revac- 
cination,  381  ;  i-elation  to  primary  toxicity,  386 ; 
relation  to  tuberculin,  395  ;  relation  to  serum  dis- 
ease. 396  ;  sensitization  in,  386  ;   theories  of,  391. 

"Anatomic   tubercle"    (see  Tuberculosis). 

Animals,   susceptibility   of,   to. 

Actinomycosis.  631  ;  anthrax.  494.  495  ;  B.  influenza', 
565  ;  Ji.  melitensis,  500  ;  cholera,  474  ;  hydrophobia, 
704,  705 ;  leprosy,  618  ;  Micrococcus  catarrhalis, 
551  ;  Micrococcus  meninf/itidis,  558  ;  oidiomycosis, 
639,  640 ;  pneumococcus,  504 ;  pseudotuberculosis, 
614  ;  relapsing  fever.  643  ;  staphylococcus,  375,  376  : 
streptococcus.  543  ;  sypliiiis,  648,  649;  trypanosomi- 


INDEX.  763 

PAGK 

asis,  G70,  080.  (581,  G82  ;  tuberculin,  581  ;  tuberculo- 
sis,   593,    594,    t)ll,    612. 

Animal  experiments,  in  testing-  value  of  serums o45 

Anopheles  mosquitoes. 

.1.  macmtipennis,  604,  665;  A.  unctipennis,  664;  habits 
of,  664.  665  ;  life  cycle  of.  665.  666  ;  malaria,  role 
in,   654  ;   migration   of,   666  ;   occurrence,   664. 

Anthracase-Immunprotciden     497 

Anthrax     492,   498 

Animals,  immunity  and  susceptibility  of,  495.  496 ; 
bacillemia.  493  ;  discovery  of  its  microbic  nature, 
4.  5.  6  ;  immunit.v,  496  ;  immunization,  mixed.  498  ; 
influence  of  streptococcus  on,  528  ;  malignant  pus- 
tule, 494  ;  occurrence,  492  ;  opsonins,  497.  498  ; 
phagocytosis  in.  316,  496 ;  prophylaxis,  495  ;  sero- 
therapy, 497  ;  toxic  results,  495  ;  transmission.  494  ; 
vaccination,  5,  6,  497 ;  wool-sorters'  disease,  495 ; 
see  also  B.  anthracis. 

Antiabrin     203 

Antiaggressins     338 

Antiamboceptors 270 

Danger  in  formation  of,  272  ;  as  receptors  of  the  first 
order,  351. 

Antibacterial   serums    (see   Bacteriolysins) 370-375 

Antibodies. 

Mechanism  of  production.  343 ;  origin  of.  354.  480 ; 
scheme  of,  360  ;  specificity  of.  352  ;  union  with  anti- 
gens, 344 ;  see  Antitoxins.  Amboceptors.  Agglutin- 
ins, Precipitins.  Hemolysins,  Bacteriolysins  and 
Cytotoxins. 

Anticomplements     269,   280,   351 

Anticrotin    203 

Anticytotoxins      295,   361 

Antiferments    175,   204 

Antigen  of  Wassermann  test 287 

Antigens. 

Scheme  of,  360  ;  union  with  tissue  cells,  character 
of.   344. 

Antiglobulin     239 

Anti-immune  serum    270 

Antilaccase    204 

Antileucocidin    203,  539 

Antileucotoxic   serum    299 

Antinephrotoxin    300 

Antineurotoxin    301 

For  venom,   430. 

Antipepsin     204 

Antiprecipitins    238 

Antirennet     204 

Antiricin    203,  345.   346 

Antirobin    203 

Antispermotoxin    296 

Autistaphylolysin    547 

Antisteapsin    204 

Antistreptocolvsin 519 

Antitoxins     .  .' 167.   204.   365.   398 

Earlv  administration  of.  367.  368  ;  curative  action  of. 
366.  367  ;  discovery  of.  10  ;  examination  of  by  F.  S. 
Hvgienic  Laboratorv.  188  ;  for  animal  toxins,  203  ; 
for  B.  hotulinis,  525;  for  B.  flipJith crier,  404.  406; 
for  B.  pyociianeHs,  424;  for  B.  tetani.  367,  416; 
for  bacterial  toxins,  203;  for  plant  toxins  (abrin. 
crotin,    ricin,    robin,   phallin).    203.    427;    for   pollen 


7G4  IXDEX. 

PAGE 

toxin,  4'2(> ;  lor  zootoxins.  431  ;  formation  of,  198  ; 
haptophorous  group  of,  192  ;  infections  characterized 
by  formation  of,  398,  431  ;  leucocytic  origin,  ques- 
tion of.  321;  manufacture  of,  180;  mode  of  action 
of,  345.  365,  370  ;  nature  of,  321  ;  toxins,  neu- 
tralization of,  by,  191.  345,  346 ;  normal,  147  ; 
preservation  of,  182,  184 ;  prophylactic  action  of, 
370  ;  receptors,  free.  202  ;  receptors  of  the  first 
order.  351  ;  relation  of.  to  toxins,  in  the  body,  366  ; 
relation  of.  to  toxins,  in  vitro,  365  ;  standardization 
of,  183,  419;  unit  of.  183;  see  Part  II,  Group  I,  and 
also  the  different  micro-organisms. 

Antitrypsin     204 

Antiurease     204 

Antivenin     181,  203,  431 

Antityrosinase     204 

Arachuolysin     (spider     poison) 204 

Arrhenius  and   Madsen.  views  of 354 

Arthritis     509,  514,   520,  545,  553,  559 

Arthus'    phenomenon    383 

Aspergillus      21,  641 

Atrophy,    phagocytosis    in 308,   309 

Attenuation. 

Importance   of   in   vaccination.    160 ;    methods  of,    363. 

Auto-agglutinins     218 

Autocytotoxins     293,  305 

Autolytic   products,   vaccination   with 364,  477 

Autonephrotoxins     299 

Autoprecipitins     236 

Autospermotoxin     296 

Bacillus   aiirogenes    capsulatus 29,  525 

Bacillus  alcaUgencs   434 

Bacillus    anthracis     25,  492,494 

Antagonism  of.  bv  other  bacteria,  494  ;  antiserums 
for,  9  ;  attenuation  of,  100,  363  ;  cultivation  of.  494  ; 
discovery  of.  4,  493 ;  gastric  .iuice,  effect  of,  on, 
141,  494 ;  immunity,  active,  497 ;  immunity,  ac- 
quired, 316.  496 :  immunity,  natural.  490 ;  immu- 
nity, passive,  497 ;  infection  atria,  141  :  opsonins, 
497  ;  phagocytosis  of.  496 ;  serums,  effect  of,  on, 
496 ;  spores  of.  6.  493 ;  toxic  properties  of.  495 ; 
virulence  of.  494  ;  see  Anthrax. 

Bacillus    hotulinus     419,  420 

Animals,  susceptibility  of,  421,  422 ;  antitoxin  for, 
422 ;  morphology,  etc.,  420 ;  occurrence  in  meat, 
420 ;  saprophytic  nature  of,  421  ;  spores  of,  420 ; 
toxin,  action  of.  421  ;  toxin,  detection  of  in  meat, 
420 ;  toxin,  preparation  and  resistance  of,  421 ; 
see  Botulism. 
Bacillus  chancri  mollis    (bacillus  of  Ducrey  ;  bacillus  of 

soft  chancre)    569 

Cultivation,  morphology,  phagocytosis  of,  suscepti- 
bility of  animals  to.  570. 

Bacillus    ot    chicken    cholera 166 

Bacillus    coli    communis 463,  469 

Agglutination  of,  206,  208,  225,  469 ;  antagonism 
for  putrefactive  bacteria.  464,  465 ;  antiserums, 
properties  of,  468  ;  beneficial  functions  of.  464  :  in 
cystitis,  468  ;  in  enteritis,  142,  466.  468  ;  group 
agglutination.  225 ;  group  of.  463 :  in  meningitis, 
556  ;  morphology  and  staining  of,  463  ;  occurrences 
in  intestines.  463.  464;  occurrence  in  Nature,  463; 
in  pneumonia,  502  ;  resistance  of,  46:5,  464  ;  serums, 


INDEX.  7G5 

PAGE 

effect  of,  on,  464  ;  cymbiosis  with  Avieba  coli,  C87  ; 
toxin  of,  4()8  ;  typical  strains  of.  4(54  ;  virulence  of, 
465,  466,   467. 

Bacillus    diphtherice    25,    398,  399 

Agglutination  of,  407  ;  antitoxin  for,  203,  404,  406 ; 
morphology,  staining,  cultivation,  resistance,  via- 
bility of,  390  ;  occurrence  of,  in  the  body,  400.  401  ; 
pneumonia,  in,  502  ;  toxic  action  of,  31,  32  ;  toxins 
of,  177,  178,  400.  401.  406 ;  toxin,  attenuation  of, 
142,  363;   tuberculosis,  in.  591;  see  Diphtheria. 

Bacillus  of  Ducrey.     See  Bacillus  chancri  mollis. 

Bacillus  dusenteriW'    25.  453,  455 

Agglutination  of,  206,  208,  453,  454  ;  antiserums  for, 
properties  of,  458  ;  cultivation  and  morphology  of, 
453.  454  ;  dissemination  of,  457  ;  endotoxin  of,  456  ; 
etiologic  role  of.  454  ;  "Flexner"  type  of.  453 ; 
pseudodysentery  bacilli,  453  ;  toxicity  of,  456  ;  toxin, 
autolytic,  of,  456 ;  types  of.  453 ;  see  Dysentery, 
acute  epidemic. 

Bacillus  edemw  maligna: 13,  29 

Bacillus    enteritidis    459-463 

Agglutinins  and  agglutination  of,  208.  463  ;  Bacillus 
paratyphosns,  resemblance  to,  450 ;  discovery  of, 
460 ;  fermenting  powers  of,  460  ;  group  agglutina- 
tion, 225  ;  group  of,  460  ;  meat  poisoning  by,  459 
463 ;  morphology  and  staining  of,  460  ;  occurrence 
of,  in  meat  of  horses  and  cattle,  460.  461,  462 ; 
poisoning  by  oysters  and  fish,  in.  462 ;  resistance 
of,  462  ;  toxin.  4Q0,  461 ;  toxin,  occurrence  in  meat, 
462  ;  toxin,  resistance  of,  462. 

Bacillus   of   Friedlander ;    see   Bacillus   pneumonia'. 

Bacilli   from  butter,  grass  and  milk 614 

Bacillus  ictcroidcs,  in  yellow  fever 712,  713 

Bacillus    influenza     25,   564 

Agglutination  of.  569 ;  animals,  virulence  for.  565 ; 
antiserum,  properties  of,  569  ;  in  conjunctivitis.  566  ; 
cultivation  of.  564  ;  discovery  of.  564  ;  excretion  of, 
565  ;  hemophilic  properties  of,  564  ;  immunization 
with.  569  ;  in  meningitis.  556-566  :  morphology  and 
staining  of,  564 ;  occurrence  of,  in  the  body.  566 ; 
otitis  media,  in.  566 ;  peritonitis,  in.  566 :  resist- 
ance of,  565 ;  symbiosis  of,  564 ;  toxin  of,  565 ; 
tuberculosis,   in,   591 ;   see   Influenza. 

Bacillus   lactis  acrogcncs. 

Antagonistic  action  on  putrefactive  bacteria.  465 ; 
occurrence  in  intestines,  571. 

Bacillus    lepra     25.  616 

Antiserums  for,  623 ;  discovery  of,  616  ;■  endotoxin, 
question  of,  621  ;  excretion  and  occurrence  in 
nature  of.  619 ;  morphology  of.  616 ;  occurrence 
in  the  body,  620 ;  phagocytosis  of,  620,  622 ;  see 
Leprosy. 

Bacillus    of    Lustgarten 613 

Bacillus    mallei     25.  625 

Agglutination  of.  627,  cultivation,  morphology  and 
resistance  of.  624 ;  mallein.  varieties  and  prepara- 
tion of,  625  ;  meningitis,  in.  556 ;  phagocytosis  of, 
627. 

Bacillus   melitensis    500 

Agglutination  of,  499 ;  animals,  susceptibility  of,  to, 
500 ;  morphology  of,  499 ;  opsonins,  influence  of 
in  phagocytosis  of,  499  ;  serums,  effect  of,  on,  499  ; 
see  Malta  fever. 


766  INDEX. 

I'AGE 

Bacillus    mucosiis    iaiif<iil<ititN 571 

Bacillus  of  ozena 572 

Bacillus    paratyphosus    449 

Agglutination  of.  449,  452  ;  antiserums  for,  properties 
of,  452  ;  blood  cultures,  453  ;  endotoxin,  452  ;  excre- 
tion of,  451  ;  meat  poisoning  by,  450  ;  occurrence  in 
the  body,  451  :  "paracolon"  bacilli,  relation  to, 
450 ;  resistance  of,  451  ;  toxicity,  452 ;  types  of, 
450  ;  see  I'aratvplioid  fever. 

Bacillus  pestis 25,  481-484 

Agglutination   of,   208,   491  ;   cultivation   of.   481,   482  ; 
endotoxin,  resistance  of,  484  ;  involution  forms.  482  ; 
meningitis,   in,   556 ;   morphology,   481  ;   phagocytosis 
of,    490;    pleomorphism,    481;    pneumonia,    in,    502; 
resistance  and  viability,  482,  483  ;  staining  of,  481  ; 
toxicity    of    cell    bodies.    484  ;    toxin    of    TiUStig   and 
Galeotti,  484  ;  toxin,  soluble,  question  of,  483  ;  viru- 
lence, 484,  485  ;  see  Plague. 
Bacillus  pneumoniw   (bacillus  of  Friedlander)  .  .502,  571,  572 
Agglutination  of.  208,  572  ;  antagonism  for  B.  anthra- 
cis,    494;    antiserum,    572;    influenza,    5G7  ;    lesions 
caused  by,  572  ;  meningitis,  in.  550  ;   pneumonia,   in, 
502.  510.  572  ;  tuberculosis,  in,  565. 
liacillus  prodigiosus. 

Antagonism  for  B.  antluacis.  494  ;  Coley's  mixture,  in, 
529  ;  symbiotic  action  of,  315. 

Bacillus  psittacosis,  agglutination   of 208,   225 

Bacillus  pseudotuberculosis,  varieties  of 615 

Bacillus  pyocyaucus    422-425 

Agglutination  of,  206,  208 ;  agglutinins  for.  425 ; 
agonal  invasion  by.  422  ;  antagonism  for  B.  anthra- 
cis,  494  ;  antitoxin.  424 ;  bactericidal  serum  for, 
494  ;  ferments  of,  423  ;  endocarditis,  in.  422  ;  endo- 
toxin of,  423 ;  enteritis,  in,  143 ;  infections,  symp- 
toms of,  424  ;  meningitis,  in,  423  ;  pigments  of,  424  ; 
pyocyanase,  424  ;  pyocyanolysin,  424  ;  pyocyanin, 
424  ;  secondary  infections  by,  423  ;  septicemia  in, 
423  ;  toxin,  soluble,  177.  424,  425  ;  tuberculosis  in, 
565. 

Bacillus  of  rhinoscleroma 572 

Bacillus  of  symptomatic  anthrax 315 

Bacillus  tetani 408-419 

Agglutination,  419  ;  anaerobic  property  of,  410 ;  ani- 
mals, susceptibility  of,  to  toxin.  15(5;  avirulent 
strains,  412  ;  discovery  of,  408  ;  morphology,  stain- 
ing, cultivation,  408,  409  ;  occurrence  in  intestines, 
409  ;  occurrence  in  nature,  409  ;  parasitic  power  of, 
410;  pathogenic  properties  of,  413:  resistance  of 
spores  of,  410  ;  toxins  of,  177,  178.  412  ;  toxin,  ab- 
sorption of,  by  leucocytes,  321  ;  toxin,  fixation  of, 
by  tissues.  1.56.  157,  348,  349.  366,  411  :  toxin, 
attenuation  of,  363  ;  toxin,  action  of  gastric  juice 
on,  142  ;  toxin,  neutralization  of.  by  antitoxin.  368  : 
action  of  pancreatic  juice  on,  143  ;  virulence,  315  : 
see  Tetanus. 

Bacillus  tuberculosis 25,   573 

Agglutination.  608,  610  ;  agglutination,  relation  of  to 
immunity,  211;  animals,  susceptibility  of  to,  593; 
antiserums,  properties  of.  608  ;  attenuation  of,  576  ; 
avian,  612  ;  bacteria  resembling,  613  ;  bovine,  differ- 
entiation of  from  human,  583 ;  constituents,  577 ; 
cultivation,  575  ;  discovery  of,  573  ;  effect  on  tissues. 
144,    146,    588-591;    excretion     of,    581.    582,    586; 


INDEX.  707 

PAGE 

fever  produfinj;  substance  of,  577  ;  of  flsb,  013  ; 
gastric  juice,  resistance  to,  141,  570;  immunization 
with,  577,  598,  591)  ;  inflammation  of  lunf^s,  in, 
502  ;  lesions  produced  by,  577  ;  morpbolofiy  of,  574  ; 
occurrence  in  nature.  581  ;  pathogenic  properties  of, 
577  ;  phagocytosis  of,  588,  589 ;  proteins  in,  577  ; 
resistance  of,  570  ;  staining  properties  of,  575,  577  ; 
streptococcus,  influence  of,  on  cultures,  522 ;  "tox- 
albumin"'  of,  578  ;  toxic  substances,  effects  of.  577  ; 
toxins,  008,  010  ;  virulence  of,  577,  594  ;  see  Tuber- 
culosis. 

IJmillus  tijijho.siis    .' 25,   433 

Agglutination  of,  200,  207,  230,  448,  449;  antitoxin, 
(juestiou  of.  435 ;  autolysis  of.  435  ;  blood  cultures 
of,  437.  449  ;  discovery  of.  433  ;  dissemination  of. 
434  ;  endotoxin.  435  ;  excretion  of.  438  ;  extracts  of, 
447  ;  gastric  juice,  action  of,  on,  141  ;  immunization 
with.  445,  447  ;  leucocj-tes,  relation  of,  to,  442  ; 
meningitis,  in.  550  ;  morphology  of,  433  ;  occurrence 
in  body,  24,  434.  439  ;  occurrence  in  nature,  434  ; 
phagocytosis  of.  439  ;  pneumonia,  in,  502  :  resistance 
of.  434:  symbiosis  with  Aiiicba  coli,  087;  toxin  of 
Chantemesse.  447  ;  vaccines,  444,  447  ;  see  Typhoid 
fever. 

BacillKs  zcrosis 407 

liucterium  coli  conDnunc ;  see  BaciUiis  coli  communis. 

Bactericidal  serum,  substance,  etc.  ;  see  Bacteriolysins. 

Bacteriolysins    245 

Absorption  of,  by  bacteria.  251  ;  composition  of,  249  ; 
curative  value  of,  371,  375  ;  endotoxins,  action  on, 
252,  372  ;  group  reaction  with,  250  ;  immunity,  rela- 
tion of,  to.  250 ;  inactivation  and  reactivation  of. 
248.  249  ;  nature  and  selective  action  of,  240  ;  origin 
of,  from  body  cells,  147,  253  ;  properties,  general, 
245  ;  prophylactic  value  of.  371  :  specificity  of,  250  ; 
standardization  of,  253  ;  technic  of  testing,  254  ; 
therapeutic  use  of,  370  ;  see  Amboceptors  and  Com- 
plements. 

Bacteriolysis    and    bacteriolysin 245 

Bacteriolysis. 

Group  reaction.  268  ;  mechanism  of,  260  ;  Pfeiffer's 
phenomenon,  240  ;  similarity  to  hemolj'sis,  250  ;  see 
Bacteriolysins. 

Bacteriolytic  enzymes,  relation  to  immunity 172 

Bacteriotropic  substances 371,   548 

Balantidlum  coli,  .morphology,   occurrence   and   pathogen- 
icity    ". 091,   692 

Balantidium  niinutum   692 

Benzol  ring  ;  use  of,  as  an  analogy  In  Ehrlich's  theory. 
340. 

Bile. 

Bactericidal  and  antitoxic  properties  of,  142;  immune 
agglutinins  in,  209. 

Biologic  test.  283  ;  biologic  test  for  species  ;  see  Precipitins. 

"Black  Death"  :  see  Plague. 

"Blackwater  fever"  in  malaria 003 

Blastomycetic  dermatitis  ;  see  Oidiomycosis. 

Blastomycosis  ;  see  Oidiomvcosis. 

Blue  pus : 422 

Bodo  urinarius    694 

Botulism 419-422 

Absorption  of  toxin.  421  ;  antitoxin.  203.  422  :  im- 
munity.   422  ;     infected    meats,    420 ;     phagocytosis. 


7G8  INDEX. 

PAGE 

422 ;  prophylaxis,  422 ;  susceptibility,  421  ;  symp- 
toms. 419 :  tissues  affected  by  toxin,  421  ;  see 
Bacillus  botuUnus. 

Bovine  pest 26 

Bronchitis. 

In  epidemic  cerebrospinal  meningitis,  559 ;  meningo- 
coccus in.  559  ;  Micrococcus  catarrhalis  in,  551,  559  ; 
staphylococcus  in,  544  ;  streptococcus  in,  520. 

Capsulated  bacilli 571,  572 

Carbuncle,  staphylococcus  in 543,  544 

Carcinoma,  hereditary  susceptibility  to 130 

Cell  receptors  ;  see  Receptors. 

Cercomonas    intestinalis ,    morphology    and    pathogenicity 

of   692,  693 

Chancroid  ;  see  soft  chancre. 

Chemicals  in  relation  to  antibody  formation 342 

Chemotaxis    146,  307,  315 

Chicken  cholera,  attenuation  of  microl)e  of 363 

Chicken-pox   (varicella )    743,  744 

Chicken  typhus  or  chicken-pest 26 

Cholera 25,  469-480 

Accidental,  in  man.  478  ;  agglutination  reaction,  480  ; 
animals,  susceptibility  of,  to.  474  ;  antibodies,  origin 
of,  320,  479  ;  antitoxic  serum,  480 ;  bactericidal 
power  of  body  fluids,  478  ;  "cholera-carriers,"  469, 
478 ;  diagnosis,  bacteriologic.  480 ;  epidemiology, 
473,  474,  476,  477  ;  experimental,  in  man,  478  ;  gas- 
tric juice,  protective  action  of,  478  ;  geographic  dis- 
tribution of,  473  ;  immunity  and  susceptibility  to, 
161,  169,  320,  478,  479  ;  infection  atrium,  472 ; 
lesions,  intestinal,  475  ;  effect  of  leu>^otoxic  serum  on 
infections,  298  ;  mechanism  of  intoxication,  475  ; 
mixed  immunization  in,  378,  480 ;  phagocytosis, 
378,  319.  478,  479 ;  phagolysis,  318 ;  prophylaxis, 
362,  472,  476;  serum  properties  in,  211;  sero- 
therapy, 374,  480 ;  sources  of  infection  and  trans- 
mission. 472-474 ;  vaccines  and  vaccination,  166, 
477.  478  ;  see  Vibrio  cholerw. 

Cholesterin,  neutralizing  action  on  tetanolysin 204 

Chromophages 309 

Cladothrix,  infections   with 634 

Clavelee    (sheep-pox)     26,  743 

Co-agglutinins   225 

Cobra-lecithid    275 

Cobra  venom  ;  seen  Venoms. 

Coccidia,    life    cycle,    morphology,    spore    formation    and 
pathogenecity,  694,  695. 

Coccidiosis    G94,  695 

Coccidium   bipeminum    695 

Coccidium  cunicuU  s.  oviforme 695 

Cocobacteria  septica    (Billroth) 515 

Coley's    mixture     529 

Colle's  law  ;  see  Syphilis. 

Colloids   242-244 

Complement. 

Absorption  of,  259,  373  ;  analysis  of,  277  ;  decrease  of 
during-  disease.  374 ;  diversion  of.  272,  373.  374  ; 
inhibition  of.  280  ;  isolation  of,  255  ;  lecithin  as  a, 
274;  multiplicity  of.  268,  354:  origin  of,  253,  310; 
neutralization  of.  by  salts,  204,  270 ;  receptors  of 
second  order.  351  ;  resistance  to  heat,  249 ;  solu- 
tions  of   258 ;    sources   of.    for   bactericidal   scrums, 


INDEX  769 

PAQB 

372,  373  ;  specificity  of,  266 ;  structure  of,  263  ;  uni- 
city,  theory  of,  354  ;  see  Cytase. 

Complement  deviation    279-291 

Antibody  of,   281  ;   as   biologic  test,   283  ;   in   syphilis, 
284  ;  in  other  diseases,  284  ;  nature  of,  281  ;  relation 
of  amboceptor  to,  283  ;  uses  of,  283. 
Complementophilous  haptophore  ;  see  Haptophore. 

Complementoid 264,  353 

Vomplementoid-Verstopfung    264 

Conjunctivitis. 

B.  inflenzce,  in,  566,  567  ;  diphtheritic,  400  ;  meningo- 
coccus in,  559  ;  pneumococcus  in,  514,  515  ;  staphy- 
lococcus  in,   544. 

Connective  tissue,  rOle  of,  in  inflammation 144,   148 

Contact  infection   19 

Contagion  and  contagiousness 18 

Contagious  disease,  definition 18 

Copula  of  Miiller.  synonyms  for 263 

Cow  pox   738,   743 

Crotin    218,  427 

Cryptogenetic  infections   34 

Crystalloids,  properties  of 243 

Culix  fatigans 728 

Culex  pipiens,  in  transmission  of  malaria  of  birds 670 

Curative   injections    364 

Cyclaster   scarlatinalis    744 

See  Scarlet  fever. 

Cystomonas  tirinarius    694 

Cytase    308,   311,  312 

See  Complement. 

Cytophagic  index   332 

Cytoryctes  varioJce  s.  vaccincc 731 

Conjugation.  732,  733 ;  cytoplasmic  stages,  732 ;  life 
history  of,  732-734  ;  nuclear  stages,  733  ;  small-pox, 
in,  731  ;  vaccinia,  in,  733. 

Cytotoxins   (Cytolysins)    160,  173,  292,  305 

Activity,  determination  of,  294  ;  amboceptors  in,  295  ; 
antileukotoxin.  299 ;  antinephrotoxin,  300 ;  anti- 
spermotoxin,  296 ;  autocytotoxins.  293,  294 ;  auto- 
nephrotoxin,  299 ;  autospermotoxin.  296 ;  ciliated 
epithelium,  cytotoxin  for,  294  ;  complements  in,  295  ; 
for  malignant  tumors,  297  ;  hepatotoxins,  301  ;  in- 
fections, effect  of  leukotoxins  on,  298 ;  leukotoxin, 
297 ;  nephrotoxin.  299 ;  neurotoxins,  301 ;  origin, 
310  ;  of  venoms,  429  ;  pancreotoxin,  304  ;  specificity, 
lack  of,  303  ;  spermotoxin,  295  ;  structure  of,  295 ; 
syncytiotoxin,  301  ;  technic  of  production,  294  ;  thy- 
rotoxin,  303  ;  utility,  theoretical,  292,  298. 
Cytolysins  ;  see  Cytotoxins. 

Dacryocystitis,  pneumococcus  in 514 

Daphnia.  phagocytosis  of 313 

Dengue  fever   728,  729 

Characteristics  of,  734 ;  contagiousness  of,  728,  729 ; 
Culex  fatigans  in  transmission  of,  728 ;  etiology, 
728 ;  occurrence,  728 ;  "plasmeba"  in,  728 ;  recur- 
rences and  relapses,  729 ;  susceptibility  to,  729 ; 
transmission.  728. 

Desmon    . 263 

Deuterotoxin    196,  353 

Diphtheria 25,   28,  398-40S 

Agglutination  reaction,  407 :  bacilli,  localization  of, 
401 :  conjunctivitis,  diphtheritic.  400 ;  forms  of, 
400 ;    immunity    and    susceptibility,    161,    172.    402, 


770  INDEX 

I'AGE 

403 ;  infection  atria.  400 ;  latent,  400 ;  leucocytes 
in,  403 ;  mixed  infections  in,  31.  316.  401.  524 ; 
paralysis,  influence  of  antitoxin  on,  406 ;  predis- 
posing causes,  403  ;  pneumonia  in,  510  ;  prophylaxis, 
404 ;  pseudodiphtheria  bacilli  in.  407 ;  recurrences, 
161,  404 ;  septic.  402 :  serotherapy,  369.  404 ; 
sources  of  infection,  399,  400 :  tissues  injured  by 
toxin,  401 ;  transmission,  400 ;  see  Bacillus  diph- 
thericB. 
Diplococcvs  intracellularis  meningitidis;  see  Micrococcus 
meningitidis. 

Diplococcus    pneumonicB     501,  515 

Agglutination  of.  504  ;  alveolar  abscess,  in.  514  ;  ani- 
mals, susceptibility  of.  504 ;  conjunctivitis,  514, 
515 ;  dacryocystitis.  514 :  discovery  of.  502 ;  endo- 
toxins. 504 ;  enteritis.  514 :  group  agglutination, 
514 ;  immunization  with.  510.  511,  512  ;  influenza, 
in,  567 ;  meningitis.  514,  515.  556 :  morphology, 
staining,  and  cultivation,  502.  503 ;  neurotoxic 
strains  of,  504 :  occurrence  in  blood.  509 ;  occur- 
rence, normal.  505  ;  otitis  media,  in,  514,  515  ;  peri- 
tonitis, in,  514.  515 ;  phagocytosis  of,  505,  511 ; 
pneumonia,  in,  502.  515  ;  pneumotoxin,  504  ;  pulmo- 
nary hemorrhage,  in,  510 ;  resemblance  to  strepto- 
coccus, 503  :  resistance.  503  ;  rhinitis,  in,  514  ;  sep- 
ticemia, 514  ;  serpent  \ilcer.  514,  515  ;  tuberculosis, 
in,  593  ;  virulence,  505  ;  virulence,  increase  of,  508  ; 
see  Pneumonia. 

Diplococcus    (streptococcus)    in    rheumatic   fever 525 

Dourine  ;  see  Trypanosomiasis  in  animals. 

Droplet    infection 400 

In  diphtheria.  400 ;  in  influenza,  567 ;  in  tuberculo- 
sis. 582. 

Dust   infection    400 

In  diphtheria.  400  ;  in  influenza.  567  ;  in  tuberculosis, 
581,   582  ;  in   typhoid  fever,   436. 

Dysentery,    acute    epidemic     23,   25,  453-459 

Agglutination  reaction,  459 ;  antiserums,  properties 
of,  458';  bacilli,  dissemination  of,  by  stools.  457 ; 
bacilli,  distribution  of.  in  the  body.  455 ;  chronic. 
453,  457  :  immunity  and  susceptibility.  169.  457. 
458  ;  incubation  period,  453  ;  institutions,  occurrence 
in.  457 ;  intestinal  lesions  in.  455 ;  occurrence  of, 
453  ;  predisposing  causes  of,  457  ;  prophylaxis,  457  ; 
serotherapy,  458  ;  summer  diarrheas  of  infants,  454  ; 
transmission,  457 ;  vaccination,  458 ;  see  Bacillus 
dysenterifp. 

East    Coast    fever 76 

Eclampsia,    relation   of   syncytiotoxin    to 301 

Eczema,    relation   of  staphylococcus   to 543,  544 

Eel   serum,  antitoxin  for 203 

Ehrlich's    parital    saturation    method 193,  353 

Ehrlich's   "side-chain"   theory.      See   "Side-chain"   theory 

of  Ehrlich. 
Endocarditis. 

Colon  bacillus  in.  407  ;  gonorrheal,  553 ;  pneumococ- 
cus  in,  509,  514 ;  staphylococcus  in,  525,  544 ; 
streptococcus   in,  520,  524. 

Encephalitis,  In  epidcniic  cerebrospinal    meningitis 559 

Endocomplement    274,  430 

Kndotheliotoxin,    of    venom 428 


INDEX.  771 

Endotoxins     495 

Anthrax  bacillus,  495  ;  Bacillus  pyocyaneus,  423,  424  ; 
bacteria  containing,  370,  375  ;  cholera  vibrio,  475  ; 
diseases  associated  with,  433 ;  dysentery  bacillus, 
456 ;  failure  of  bactericidal  serums  to  neutralize, 
371  ;  glanders  bacillus,  G24 ;  of  gonococcus,  552 ; 
leprosy  bacillus,  621  ;  liberation  of,  by  bacteriolytic 
serums,  252,  372  ;  meningococcus,  558  ;  paratyphoid 
bacillus,  452  ;  plague  bacillus,  484  ;  staphylococcus, 
425,  540  ;  streptococcus,  425,  5I8  ;  tubercle  bacillus, 
577  ;  typhoid  bacillus,  435, 
Enteritis. 

Ameba  coll  in ;  see  Amebic  dysentery ;  Balantilium 
coli  in,  691  ;  Cercomanas  intestinalis  in,  692  ;  colon 
bacillus  in,  468 ;  pneumococcus  in,  514 ;  staphylo- 
coccus in,  544 ;  streptococcus  in,  520,  521,  523 ; 
Trichomonas  intestinalis  in,  693. 

Enzymes,    bacteriolytic,    relation    to    immunity 172 

Enzymes,    intracellular    306 

Epilepsy,    cytotoxin    in 304 

Epithelioma    contagiosum   of   fowls 26 

Epitoxoids     194 

Erysipelas    521 

Effect  on  tumors,  529  ;  experimental  production  of.  by 
streptococcus,  521;  in  course  cf  tuberculosis,  522; 
recurrence  of.  161  ;  staphylococcus  in,  521  ;  strep- 
tococci  in,    516,   520. 

Etiology,    infectious     22 

Etiology,     unknown     26,  697 

Excretions,    infectivity    of 37 

Exhaustion,    toxin    of 304 

Farcin  du   bceitf    634 

Farcy,    see   Glanders 25 

Fermentation,    early   studies   on 4 

Fibrin,   mechanical   value  of  in  inflammation 148 

Fixator,   synonyms   for 263 

See   Amboceptors. 

Filiaria  perstans    674 

Fish,  B.  enteritidis  in,  poisonous 462 

Fish  poisons,   antitoxins  for 203 

Fleas,  in  the  transmission  of  plague 486,  487 

Flies,   as  carriers  of  typhoid  fever 436 

Fly    transmission     65 

Fomites    715 

Food-substances. 

Fixation  of.  by  amboceptors.  352 ;  manner  of  union 
with  cells.  341  ;  non-formation  of  antibodies  for,  343. 

Foot-and-mouth    disease     26,     27 

Fowls,   epithelioma  contagiosum  of 26 

Fusiform  bacilli ;  see  Noma. 

"Gambian   Fever ;"    see   Trypanosomatic   Fever. 

Gastric  juice. 

Protective  role   of,    141,  478,   494. 

Gelatinase    538 

German  measles    (Rotheln) 750 

Glanders    (Farcy)     25,  138,  623-629 

Animals,  susceptibility  of,  623  ;  bacilli,  distribution  of 
in  the  body,  625  ;  connective  tissue  development  in, 
626 ;  diagnosis,  bacteriologic,  628 ;  healing  proc- 
esses in,  627  ;  immunity.  627  :  infection  atria.  625, 
626  ;  mallein  in  diagnosis  of,  628  ;  organs  involved, 
627 ;  phagocytosis,  627 ;  serotherapy,  628 ;  tissue 
reactions,   626 ;   see  Bacillus  mallei. 


772  I^'DEX. 

I'AGE 

Glossitia  palpalis  in  transmission  of  sleeping  sickness...   675 
Gonococcus ;    see  Micrococcus   gonorrhew. 

Gonorrhea     25,   161,  551-556 

Acute  and  chronic,  554,  555 ;  complications  of,  553, 
554  ;  immunity,  161,  554.  555  ;  ophthalmia  in,  553  ; 
phagocytosis,  552,  557  ;  reinfection,  554,  555  ;  super- 
infection, 555  ;  susceptibility  of  different  tissues  to, 
553 ;  urethral  changes,  554 ;  see  Micrococcus  gon- 
orrhew. 

Gonotoxin     553 

Grass     Bacilli     614 

Gregarina  lindemanni;  see   Sarcosporidia. 

Group  agglutination    224.  227,  449,  452,  463,  512,  536 

Gruber-Widal   reaction  ;   see  Agglutination. 

Hairs,  phagocytosis  of  pigment  by  chromaphages 309 

Halteridium. 

Impregnation  of  parasites,  654  ;  in  malaria  of  birds, 
669. 

Haptophores 192,  341,  343,  351 

Haptophorous  groups  ;  see  Haptophores. 

Hauptagglutinins    225 

Hay  fever 425-427 

Antitoxin  (pollantin),  204,  426;  pollen  as  cause  of, 
425  ;  toxin  of,  425. 

Hanging-drop  preparation 212 

Hemagglutinins. 

Of  plants,  218  ;  of  serums,  218  ;  of  venom,  428. 

Hemoglobinuric   fever,    in   malaria 633 

Hemolysins. 

Animal,  428,  432  ;  bacterial,  346  ;  cobra  lecithid,  275, 
430  ;  colloids  as,  276  ;  experimental  value  of,  256  ; 
from  organ  extracts,  310  ;  immune,  in  serums,  173, 
256  ;  intraleucocvtic,  310  ;  normal,  in  serums,  160  ; 
pyocyanolysin,  424  ;  serum  hemolysins,  structure  of, 
256 ;  staphylococcus,  see  Staphylolysin  ;  streptococ- 
cus, see  Streptocolysin  ;  tetanolysin,  413  ;  venom  of, 
428.  L 

Hemolysis  ;   see  Hemolysins. 
Hemolytic  experiments. 

Technic  of,  256  ;  value  of,  in  study  of  immunity,  256. 

Hemorrhagic  septicemia  group  of  bacteria 482 

Hemorrhagin    273,   428 

Hemotoxins    178 

Hepatotoxins 301 

Hereditary  infection 61 

Heterologous  serum   208 

Homologous  serum 208 

"Horror  autotoxicus"' 305 

Horsepox    743 

Hydrophobia   25,  697-710 

Animals,  in,  700,  701  ;  diagnosis,  in  dogs,  702.  703  ; 
extension  through  nerves,  704  ;  fixed  virus  of,  700  ; 
immunity,  character  of,  710 ;  immunization,  mixed, 
710  ;  incubation  period,  702,  704.  705  ;  micro-organ- 
isms found  in,  697 ;  Negri  bodies,  697,  698 ;  Pas- 
teur treatment,  705,  710  ;  prophylaxis  of.  704,  710  ; 
specific  lesions,  703 ;  street  virus  of,  700 ;  trans- 
mission of,  701  ;  toxin,  question  of.  698 ;  vaccina- 
tion. 6,  7,  707 ;  vaccine,  preparation  of,  705,  706 ; 
virulence  for  man,  700,  704,  707  ;  virulence,  in- 
crease and  decrease  of,  by  passage,  700 ;  virus, 
attenuation  of.  166,  363.  698,  706-710 ;  virus  de 
rue,-  700 ;     virus,     distribution     and    excretion     of, 


INDEX.  773 

PAGE 

700 ;    virus,    filterability    of,    27,    698 ;    virus    fixe, 
700,   705 ;   virus,    resistance   of,    699. 

Ichthyosismus     420 

Ichthyotoxin     432 

Immunity. 

Absolute,  135 ;  acquired,  129,  161-175 ;  active,  134, 
161.  168 ;  antibacterial,  132,  149,  154,  355 ;  anti- 
toxic, 132,  154.  155,  354 ;  definition  of,  128 ;  in 
families,  130 ;  leucocytes,  relation  to ;  see  Phago- 
cytosis ;  natural,  129,  137-160 ;  early  theories  of, 
1  ;  passive,  134,  169  ;  relative,  134  ;  theories  of,  7, 
12 ;  types  of,  135 ;  see  Antitoxins,  Bacteriolysins, 
Phagocytosis  and  the  individual  diseases. 
Immunization. 

Active,  a  curative  measure,  364  ;  active,  for  prophyl- 
axis,   376 ;    classification    of    methods.    362 ;    choice 
of  animals  for,   373 ;   mixed,   364,   378 ;   passive,   as 
curative    measure,    364  ;    passive,    in    prophylaxsis, 
364  ;  with  tissue  cells,  294  ;  with  toxins,  10. 
Impetigo  contagiosa. 
Staphylococcus    in,    520 ;    streptococcus    in,    520. 

Incubation     period     354 

Infection 

"Air  borne,"  19 ;  atrium  of,  19,  137,  141 ;  carriers, 
39 ;  contact  by.  19 ;  mixed,  26,  30,  31,  227 ;  see 
individual  diseases ;  "water  borne,"  19 ;  infectious 
agents,  classification  of,  21. 

Infectiousness    and    contagiousness 18 

Infectivity     88 

Infestation     14 

Inflammation. 

Antagonism  of.  to  infections,  148 ;  chemotaxis,  146 ; 
connective  tissue,  inflammatory  role  of,  143,  148 ; 
fibrin,  influence  of,  148 ;  injurious  effects  of,  143, 
144  ;  leucocytes  in,  145,  147  ;  nature  of,  143  ;  organi- 
zation in,  147 ;  phagocytosis  in,  145-147 ;  plasma, 
influence  of,  147  ;  relation  of,  to  virulence  of  bac- 
teria, 144,  145 ;  role  of,  in  immunity  and  resist- 
ance,  143 ;    variations    in   intensity,    144-146. 

Influenza     25,  563-569 

Conjunctivitis  in,  567 ;  chronic,  567 ;  contagiousness 
of.  563 ;  epidemics  of,  563 ;  immunity,  568 ;  infec- 
tion atrium,  567 ;  intestinal,  566 ;  intoxication, 
566  ;  meningitis  in,  566,  567  ;  mixed  and  secondary 
infections  in,  567  ;  otitis  media  in,  566,  567  ;  peri- 
tonitis in,  566,  567  ;  phagocytosis  in,  566  ;  pneumonia 
during,  510,  566 ;  prophylaxis,  568 ;  recurrence  of, 
161,  568  ;  susceptibility,  568  ;  transmission  of,  567  ; 
tuberculosis  during,  567  ;  see  Bacillus  influenzw. 
Jnsects. 

In  transmission,   67  ;  incubation  in,  81. 

"Intestinal    group"    of   bacteria 434 

Intoxication     96 

Iso-agglutinins    218 

Isoprecipitins    236 

Kala-Azar    696 

Lactoserum     235,  240 

Lamhlia   intestinalis    694 

Leischman   Donovan   Bodies :    See   Kala-Azar. 

"Leistungskern"     209,  339 

Lecithin   as  endocomplement 274 

"Leprolin"     621 


774  INDEX. 

PAGE 

Leprosy    25,  615-623 

Animals,  insusceptibility  of,  to.  618 ;  contagiousness 
of,  616 ;  distribution  of  bacilli  in  the  body.  620 ; 
extension  and  occurrence  of,  615  ;  fish,  relation  of 
to,  619 ;  infection  atria,  619 ;  intercurrent  infec- 
tions, 621  ;  phagocytosis  in,  621,  622 ;  potassium 
iodid  in  treatment  of,  621  ;  prophylaxis,  622  ;  pro- 
tective factors  in,  622  ;  serotherapy  of,  623  ;  spon- 
taneous disappearance  of.  621  ;  susceptibility  to, 
622 ;  transmission  of,  618 ;  tubercular,  621  ;  see 
Bacillus   leprcB. 

Leptothrix,   infections  by 634 

Leptothrix   huccalis    634 

Leptothrix  vaginalis    634 

Leucocidin    178.    346,    539.   547,  549 

Antitoxin  for  539  ;  influence  on  phagocytosis,  539. 
Leucocytes. 

Absorption  of  toxins  by,  321 ;  complement  in,  269 ; 
formation  of  precipitins  by,  236 ;  immunity,  rela- 
tion to,  306-323 ;  in  inflammations,  145 ;  phago- 
cytic properties  of,  145,  146,  147  ;  see  also  individ- 
ual disease  ;  see  Phagocytosis. 

Leucocytic   exudates,   bactericidal    action    of 546 

"Loop,"    standard    215 

Leucotoxic    serum     297,  298 

Leucotoxin  ;  see  Leucotoxic  Serum. 
"Lumpy  jaw  ;"   see  Actinomycosis. 

Lupus,  influence  of  streptococcus  on 529 

Lymphangitis,    streptococcus    in 520-522 

Lymphatotoxin  ;   see  Leucotoxic  Serum. 

Macrocytase     308 

Macroparasites     21 

Macrophages     146,  298,  308,  314 

Madura  foot ;  see  Mycetoma. 

Mai  de  caderas ;  see  Trypanosomiasis  in  animals. 

Malaria 654-670 

yEstivo-autumnal,  655 ;  sestivo-autumnal,  parasite  of ; 
see  Plasmodium  prcecox;  anemia  in,  690;  "black- 
water"  fever  in,  663 ;  cachexia  in,  662 ;  cerebral 
symptoms,  663 ;  epidemiology  of,  664 ;  etiology  of, 
654 ;  fever,  relation  of  to  developmental  cycles 
of  parasites,  660 ;  hemoglobinuric  fever  in,  663 ; 
immunity,  acquired,  667,  668 ;  incubation  period, 
659  ;  intestinal  symptoms,  663  ;  malanemia  in,  690  ; 
methylene  blue  in,  661 ;  mixed  infections,  662  ;  mos- 
quitoes, transmissions  by,  654  ;  neuralgia  in,  663  ;  par- 
asites, localization  of,  663  ;  prophylaxis  of,  666,  667  ; 
quartan,  655  ;  quartan,  parasites  of  ;  see  Plasmodium 
malariw,  quinin  in  prophylaxis  and  treatment  of, 
663,  666,  667 ;  quotidian,  662 ;  relation  of  clinical 
symptoms  to  developmental  cycles  of  parasites, 
663 ;  susceptibility  to.  667 ;  tertian,  655 ;  tertian, 
parasite  or ;  see  Plasmodium  xivax :  toxins.  661  : 
transmission  ;  see  Anopheles ;  see  Plasmodium  of 
malaria. 

Malaria  of  birds,  haltoridium  in;  proteosoma  in 669 

Malignant  pustule  ;  see  "Anthrax." 

Mallcin     364,  625,  628 

Malta    Fever    498-500 

Accidental  infections,  500 ;  agglutination  reaction  in, 
499 ;  difference  from  typhoid  fever,  499 ;  distribu- 
tion of  bacillus  in  body,  499,  500  ;  immunity,  500  ; 
occurrence.    498 ;    serum,    properties    of,    499 ;    sero- 


INDEX.  775 

PAQB 

therapy,  500  ;  transmission,  500  ;  see  Bacillus  meli- 
tensis. 
Measles     747-750 

Complications  and  sequelae,  749 ;  contagiousness  of, 
748  ;  Immunity  and  susceptibility,  749  ;  leprosy,  in- 
fluence on,  021  ;  leucocytes  in,  750 ;  Micrococcus 
catarrhalis  in,  550 ;  micro-organisms  in,  747 ;  pro- 
piiylaxis,  749  ;  racial  immunization,  749  ;  resistance 
of  virus,  749  ;  recurrences,  749  ;  serotherapy,  750  ; 
virus,   distribution  of,   748. 

Meat  poisoning. 

Bacillus    hotuUnus    in,    419 :    Bacillus    enteritidis    in, 
459-4G.3  ;  Bacillus  paratyphosus  in,  450  ;  relation  of 
•     ptomaines  to,  460. 

Mediterranean  fever  ;  see  Malta  fever. 

Meningitis. 

B.  pneumonifB  in,  572  ;  colon  bacillus  in,  467  ;  in  influ- 
enza, 566 ;  micro-organisms  causing,  319,  556 ; 
pneumococcus  in,  509,  514 ;  secondary,  522 ;  strep- 
tococcus  in,   520,    522,   524 ;   tuberculous,   587. 

Meningitis,   epidemic   cerebrospinal 556-56.3 

Agglutination  test,  560 ;  cerebrospinal  character  of, 
559 ;  complications,  559 ;  contagiousness  of,  559 ; 
immunity,  acquired,  560  ;  lumbar  puncture  for  diag- 
nosis, 559 ;  metastatic  infections,  559 ;  mixed  and 
secondary  infections  in,  559  ;  prophylaxis  of,  560 ; 
secondary  to  rhinitis,  558 ;  serum  properties  of, 
560 ;  susceptibility  to,  560 ;  transmission  of,  559 ; 
see  Micrococcus  meningitidis. 

Meningococcus  ;  see  Micrococcus  menimjitidis. 

Metchnikoff's   theory ;   see   Phagocytosis. 

Methylene  blue,  effect  of,  on  malarial  parasites 661 

Microbic    specificity     4 

Micrococcus    catarrhalis     550,  551 

Animals,  susceptibility  of,  to,  551  ;  bronchitis,  in,  551, 
559  ;  measles  in,  550  ;  occurrence  in  respiratory 
passages,  550  ;  occurrence  under  normal  conditions, 
551  ;  pneumonia,  in,  502,  510,  551.  560  ;  resemblance 
to  meningococcus,  560 ;  scarlet  fever  in,  550 1 
whooping-cough,  in,  550. 

Micrococcus    gonorrhece    (gonococcus) 383 

Antiserum  for,  555  ;  cultivation  of,  551  ;  discovery  of, 

551  ;  endotoxin  of,  552  ;  gonotoxin,  553  ;  immuniza- 
tion with,  555 ;  infections  with,  551,  555 ;  mor- 
phology,   551  ;    phagocytosis   of   552 ;    resistance    of, 

552  ;   toxin,   soluble,   555  ;   see   Gonorrhea. 

Micrococcus    hematodes     541 

Micrococcus  melitensis ;  see  Bacillus  melitensis. 
Micrococcus     rneninfjitidis      (Diplococcus     intracellularis 

meningitidis,    or    the    meningococcus) 25,  556-563 

Agglutination  of,  560 ;  animals,  susceptibility  of,  557 ; 
antiserum,  properties  of,  561  ;  bronchitis,  in,  559 ; 
conjunctivitis  in,  559 ;  cultivation,  557 ;  discovery, 
556 ;  endotoxin,  558 ;  excretion  of,  559  ;  immuniza- 
tion with,  560 ;  morphology,  557 ;  pneumonia,  in, 
559 ;  resemblance  to  gonococcus,  557 ;  resemblance 
to  Micrococcus  catarrhalis,  559 ;  resistance,  557 ; 
rhinitis  in,  559 ;  virulence,  558 ;  see  Meningitis, 
epidemic   cerebrospinal. 

Microcytase    308-319 

Micro-organisms. 

Acquired  resistance  of,  116  ;  early  belief  in,  2  ;  excre- 
tion of,  37;  recognition  of,  3;'sources  of,  in  earth. 


776  .         INDEX. 

PACK 

41 ;  in  water  food,  42 ;  in  insects,  44  ;  in  man,  47  ; 
in  air,  49  ;  ultramicroscopic,  21  ;  viability  of,  55. 

Microparasites    21 

Microphages    146,    308,    314,   320 

Microsporon   septicum     (Klebs)     515 

Milk  bacilli   614 

Mitagglutinin    225 

"Monadinin"    of    Klebs 525 

Mucor     641 

Mumps    (epidemic  parotitis) 755 

Mycetoma    633 

Nagana  ;   see  Trypanosomiasis  in  animals 680 

Natural  immunity ;   see   Immunity. 

"Negative  phase"   following  vaccinations 377 

Negri  bodies  ;  see  Hvdrophobia. 

Nephrotoxin    299,  300 

Neuronophages      309 

Neurotoxin    of    serums 301 

Neurotoxin  of  venom   178,  428 

Noma     758-759 

Oidia     21,  25 

Oidiomycosis     635-641 

In  animals,  640  ;  cutaneous,  635  ;  infection  atria,  638  ; 
organisms  of,  636 ;  resemblance  to  tuberculosis, 
638 ;    systemic.    635 ;    thrush,    639. 

Oidium     635 

Agglutination,    immunization    and    phagocytosis,    640. 

Oidium  albicans   639 

Oidium     coccidiodes     637 

Old  age,  Metchnikoff's  theory  of 298 

Ophthalmia. 

Cvtotoxins  in,   304  ;  gonorrheal,   553. 

Opsonins     324-338 

As  distinct  antibodies,  329 ;  immune  opsonins,  328 ; 
interaction  with  leucocytes,  332 ;  normal  opsonins, 
330 ;  opsonic  index,  325 ;  proof  of  action  of,  324  ; 
relation  to  immunity,  330  ;  relation  to  virulin,  338  ; 
specificity  of,  328. 

Opsonocytophagic    index     332 

Otitis  media. 

B.  influenzw  in.  566.  567 ;  pneumococcus  in,  514 ; 
staphylococcus  in,  544  ;  streptococcus  in.  524  ;  tuber- 
culous, 587. 

Oxytuberculin      580 

Ozena    572 

Pancreatic    .iuice,    action    on    toxins 142 

Pancreotoxin     304 

"Paracolon"'   bacilli    450 

Parasites,    pathogenic     13,  21 

Parasitism     13 

Paratyphoid     Fever     449-453 

Agglutination  reaction  in,  452  ;  blood  cultures  in,  453  ; 
characteristics  of  the  disease,  451  ;  endotoxin  of 
bacilli,  452  ;  epidemiology  of.  450  ;  as  meat  poison- 
ing, 450 :  occurrence  of  bacilli  in  the  body,  451  ; 
properties  of  serum,  452  ;  prophylaxis.  452  ;  trans- 
mission. 450,  451  ;  see  BaciUus  paratijphosus. 
Parotitis,  epidemic ;  see  Mumps. 

Passage     91 

Passive  immunity  ;  see  Immunity. 
Pasteur   treatment ;   see   Hydrophobia. 

Pathogenesis    88 

Peripneumonia  of  cattle    26,  27 


INDEX.  777 

PAGE 

Periostitis   album Inosa    545 

Periostitis,     staphylococcus     in 545 

Peritonitis. 

Colon    bacillus    in,    468 ;    by    influenza    bacillus,    566, 
567  ;  pncumococcus  in,  513,  514  ;  staphylococcus  in, 
544 ;   streptococcus   in,   520,   523 ;   tuberculous,   587. 
Pertussis  ;  see  Whooping-cough. 

Pfeiffer's    phenomenon     210,  246 

In    indentifying    the    vibrio    of    cholera,    471  ;    rOIe    of 
leucocytes  in,  318. 
Phagocytic    (Metchnikofif's)    theory  of  immunity.  ..  .306,  331 
Comparison  of,  with  the  side-chain  theory  of  Ehrlich, 
356,   357  ;   see  Phagocytosis. 

Phagocytosis   9,  146.  306-331,  354 

In  active  immunity,  168,  169,  324,  325 ;  chemotaxis 
in,  307,  315  ;  fixators,  influence  of,  320  ;  in  inflam- 
mations, 145 ;  intestinal,  143,  307 ;  intravascular, 
318 ;  leucocidin,  influence  of,  539 ;  in  nutrition. 
302  ;  in  passive  immunity,  169  ;  relation  of  to  viru- 
lence of  bacteria,  314,  317 ;  in  resorption,  308 ; 
serum,  influence  of,  317 ;  in  vitro,  153  ;  see  under 
the  individual  micro-organisms  and  diseases ;  see 
Opsonins. 

Phagolysis    311,   312,   318.  320 

Phallin   428 

Phrynolysin     431 

Phytoprecipitins    235 

Placental    transmission     60 

Plagiomonas  urinaria    694 

Plague    25,  481-492 

Agglutination  reaction,  492  :  animals,  susceptibility  of. 
484 ;  contagiousness,  487  ;  diagnosis,  bacteriologic 
488 ;  dissemination  of  bacillus  by  urine,  feces, 
sputum,  487  ;  epidemiolog-v.  487,  488  ;  foci  of.  485  : 
immunity,  161,  169,  489,  490  ;  infection  atria,  487  ; 
mixed  immunization  in,  489 ;  mixed  infection  in. 
488 ;  occurrence,  481  ;  houses,  487 ;  prophylaxis, 
488  ;  in  rats,  486  ;  serum  therapy,  490,  491  ;  trans- 
mission by  fleas,  486  ;  transmission  from  rat  to  man. 
486,  487  ;  vaccination.  166,  362,  389  ;  vaccines,  489. 
490  ;  see  Bacillus  pestis. 

Plasmin    of    Buchner 179,  363 

Plasmodia   of   malaria 25.  654 

Anopheles  mosquito  as  host  of,  24,  655 :  asexual 
cycle,  656;  development  in  anopheles,  656;  devel- 
opment in  man,  655  ;  discovery  of,  654  ;  flagella  of, 
654  ;  macrogamete,  656  ;  morozoites.  656  ;  methylene 
blue,  effect  of,  661  ;  microgamete,  656 ;  microgamo- 
tocyte.  656  ;  oocyst,  657  ;  ookinet,  657  ;  schizogony, 
656,  660  ;  sexual  cycle,  656  ;  species  of.  655  ;  sperma- 
tozoites,  654 ;  sporocyte,  656 ;  sporogony,  657 ; 
sporozoites,   657  ;  see  Malaria. 

Plasmodium    malariw    655 

Relation  to  clinical  symptoms,  659  ;  sexual  and  asex- 
ual cycles  of,  656 ;  virulence,   660. 

Plasmodium     prwcox     655 

Relation  to  clinical  symptoms,  659  ;  sexual  and  asex- 
ual cycles  of,  658  ;  virulence,  660. 

Plasmodium    vivax     655 

Asexual   cycle   of,   650 ;    relation    of   to   clinical   symp- 
toms, 659  ;  sexual  cycle  of,  656  ;  virulence,  660. 
Pneumococcus ;   see  Diplococcus  pneumoniw. 


778  INDEX. 

PAGE 

PDeumonia    501,  513 

Agglutination  reaction,  512 ;  B.  pneumonice  in,  572 ; 
bacteria  causing,  501.  502 ;  causes,  predisposing, 
508 ;  complications.  509,  510,  513 ;  contagiousness, 
507 ;  immunity  and  susceptibility.  161.  510 ;  infec- 
tion atrium  and  method  of  infection,  505  ;  Influenza 
bacillus  in,  566 ;  leucocytes,  511  ;  metastatic  infec- 
tions, 513 ;  phagocytosis,  511  ;  meningococcus  in. 
550 ;  Micrococcus  catarrhalis  in,  551.  559 ;  mixed 
infections  in,  510  ;  polyvalent  serum  for,  512  ;  pro- 
phylaxis, 510 ;  recurrences,  510 ;  Roemer's  serum, 
512  ;  serum  properties,  510  ;  serotherapy,  511,  512  ; 
staphylococcus  in,  544 ;  streptococcus  in,  520,  521, 
522 ;  vaccination,  510 ;  see  Diplococciis  pneumoniw 
and  other  bacteria  enumerated  on  page  502. 

Pneumotoxin    504 

Poliomyelitis     (epidemic)     756-758 

Dissemination.  758 ;  experimentally  produced,  757 ; 
micro-organisms   in,   757  ;   virus  distribution  of,  757. 

Pollantin    426 

Pollens. 

As  cause  of  hay  fever,  425  ;  antitoxin  for,  426. 

Polyceptors    269 

Polyvalent  serums. 

For  pneumococcus.  512  ;  for  staphylococcus,  550  ;  for 
streptococcus,   376,    533. 

"Positive    phase"    following    vaccination 377 

Post-mortem    invasion     467 

Precipitate     235,  240,  241 

Precipitation    reaction     230,  234 

Agglutination,  relation  to,  230 ;  as  clinical  reaction, 
234 ;  with  colloids  and  electrolytes.  244 ;  forensic 
use  of,  174,  241  ;  precipitation,  group  reaction. 
240,  241 ;  meats,  differentiation  of,  242 ;  physical 
chemistry  in  the  study  of,  244  ;  specific  inhibition. 
237  ;  technic,  241 ;  use  of  in  studying  reactions  of 
immunity,  350. 

Precipitins    234-244 

Antiprecipitins,  238 ;  autoprecipitins,  236 ;  bacterial, 
174,  234.  377,  479 ;  formation  of,  236 ;  isoprecipi- 
tins,  236 :  lactoserum,  235 ;  phytoprecipitins,  235 ; 
resistance  to  ferments,  heat,  etc..  237 ;  serum  pre- 
cipitins, immune.  174 ;  serum  precipitins,  normal, 
160  ;  structure  of,   237  ;  zooprecipitins,  235. 

Precipitinogens   235 

Precipitoids     238 

Pregnancy,     serum     diagnosis 302 

Preparator 263 

Proagglutinoids     223 

Prophylactic    in.iections,    classification    of    methods 362 

Protective  inoculation  ;   see  Vaccination. 

I'roteins     364 

Proteosoma  in  malaria  of  birds 669 

Prototoxin     196,  353 

I'rotoxoids    196,  353 

Protozoa,     infections    with 654,   695 

Pseudodiphtheria   bacilli    407,  591 

I'seudoinfluenza    bacilli     564 

Pseudotuberculosis  of  animals 614 

Ptomains    in     meat     460 

Pyocyanase     172,  423 

Pyocyanin    423 


INDEX.  779 

FAGK 

Pyocyanolysin     424 

Pyroplasma  boiis;  see  Texas  fever. 

Pyroplasma  Jiominis;  see  Spotted  Fever. 

Pyroplasmas,    inheritance    of 77 

Pyroplasmosis  ;   see   Spotted  fever  and  Texas  fever. 

Rabies,   See  Hyropliobia. 

Radium,    effect    on    venom 431 

Rats  in  epidemics  of  plague 486,  487 

Rattlesnake   venom. 

Antiserum  for,  431  ;   immunization  with,   363. 

Ray    fungus  ;    see    Actinomyces 486,  487 

Receptors. 

Bacterial,  267  ;  function  of,  156,  200,  201  ;  immunity, 
relation  to,  343  ;  loss  of,  as  cause  of  immunity, 
403 ;  multiplicity  of,  200,  352 ;  new  formation  of, 
343,  349,  351  ;  nutrition,  relation  to,  339 ;  of  first 
order.  203,  344.  351  ;  of  second  order,  228,  347, 
351,  353  ;  of  the  third  order,  265,  347,  351  ;  syno- 
nym for  side  chain,  341  ;  tetanophile  receptors  of 
nervous  tissue,  415 ;  types  of,  351  ;  see  different 
antibodies.      Recrudescences,   101  ;   recurrences.   101. 

Relapsing  fever    25,   642-646 

Agglutination  test,  645  ;  immunity  and  susceptibility, 
644,  645 ;  organism  of,  see  Spirocheta  obermeieri; 
phagocytosis  in,  644  ;  prophylaxis,  644  ;  serum  prop- 
erties. 645 ;  serotherapv,  645 ;  transmission  of  bv 
bedbugs.  643. 

Resistance,   natural ;   see   Immunity,   natural. 

Resorption. 

Of  foreign  cells,  309  ;  of  native  cells,  308. 

Rheumatic    fever     525-527 

Agonal  invasions  in,  525  ;  antistreptococcus  serum  in, 
535 ;  bacillus  of  Achalme  in,  525 ;  diplococcus 
(streptococcus)  in.  526 ;  experimental,  525.  526 ; 
micro-organisms  found  in  lesions,  525  ;  staphylococ- 
cus in,  525 ;  streptococcus  in,  520,  525,  526 ; 
Zymotosis   transJucens,  525. 

Rhinitis. 

Meningococcus  in,  559 ;  pneumococcus  in.  514  ;  pri- 
mary to  meningitis,  558 ;  staphylococcus  in,  544 ; 
Rhinitis  fihrinosa,  400. 

Rhinoscleroma     572 

Ricin    21,  427 

Antiricin,  174  ;  Ehrlich's  use  of  in  studying  nature  of 
antitoxic  action,  345,  346  ;   hemagglutinin  in,  218. 

Robin 427 

Rotheln,    see   German   measles. 

Saccharomycosis  liominis    635 

Salamander   poison,    antitoxin   for 203 

Saprophytes     13 

In    tetanus    411 

Sarcocystitis  Jiominis;  see  Sarcosporidia. 

Sarcosporidia. 

Morphology,  occurrence  and  proliferation,  690,  691  ; 
Sarcocystis  hominis,   691. 

Scarlatina  ;   see   Scarlet   fever. 

Scarlet   fever    (scarlatina) 744-747 

Agglutination  of  streptococci  by  serum,  536,  537  ;  con- 
tagiousness, 745 ;  Cyclaster  scarlatinalis  in,  744 ; 
Diplococcus  scarlatinw,  26 ;  leucocytes  in,  746 ; 
Micrococcus  catarrhalis,  550 ;  micro-organisms  in, 
745 ;    prophylaxis,    745 ;    protozoa    in,    25,    744 ;    re- 


780  INDEX. 

PAGE 

sistance  of  virus,  745 ;  serotherapy,  747 ;  strepto- 
coccus in,  31,  316,  520,  521,  523,  527,  744  ;  Strep- 
tococcus scarlatinw,  527 ;  immunity  and  suscepti- 
bility, 161.  746;  sero-therapy  (antistreptococcus), 
533,    534,    747  ;    transmission,    745. 

Scorpion,     toxin     and     antitoxin 203,  432 

Sensitization     259 

Serpent  ulcer. 

Pneumococcus  in,  514,  515 ;  treatment  with  anti- 
pneumococcus  serum   (Roemer),  515. 

Serum    disease    395 

Serums,  purity  of   189,   365 

Serotherapy,    principles    of 362-380 

Antitoxins,    365,    370 ;    bactericidal   serums,   370,    376 ; 
classification   of   methods,   362 ;   curative   injections, 
364,    367,    371  ;    prophylactic    injections,    362,    370. 
371  ;  see  also  under  the  different  diseases. 
Sheep-pox  ;  see  Clavelee. 

Side-chain   theory  of  Ehrlich 339-361 

Amboceptor  formation,  264  ;  agglutinin  formation,  228  ; 
antitoxin  formation, 199,  202  ;  applied  tocellnutrition, 
339 ;  as  applied  to  immunity,  343 ;  chemical  pro- 
cesses, 191,  344,  348,  351  ;  complements.  268,  354  ; 
essential  tenets  of,  344 ;  haptophores,  341  ;  "Leis- 
tungsJcern,"  339 ;  Metchnikoff's  phagocytic  theory, 
comparison  with,  356,  361  ;  precipitin  formation, 
236  ;  receptor  proliferation,  349  ;  receptors,  types  of, 
351  ;  side  chains,  339. 

Sleeping     sickness     673-678 

Anatomic  lesions  of,  676  ;  bacteria  in,  674  ;  occurrence, 
674,  675  ;  symptoms  of,  675,  676  ;  transmission  of, 
675 ;  Trypanosomatic  fever,  relation  to,  676,  677 ; 
trypanosomes  in,  674  ;  see  Trypanosomiasis. 

Small-pox    729-743 

Bacteria  in,  730,  736 ;  conversion  into  vaccinia,  729, 
730 ;  cyclic  nature  of  symptoms,  735 ;  Cytoryctes 
variolce  s.  vacciniw,  731  ;  dissemination  of  virus, 
734  :  etiology,  730  ;  fetal,  731  ;  immunity  and  sus- 
ceptibility, 164,  742  ;  incubation  period,  735  ;  infec- 
tion atrium,  734  ;  inoculation  into  calves,  729  ;  jen- 
nerization,  737;  leucocytes  in,  742;  mixed  (second- 
ary) infections,  30,  736 ;  nonfiltrability  of  virus, 
730  ;  prophylaxis,  736  ;  protozoon-like  bodies  in,  26, 
730 ;  relation  to  vaccinia,  165,  729  ;  revaccination, 
740,  741  ;  serum  properties,  742  ;  transmission,  734  ; 
vaccination,  736 ;  vaccine,  contaminations  of,  739, 
740 ;  vaccine,  durability  of.  739  ;  virulence,  varia- 
tions in,  735  ;  virus  distribution  in  the  body,  735. 

Small-pox  and  vaccinia 729,  743 

Smegma  bacilli   613 

Snake  bites 428,  431 

Soft  chancre  or  chancroid 569-571 

In  animals,  570 ;  bacillus  of.  570  ;  immunity,  571  ; 
independence,  569 ;  infectiousness  of,  569 ;  phago- 
cytosis. 570,  571. 

Specific  infections 9 

Specificity  in  transmission 86 

Spermophilus  columbianns  as  host  of  Pyroplasma  hominis  721 

Spermotoxin    295,  296 

Spider  poison,  antitoxin   for 203 

Spirocheta. 

Anserina,  653  ;  disenses  due  to,  642  ;  gallinarum,  653  ; 
pallida  ;  see  Syi)hilis  ;  pertenuis,  652  ;  Theileri,  653. 


INDEX.  781 

PAGE 

Spirocheta  obermeieri 25,  642 

Animals,  susceptibility  of,  643  ;  antiserums,  properties 
of.  644  ;  distribution  in  tbe  body,  643  ;  morphology, 
642 ;  occurrence  in  bedbugs,  643  ;  phagocytosis  of, 
644,  645  ;  see  Relapsing  fever. 

Spotted  fever 73,   720-725 

Immunity  in,  725 ;  maintenance  of,  723 ;  micro- 
organisms in,  724 ;  pyroplasma  hominis  in,  720 ; 
transmission  to  man,  722 ;  to  other  animals,  722 ; 
transmission  by  ticks,  721,  723. 

Staphylococcus  pyogenes,  or  staphylococcus 537-550 

Agglutination,  206.  549 ;  amyloid  degeneration,  542 ; 
animals,  susceptibility  of,  543 ;  antiserums,  prop- 
erties, 547 ;  bactericidal  action  of  leucocytic  exu- 
dates, 546  ;  bacteriolysin,  546.  547  ;  discovery,  516  ; 
endotoxin,   540  ;  ferments  of,  538  ;  hemolytic  action, 

538,  539 ;     immunity,    316.    546,    547 ;     leucocidin, 

539,  547,  549  :  leucocytes  in  infections,  545,  546 ; 
leucotactic  substance,  542 ;  mixed  infections,  545 ; 
morphology,  537  ;  necrotizing  substance,  542  ;  path- 
ogenic powers,  139,  501,  510.  520,  525,  543,  544, 
556 ;  opsonins  in  phagocytosis  of,  549 ;  phagocy- 
tosis, 545,  546,  548  ;  pigment  formation,  541  ;  poly- 
valent serum.  550;  resistance,  541,  542;  staphy- 
lolysin,  435,  539,  542,  547  ;  symbiosis  with  Ameha 
coli,  687  ;  symbiosis  with  B.  influenzw,  564  ;  toxicity 
of  culture  filtrates,  539,  540 ;  toxin,  soluble,  542 ; 
vaccination  against,  548  ;  varieties,  540,  541  ;  viru- 
lence,  543. 

Staphylolysin ;    see    Staphylococcus. 

Stegomyia  fasciata  and  its  relation  to  yellow  fever....    713 

Streptococci  in   scarlet  fever 26,   520,  523,  527 

Streptococcus   hrevis    516 

Streptococcus  erysipelatis   516 

Streptococcus    longus     516 

Streptococcus  mucosus  capsulatus 516 

Streptococcus    pyogenes     517-537 

Agglutination.  206.  536,  537 ;  animals,  susceptibility 
of,  518  ;  antagonism  for  B.  anthracis,  494,  528  ;  for  B. 
tuberculosis,  522  ;  antistreptococcus  serum,  properties 
of,  529,  535  ;  antistreptocolysin,  519  ;  Coley's  mixture, 
529  ;  cultivation.  517  ;  in  diphtheria.  401.  524  ;  discov- 
ery, 515  ;  endotoxin.  518  ;  erysipelas,  515.  520,  521  ; 
immunity,  316,  529,  530.  531  ;  infection  atria,  524  :  in- 
fections,"^miscellaneous,  520.  529  ;  in  influenza,  567  ; 
leucocytes  and  leucocytosis,  530,  531  ;  in  meningitis. 

520,  557;  in  milk,  523;  morphology,  515;  opsonins. 
531  ;  phagocytosis.  530,  531  ;  in  pneumonia,  501, 
510,  520,  521,  522  ;  resemblance  to  pneumococcus. 
503  ;  resistance,  517  ;  in  rheumatic  fever,  520  359  ; 
in  scarlet  fever,  26,  520,  521,  533 ;  serotherapy, 
534-536 ;  serums,  univalent  and  polyvalent,  533 ; 
streptocolysin.  519,  520 ;  symbiosis  with  B.  inffu- 
enzWj  564 ;  tissue  reactions,  144 ;  toxic  properties, 
519,  520,  529  ;  toxin  for  erythrocytes ;  see  Strepto- 
colysin ;   toxin  for   leucocytes,   519  ;   in  tuberculosis, 

521,  522,  591,  592 ;  tumors,  influence  on.  529  ;  in 
typhoid  fever,  439  ;  unity,  question  of.  532  ;  varie- 
ties,  516  ;   virulence,   518. 

Streptococcus    scarlatinw    527 

Streptocolysin     .  . '. 519,  520 

Streptothrix,    infections    with 634 

Streptothrix    madurcc    634 


782  INDEX. 

PAGE 

Substance    sensihiUsatrice     262,  861 

Summer  diarrheas  ;  see  Dysentery,  acute  epidemic. 

Surra  ;  see  Trypanosomiasis  in  animals 681 

Susceptibility     130,   158,   159 

See  the  individual  diseases. 
Symptomatic  anthrax. 

Antitoxin,  203  ;  vaccination  against,  363. 

Syncytiolysin     301 

Synonyms    361 

Syntoxoids    196,  353 

Syphilis     25,  646,  652 

Animals,  non-susceptibility  of,  646 ;  bacillus  of  De 
Lisle  and  Julien,  646 ;  bacillus  of  Joseph  and 
Piorkowski,  646  ;  bacillus  of  Lustgarten,  646  ;  Colle's 
law,  651 ;  immunity  and  susceptibility,  158,  651  ; 
inheritance,  651  ;  micro-organisms  found  ini  646 ; 
monkeys,  transmission  to,  648  ;  other  animals,  trans- 
mission to,  649  ;  Profeta's  law  in.  651 ;  reinfection, 
650,  651  ;  Spirocheta  pallida  in.  644  ;  transmission, 
650 ;  virulence,  variations  in.  650 ;  virus,  distribu- 
tion of,  650 ;  virus,  non-filterability  of,  650 ;  Was- 
sermann  test  in,  284. 

Tetanolysin     413,  414 

Antitetanolysin,  367  ;  neutralization  by  cholestrin,  204. 

Tetanospasmin      413,  414 

Tetanus    25,  408-419 

Agglutination  reaction,  419  ;  animals,  susceptibility  of, 
156;  cerebral,  415;  dirt  and  necrotic  tissue,  influence 
of,  411 ;  dolorosa,  415 ;  excretion  of  toxin,  414  ; 
Fourth  of  July,  412,  416 ;  "head  tetanus,"  414  ; 
in  horses,  416 ;  immunity  and  susceptibility,  129, 
169,  315.  413,  415  ;  "idiopathic,"  412 ;  incubation 
period.  412  ;  leucocytes,  in  absorption  of  toxin,  413  ; 
local,  415  ;  mixed  infections,  31,  411,  412  ;  nervous 
tissue,  in  fixation  and  transport  of  toxin,  414 ; 
occurrence  of  bacillus  in  the  body,  412 ;  occur- 
rence of  toxin  in  the  body,  413 ;  pathogenesis, 
413,  414 ;  phagocytosis  in,  315,  411 ;  puerperal, 
416  ;  rheumaticus,  412  ;  seasons  in  relation  to  prev- 
alence. 412  ;  serotherapy  and  prophylaxis,  368,  416, 
418;  toxin  (see  B.  tetani,  toxin  of)  ;  treatment  of 
wounds,  416 ;  Wassermann's  experiment,  414  ; 
wounds  favoring  development  of,  410  ;  see  Bacillus 
tetani. 

Texas  fever    684-686 

Thrush     639 

Organisms  of,  639 ;  susceptibility  to,  640 ;  systemic 
infections,   640. 

Thyrotoxin     303 

"Tick   fever ;"    see    "Spotted   fever." 

Timothy    bacillus     614 

Toxins. 

Absorption  of,  106;  animal,  21,  428-431;  attenuation 
of,  181  ;  bacterial,  21,  378  ;  see  individual  bacteria 
chemotaxis,  influence  on,  315,  520,  539  ;  crotin,  427 
degenerative  changes  in,  193,  353  ;  endotoxins,  179  , 
see  individual  bacteria ;  gastric  juice,  destructive 
action,  141  ;  haptophores  of.  192,  353  ;  see  side-chain 
theory ;  immunization  with.  181,  364 ;  incubation 
period  of,  176.  415;  intracellular;  see  Endotoxins; 
leucocidin,  539 ;  leucocytes  in  absorption  of,  147, 
321  ;  modifications  by  age,  198  ;  neutralization  by 
antitoxins,    391,    344;    pancreatic   juice,    destructive 


INDEX.  783 

PAGE 

action,  142  ;  phallin.  428  ;  of  pollens,  420  ;  precipi- 
tation of,  177  ;  preparation,  177  ;  properties  of,  170, 
ii52  ;  as  receptors  of,  second  order,  .'iOl  ;  ricin,  427  ; 
robin,  427  ;  secondary  or  adventitious,  178 ;  toxin 
Spectrum,  194,  353  ;  standardization  of,  183  ;  staph- 
ylolysin,  538  ;  structure,  191  ;  toxophores,  193,  353  ; 
see  side-cliain  theory  ;  union  with  tissue  cells,  177, 
200,  344,  348,  300,  308.  415 ;  vegetable,  21,  425- 
428 ;    see    individual    micro-organisms. 

Toxoids     193-190,   353 

Toxon 195,  35,  400 

Toxophorous   group,    toxophore    193,  351 

Trichomonas  intestinalia,  morphology  and   pathogenicity 

of    093,  694 

Trichomonas   vaginalis    693 

Trichophyton     640 

Tritotoxin      196,  353 

Trypanosoma     670 

Agglutination  of,  071  ;  cultivation  of,  679,  681  ;  mor- 
phology of,  670 ;  multiplication  of,  671  ;  rosette 
formation  by,  071  ;  sleeping  sickness,  673 ;  species 
of,    670,    671,    677 ;    trypanosomatic    fever,   673. 

Trypanosomatic    fever     673 

Sleeping  sickness,  relation  to,  673,  674  ;  symptoms 
of,    674  ;   trypanosomes   in,   674. 

Trypanosomiasis    670-684 

Agglutination  reactions,  684  ;  immunity  and  suscepti- 
bility, 683  ;  in  man,  673-677  ;  parasites,  occurrence 
of  in  the  blood,  678  ;  serotherapy  of,  684  ;  "trypan- 
roth"  in  treatment  of,  684 ;  vaccination  in,  683 ; 
see  Sleeping  sickness  and  Trypanosomatic  fever. 

Trypanosomiasis    in    animals 678-683 

Dourine,   682  ;  horses,  cattle  and  mules.  680-683  ;  mat 
de  cederas,  682  ;  nagana,   680  ;  in  rats,  679  ;  surra, 
681  ;    symptomatology,    678. 
"Trypanroth"    in   treatment   of   trypanosomiasis.  ..  .683,  684 
Tsetse    flies,    in    transmission    of    trypanosomiasis ;    see 
Trypanosomiasis. 

Tuberculin  of  Koch  and  others 363,  364,  578,  579,  580 

Dangers,  errors  and  limitations  in  use,  601,  602; 
diagnostic  use  of,  599-603.  612  ;  disturbances  caused 
by,  599  ;  immunization  with,  577,  598.  599  ;  prepa- 
ration of.  578  ;  principles  of  action,  606  ;  specificity 
of.  001.  002  ;  standardization  of,  578,  580  ;  therapy, 
002.   003. 

Tubf-rculocidin     580 

Tuberculosis     25,   573-615 

Agglutination  as  an  indox  of  immunity  to,  607 ;  ag- 
glutination reaction,  607,  610  ;  amyloid  degeneration 
in,  591  ;  "anatomic  tubercle,"  585  ;  in  animals,  593, 
611  ;  avian.  012;  bovine.  Oil  ;  bovine,  relation  of,  to 
human,  582,  583  ;  congenital,  584  ;  disinfection  in, 
593;  dissemination  by  means  of  phagocytes.  588; 
"droplet  infection,"  585 ;  "dust  infection,'  585 ; 
healing,  spontaneous,  587  ;  heredity  in,  596  ;  immu- 
nity and  susceptibility.  128,  130,  169,  593,  597,  599, 
607  ;  immunization,  mixed.  609  ;  infection  atria,  585. 
580;  infectiveness  of,  573;  latent,  584;  lupus  vul- 
garis, 585;  metastases  in.  580;  miliary.  587;  mixed 
infections  in.  501;  organs  attacked,  585,  580;  pha- 
gocytosis, 588  ;  pneumonia  during.  510 ;  predispos- 
ing factors  to.  595 ;  primar.v  and  secondary,  587 ; 
prophylaxis,     592,     593 ;     pulmonary,     585 ;     sero- 


784  INDEX. 

PAGE 

therapy,  592,  608  ;  streptococcus  in,  520,  522 ;  tis- 
sue changes  in,  20,  588,  591  ;  tuberculin  in 
diagnosis.  599,  607 ;  ulcerative,  585 ;  vaccination 
against,  609. 

Tumors,  influence   of  streptococcus  on 529 

Turtle   poison,   antitoxin   for 203 

Typhoid    fever    25,  433-449 

Agglutination  reaction,  23.  209,  448,  449  ;  antibodies, 
origin  of,  320  ;  bacillemia,  437  ;  bacilli,  distribution 


uty 
ceptibility,  161,  167.  169.  439 ;  infection  atrium, 
437 ;  leucocytes,  439,  442 ;  leucotoxin  in  experi- 
mental infections,  298 ;  mixed  immunization,  378 ; 
mixed  infections  in,  439 ;  prophylaxis.  442 ;  serum 
properties,  132 ;  serum  prophylaxis,  443  ;  serother- 
apy, 374,  447 ;  therapy,  active  immunization,  448 ; 
therapy  of  Jez.  447  ;  vaccines  and  vaccination,  166, 
362,  443,  446  ;  see  B.  typhosus. 

Typhus    fever    25,   725-728 

Conditions  for  development,  726  ;  contagiousness,  726  ; 
endemics  of,  725  ;  immunity  in,  727 ;  micro-organ- 
isms in.  727  ;  occurrence,  725  ;  transmission  to  ani- 
mals,   727 ;    transmission   by   lice,    727. 

Ultramicroscopic    micro-organisms    27 

Undulant  fever  ;  see  Malta  fever. 

Univalent    serums    533 

Urease    •  •  •  •    ^^^ 

V^accination    5,    165,'  362-364,"  3V6-380 

Antibodies  produced  by.  377 ;  duration  of  resistance 
caused  by.  376  ;  incubation  period,  relation  to,  378  ; 
see  Smallpox  and  Hydrophobia ;  "positive"  and 
"negative  phases,"  377 ;  substances  used  for,  362- 
364  ;  see  the  individual   diseases. 

Vaccines    362-364,  376-380 

See  the  individual  diseases. 

Vaccinia  ;   see  Smallpox  and  Vaccinia. 

Varicella  ;   see   Chickenpox. 

Variola  inoculata   734 

Variola  ;  see  Smallpox. 

V'enoms    1,   177,   191.  198,   273-275,  428-431 

Amboceptors  and  complements,  273,  274,  430 ;  anti- 
veuins,  174,  430,  431  ;  character  of,  from  different 
snakes.  429  ;  cobralecithid.  275.  429  ;  cvtotoxins  of, 
429 ;  endocomplements  for.  274.  430 :  endothelio- 
toxin  of.  428  ;  ferments  of,  429  ;  hemagglutinins  of, 
428 ;  hemolysin  of,  273,  428 ;  hemorrhagin,  273, 
428  ;  incubation  period,  177.  431  ;  lecithin  as  com- 
plement, 274,  430  ;  neurotoxin  of.  273,  428  ;  radium, 
effect  of.  431  ;  structure  of  cytotoxins  of,  429  ;  tox- 
ins of.   273 ;   toxoids  of,  428. 

R6r?o  (holerw. 
Acquired  immunity  to.  316  ;  action  of  gastric  juice  on, 
141  ;  active  immunity,  formation  of  specific  precipi- 
tin in,  479  ;  agglutination  of,  bv  normal  serum,  206  ; 
agglutination  of,  480  ;  agglutinins.  206  ;  attenuation 
of,  161  ;  autolytic  products,  vaccination  with,  478  ; 
discovery,  469  ;  endotoxin  of.  475  ;  identification  of, 
by  ag'glutination  reaction  and  by  Pfeiffer  experi- 
ment. 471  ;  in  Pfeiffer's  phenomenon,  247  ;  in  stools 
of  convalescents,  472;  location  in  infeoted  body, 
475 ;    morphology,    staining    properties   and    cultiva- 


l^DEX.  785 

tion  of,  470,  471  ;  non-neutralization  of  endotoxin  of, 
by  its  specific  bactericidal  serum.  253 ;  occurrence 
of  water,  472  ;  resistance  and  viability  of,  471  ;  see 
Cholera;  symbiosis  with  Ameba  coli,  088;  soluble 
toxin,  475  ;  specificity  of,  24  ;  toxicity  of  culture 
filtrates,  475  ;  toxicity  of  killed  cultures,  475. 

Vibrio     metchnikovi     Iq 

Virulence 88 

Increase  of,  in  the  presence  of  other  micro-organisms, 
31  ;  influence  of.  on  inflammatory  reaction  144  ; 
relation  of,  to  phagocytosis,  315  ;  specialization  of, 
89 ;   see   different  micro-organisms. 

Virulin     121    338 

Wasp   Poison,    antitoxin    for '  '>oji 

Wassermann    reaction     '  '  "  '    2?54 

Antigen  in,  285  ;  technic.  286  ;  value  of,  290  ;  in'  non- 
syphilitic  diseases,  291. 

Whooping   cough    (pertussis)     7.50-755 

Contagiousness,  753,  754  ;  cultural  characteristics  and 
pathogenicity  of  the  influenza-like  bacilli,  751  : 
immunity  and  susceptibility,  754  ;  influenza-like 
bacillus  in,  751  ;  influenza-like  bacillus,  relation  to 
whooping  cough,  753  ;  Micrococcus  catarrhalis  in, 
ooO  ;  micro-organisms  in,  750  ;  prophylaxis,  7.54  ; 
pseudoinfluenza  bacilli  in.  565 ;  serotherapy,  754  • 
virus,  dissemination  of,  753. 
"Water-borne"    epidemics;    cholera,    dysentery,    typhoid. 

435,   457    473 

Welch,    hypothesis   of    '  33.> 

Widal    reaction    '.■.'.■.■.'.■.■.■.■.■.206,  22.5 

bee   Agglutination. 
Wool-sorters"   disease ;   see   Anthrax. 
Wright's  method  of  vaccmation. 

Staphylococcus    infections,    548 ;    tvphoid    fever     443 
444.  '  '  ' 

Yellow    fever    25    711-7'>0 

Acclimatization,  question  of.  719 ;  altitude  and  mois- 
ture, relation  to.  715  ;  Bacillus  icterrndes  in,  712. 
713;  cold,  relation  to,  715;  epidemiologv,  715; 
fomites,  714,  715 ;  immunity,  acquired,  714,  720 ; 
importation  by  ships.  718  ;  incubation  period,  714  ; 
mosquito  theory  of,  712;  se  also  Ster/omyia  fasciata; 
non-contagiousness  of.  715 ;  occurrence,  711  ;  pro- 
phylaxis and  quarantine  of,  715.  716,  718,  719 ; 
virus,  filterability  of,  714 ;  virus,  resistance  of, 
,_    <  18  ;   serotherapy,   720;   susceptibility  to,   719. 

Zooprecipitins    23.'> 

Zootoxins    .....'..'.'.....'.... 43*] 

Zwischenkorper,    synonyms    for!  ...[.............  '>QS 

Zymotoxic   groups    .'.■.■..'.'.'.■,■.  222 


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